Glossary of Automotive Terms – D

Letter D – Dictionary of Automotive Terms

  1. Abbreviation for diesel.
  2. Abbreviation for drive.
  3. A mark on the output (live) terminal on a generator (contrasts with F)
A bicycle maneuver in which the rider puts a foot down in order to catch his balance on a difficult section of trail as in, ‘You will be disqualified if you dab on this course.’
  1. Abbreviation for Digital Audio Broadcast.
  2. Abbreviation for Delayed Accessory Bus


A South Korean automobile manufacturer which produced Lanos (1999-2002), Nubira (1999-2002), Leganza (1999-2002).

Abbreviation for Delivered at Frontier and coupled with a named place. The seller fulfills his obligation to deliver when the goods have been made available, cleared for export, at the named point and place at the frontier but before the customs border of the adjoining country. The term ‘frontier’ may be used for any frontier including that of the country of export. Therefore it is of vital importance that the frontier in question be defined precisely by always naming the point and place in the term.
Dagmar (Virginia Ruth Egnor)Virginia Ruth Egnor

1955 Cadillac1955 Cadillac ‘Dagmar’ bumper

  1. Large bullet-shaped protrusion on bumpers of cars in the 1950s. It was named after the nickname of a buxom television star, Virginia Ruth Egnor (1921-2001).
  2. Dagmar is an automobile of which only the 6-80 models are classic cars.


A brand of automobile from the Daihatsu Motor Co., Ltd. which began in 1951 and included the following models Rocky (1987-98), Charade (1977-2000)

Also called Austro-Daimler. A vehicle brand of which the several models with required application are classic cars such as

  1. All 8 and 12 cylinder from 1925-48
  2. 1925-34 6 cylinder, 3 1/2 litre and larger models
  3. 1925-34 models 25, 25/85, 20/25, 20/30
  4. 1925 model 30
  5. 1925-32 models 30, 35/120
  6. 1925-26 model 45

The 1949-53 DE-36 Custom Built models are milestone cars. The 1949-53 2.5 Special Sport Convertible models are Milestone cars.

Dalton’s law
Vapor pressure created in a container by a mixture of gases is equal to sum of individual vapor pressures of the gases contained in mixture.
  1. To reduce the oscillations of spring, carburetor piston, etc.
  2. To reduce the vibration in a crankshaft
Dampening belt
A rubber belt wound around the outside of a brake drum or rotor prior to machining the drum or rotor. The belt dampens out vibrations that might affect the quality of the finished surface.


  1. A friction device sometimes called a shock absorber. Used for controlling and damping spring oscillations. The springs actually absorb road shocks; the dampers convert the energy imparted to the springs into thermal energy (heat) (by friction), which is dissipated to the atmosphere or the vehicle’s chassis. Dampers are distinguishable by the type of friction involved, mechanical or hydraulic but most modern cars used tubular-shaped hydraulic shock absorbers. Because they affect up and down wheel motions, dampers are an important link in tuning a vehicle’s ride and handling.
  2. Device which uses oil metered through orifices to control abrupt suspension movement.
  3. A movable plate which permits or restricts the flow of liquids or gasses.
Damper piston
A piston in a cylinder whose movement is restricted by a liquid or gas, which thus also restricts the movement of another member to which it is connected.
Damper rod
On a motorcycle, a tube secured to the bottom of each fork slider to hold the slider on the fork leg. Controls front suspension movement by metering hydraulic fluid through orifices in the rod.
Damper settings
Damper springs
Springs in a clutch plate providing a cushion against sudden loads due to abrupt engagement
Damper strut
A suspension strut whose hub carrier is attached to the spring element rather than to the damper tube. Compare Macpherson strut
  1. Cushioning of force.
  2. The action of suspension to control the speed of movement through its travel, usually by a piston running through oil and thus gives a smoother ride. It vastly improves that smoothness of ride offered.
Damping force
The amount of cushioning applied by a shock absorber
Damping rate
The amount of cushioning applied by a shock absorber
Damping restriction
The bore of a small cross section in the fuel distributor of the K-Jetronic type system. It dampens sensor plate movement in the air flow sensor during high load and low rpm conditions
A car manufacturer of which the 1920-1926 8 cylinder Model D are classic cars
Dark 30
Trucker slang for nighttime as in ‘I am shutting this rig down right at dark 30.’
Trucker slang for nighttime as in ‘I am shutting this rig down right at darktime.’
A vehicle manufacturer in which only the 8-cyl. cars and 4-litre, 6-cyl. cars of 1925-1948 are classic cars.


Dash board


In very early cars, an upright wooden or metal panel at the front of the body. This was a holdover from days when the dashboard literally shielded the carriage from the horse manure and road splash that would dash up to the riders. In more modern cars, the word ‘dashboard’ is sometimes used interchangeably with the more correct term, instrument panel which contains the driving instruments, switches, etc. Sometimes called dash panel or just dash.
Dashboard gearchange
British term for Dash shifter
Dashboard plaque
  1. A metal or plastic plate which is mounted to the instrument panel to indicate the brand, model, or series of vehicle.
  2. A metal plate which is mounted to the instrument panel to indicate an award for attending or winning a rally or other automotive event.
Dash design
Dash line
A term used in body engineering. In some car companies, the ‘dash line’ is an all-important measuring marker from which body-length dimensions are taken. During design, the actual ‘dash’ (firewall) is extensively altered to accommodate intrusion by the transmission, ducting, controls, etc., so it rarely coincides with the theoretical ‘dash’ and should never by confused with instrument panel
Dash panel
  1. A structural panel with bracing across the width of the car on the inside of the bulkhead below the windshield that provides the mounting locations of the dashboard. Also called the fire wall because it is the partition between the passenger compartment and the engine compartment.
  2. The Bulkhead
Dash plaque
  1. A metal or plastic plate which is mounted to the instrument panel to indicate the brand, model, or series of vehicle.
  2. A metal plate which is mounted to the instrument panel to indicate an award for attending or winning a rally or other automotive event.
A unit using a cylinder and piston or a cylinder and diaphragm with a small vent hole, to retard or slow down the movement of some part.

(DP) a diaphragm that controls the rate at which the throttle closes
Dash shifter
A shift lever and indicator which is located on the instrument panel either as a short lever or push buttons
The distance from the dash line or point to the front-axle centerline in side view. This is a crucial dimension in creating interchangeable body programs.
Data Center
Data Interchange
Data link connector
Connector(s) providing access and/or control of the vehicle information, operating conditions, and diagnostic information.
Data Sheet
Data System
Date Code
A label that shows when a product was manufactured.

Datsun booksClick image for books on

A model of automobile manufactured by Nissan

Datsun Truck
Datsun Truck BooksClick image for books on
Datsun Truck

A model of truck manufactured by Nissan

Datsun Z
Datsun Z BooksClick image for books on
Datsun Z

A model of automobile manufactured by Nissan

Datum line
See Horizontal Zero Line
A crane arm for handling lifeboats, stores, etc.
Day Cab
A truck or tractor without a sleeper birth. Typically used for day trips or local routes.
Daylighting controls
A system of sensors that assesses the amount of daylight and controls lighting or shading devices to maintain a specified lighting level. The sensors are sometimes referred to as photocells.
Daylight opening
(DLO) The perimeter of any car window, including the windshield and backlight.
Day-night mirror
A mirror which adjusts to prevent the glare from the headlights of following cars. The British term is dipping mirror.
Days’ supply
Number of days needed to sell all vehicles in inventory, based on the previous month’s sales rate.
Daytime running lights
(DRLs) A safety-oriented lighting system in which the headlights or other front lights are constantly on even during the day. They help to prevent possible accidents because oncoming traffic can be seen. December 1, 1989, Canada became the second country after Norway to require daytime running lights on all new passenger vehicles. In other countries the implementation of DRLs has had mixed response.
The glare from the headlights of oncoming traffic which can momentarily blind a driver.
Dazzle mirror
Abbreviation for Decibels
  1. A unit of measure for decibels, the measure of sound intensity or pressure named after Alexander Graham Bell. It is a logarithmic measurement; every 3dB increase represents a doubling of the sound pressure. The A in dBA indicates that the measurement was taken with an A-weighted scale; sound pressure varies across the audible spectrum, and the A-weighted scale approximates the human ear’s sensitivity to various frequencies.
  2. DBA is an abbreviation for Doing Business As a common usage for a business license.
Abbreviation for De Danske Bilimport rer’ (Denmark)
Abbreviation for double, as in dbl.-wide rear wheels.
  1. As an electrical term, it is an abbreviation for Direct current.
  2. As a piston position, DC is an abbreviation for Dead center where the piston at the extreme top or bottom of its stroke.
  3. Abbreviation for Duty Cycle
  4. Abbreviation for Distribution Center. A warehouse that manages and distributes inventory per the direction of corporate systems and customer demand.
DC generator
On a motorcycle, a crankshaft-driven electrical generator that uses spinning coils to produce direct current.


Abbreviation for DC Motor Idle Speed Actuator
Abbreviation for Data Communication Link
DC rim
Abbreviation for Drop-Center rim
DD Form 836
A special ‘instructions for motor vehicle drivers’ form issued by a government agency when transporting hazardous materials for the U.S. government. The pickup driver and the delivery driver must read and sign the form; the delivery driver gives it to the consignee when delivering the shipment.
Abbreviation for Distillers Dried Grains — An animal feed coproduct consisting of residual grain solids that have been dried to a moisture content of 10-12%.
Abbreviation for Distillers Dried Grains with Solubles — An animal feed coproduct very similar to DDG but also containing the process syrup as well as residual grain solids.
Abbreviation for Diagnostic Data Link
Abbreviation for Delivered Duty Paid plus the named place of destination. The seller fulfills his obligation to deliver when the goods have been made available at the named place in the country of importation. The seller has to bear the risks and costs, including duties, taxes, and other charges of delivering the goods thereto, cleared for importation. While the EXW term represents the minimum obligation for the seller, DDP represents the maximum obligation.
Abbreviation for Delivered Duty Unpaid plus the named place of destination. The seller fulfills his obligation to deliver when the goods have been made available at the named place in the country of importation. The seller has to bear the costs and risks involved in bringing the goods thereto (excluding duties, taxes, and other official charges payable upon importation as well as the costs and risks of carrying out customs formalities). The buyer has to pay any additional costs and to bear any risks caused by his failure to clear the goods for import in time.
Abbreviation for Drive End
Dead axle

Dead AxleDead Axle

An axle that does not rotate nor is driven but merely forms a base upon which to attach the wheels. Non-powered rear axle on tandem truck or tractor. Also called tag axle

Dead band
The change in speed required before the governor will make a corrective movement of the throttle. This hesitation results from the lag in governor action caused by friction and lost motion in the governor mechanism. Also called sensitivity.
Dead battery
A battery that registers almost no electrical charge. Sometimes it can be brought back to life with a charger. The British call it a flat battery
Dead center
The point at which the piston reaches its uppermost or lowermost position in the cylinder the rod CrankJournal would be at 11 o’clock UDC or 6 o’clock LDC.

Dead end
A road which has no outlet
Dead Flat
  1. A portion of a ship’s side or bottom where the plating has no curvature; also, the midship portion of constant cross section — the parallel middle body.
  2. A section of road that is absolutely flat. A term often used for a road that is relatively flat since few roads are without at least some minor undulations.
Dead freight factor
The amount of a ship’s carrying capacity that is not used.
Dead Head
  1. A cargo truck or trailer without any cargo that is being driven to a particular location
  2. A trip where the tractor pulls an empty trailer or a trailer loaded with cargo that generates no revenue. Sometimes it can be company materials or goods
  3. A ride-along driver
Operating a truck without cargo.
Dead-head pressure
A fuel pressure reading taken directly at the fuel pump outlet. Many systems use a fuel pressure regulator; dead-head pressure is an unregulated measurement
Dead Man
A buried timber (etc.) that has an attached pipe or cable going to the surface for the purpose of securing a vessel at a dock or along a riverbank.
Dead pedal
A footrest located to the far left of the driver so that he can brace his left leg during hard cornering or to balance the position of the right foot on the throttle pedal during normal driving.
Dead rear axle
A rear axle that does not turn. E.g., rear axle of front wheel drive car
Dead rise
The upward slant or rise of the bottom of a shiip from the keel to the bilge
Dead space
The space below the piston available for pre-compression of the incoming fresh charge of the two-stroke engine.
Dead Stock
Product that has been in inventory for an extended period of time without being moved or ordered.
The total weight in tons (2240 lb.) that a ship carries on a specified draft including fuel, water in tanks, cargo, stores, passengers, baggage, crew and their effects, but excluding the water in the boilers. It is the difference in weight between a vessel when it is fully loaded and when it is empty measured by the water it displaces.
Deadweight tons
(DWT) The lifting capacity of a ship expressed in long tons, including cargo, commodities, and crew.
  1. A firm that buys and sells, adding some value for the consumer in the process. Dealer often means a firm which operates closer in the distribution channel to the consumer than a distributor or wholesaler and may add more value for consumers than either of the above-mentioned terms. Also called dealership.
  2. A person whose business is buying and selling cars and trucks or motorcycles.
Dealer invoice
The price the dealer pays for a vehicle.
Dealer participation
The amount contributed by the dealer to reduce the final purchase price in the lease contract. Dealer participation can take the form of a rebate or simply a discount. The dealer participation is reflected in the lease contract as a capitalized cost reduction.
Dealer principal
The individual or corporation that owns and controls one or a number of auto dealerships.
  1. A firm that buys and sells, adding some value for the consumer in the process. A dealership often means a firm which operates closer in the distribution channel to the consumer than a distributor or wholesaler and may add more value for consumers than either of the above-mentioned terms.
  2. A local franchise individually owned, but supported by a vehicle manufacturer, that sells and services the manufacturer’s vehicles.
Dealer tank wagon sales
(DTW) Wholesale sales of gasoline priced on a delivered basis to a retail outlet.
Act of separating air from substances.
Death rattle
An informal term for a noise from an engine which indicates that it is likely to break down at any moment
The process of locating and correcting faults in a system
To remove Burrs from a metal surface
Removing chips, rough edges, burrs, and other imperfections from a metal surface, object, or bearing usually by grinding.
Abbreviation for Digital Electronic Controller
A sticker or transfer which is applied to a smooth surface to identify a particular product or provide a fancy design. Pronounced dee-KALL in the United States, but DECK-ull in Canada.
The action of removing carbon buildup from the surface of the cylinder head and the dome of the piston. The accumulation of carbon indicates poor combustion and will result in loss of performance.


Ten therms or 1,000,000 Btu.
A term for hydraulic pressure reduction that occurs during an ABS stop

The action of slowing down. The opposite of accelerate.
Negative acceleration; the rate of change in velocity as a vehicle slows down during braking.
Deceleration device
Deceleration fuel cut-off
A device which stops the flow of fuel to the carburetor or injectors when the vehicle rapidly decelerates in the event of a crash thus preventing the possibility of a fire or explosion.
Deceleration switch
A device that signals the rate of vehicle deceleration to the ECU, allowing it to adjust ABS operation accordingly
An instrument for measuring deceleration.
(dB) Unit used for measuring relative loudness of sounds. One decibel is equal to approximate difference of loudness ordinarily detectable by human ear, the range of which is about 130 decibels on scale beginning with one for faintest audible sound.
  1. The bed of a half-ton truck.
  2. The floor of a commercial vehicle like a bus.
  3. The trunk lid of a car. Also called rear deck.
  4. The upper surface of the luggage compartment.
  5. In an engine, top face of the cylinder block on which the cylinder head mounts.
  6. Insulated horizontal partition between refrigerated space and evaporator space. Also called coil deck
  7. A platform in a ship corresponding to a floor in a building.
  8. One or more boards or panels comprising the top or bottom surface of a pallet.
  9. The process of removing the body trim or contour lines from the hood or trunk of a car, usually as part of a customized design.
Deck beam
An athwartship horizontal structural member supporting a flat or deck
Deck Board
The element or component of a pallet deck, oriented perpendicular to the stringer or stringer board. Also see:

Deck Board Spacing
The distance between adjacent duckboards.
Deck Board Span
The distance between deck boards that supports stringers, stringer boards or blocks.
The condition after removing the body trim or contour lines from the hood or trunk of a car, usually as part of a customized design.
Deck height
The center of the crankshaft main-bearing bores to the block deck surface.
Deck house
Small superstructure (shelter) on the top deck which contains the steering wheel and other navigational instruments.


Deck landing
Deck lid
  1. The panel which covers the engine in a vehicle with the engine in the rear of the car.
  2. The lid of the luggage compartment.


Deck Mat
The assembly of deck boards and stringer boards, which form the deck of block pallets.
Deck Pallet
Deck panel
The sheet metal panel extending from the bottom of the rear window to the rear panel and enclosing the cutout for the trunk lid, extending sideways to the top of both rear fenders. In some cases, this panel covers only the area between the bottom of the rear window and the front edge of the trunk lid.

Deck Set
Colloquial term for piggyback hauled trucks.


Deck ship
Deck stringer
The strake of deck plating that runs along the outboard edge of a deck
Declared value
  1. Assumed value of shipment unless shipper declares higher value.
  2. Stating lower value on a shipment to get a lower rate.
Inclination of shipways to provide for launching.
The action of disengaging the clutch (i.e. releasing the clutch pedal or lever).

To Decarbon
A valve which is manually operated to release compression in a cylinder by allowing air to escape in order to facilitate manual starting of an old engine or a diesel engine. Some motorcycles also used a decompressor to assist in kick-starting.
Decreasing-radius corner
A turn where the arc gets sharper as you progress through the curve
Something that is designed for a specific use or for a specific vehicle.
Dedicated reserves
The volume of recoverable, salable gas reserves committed to, controlled by, or possessed by the reporting pipeline company and used for acts and services for which both the seller and the company have received certificate authorization from the Federal Energy Regulatory Commission (FERC). Reserves include both company-owned reserves (including owned gas in underground storage), reserves under contract from independent producers, and short-term and emergency supplies from the intrastate market. Gas volumes under contract from other interstate pipelines are not included as reserves, but may constitute part or all of a company’s gas supply.
Dedicated Vehicle
A vehicle designed to operate solely on one alternative fuel, as opposed to a converted vehicle which was later altered to use an alternative fuel. Generally, dedicated vehicles provide superior emissions and performance results because their design has been optimized for operation on only one fuel. A vehicle powered by an electric motor is not to be treated as dedicated.
De Dion axle

De Dion AxleDe Dion Axle

A rear axle setup developed by Count de Dion in the 19th century in which the driving wheels are attached to curved dead axle that is attached to the frame by a central pivot, the differential unit is bolted to the frame and is connected to the driving wheels by drive axles using Universal joints. The De Dion system keeps the wheels upright (the same as a Live axle does), but Unsprung weight is reduced because the differential is out of the axle. De Dion suspension also leaves room around the differential for inboard brakes, which can further reduce Unsprung weight.

Deep cycling
The process of discharging a battery almost completely before recharging
Deep Drawing
Forming shaped articles or shells by forcing sheet metal into a die.
Deep-Lane Storage
Product that is stored more than one unit deep in an aisle.
Deep Link Conveyor Chain
Chain design with a carrier roller which protrudes down below the side bar but does not protrude above the side bar.
Deep tank
Tanks extending from the bottom or inner bottom up to or higher than the lowest deck of a ship
Deer alert

Deer AlertDeer Alert

A device which is mounted on the outside of a vehicle and which makes a high-pitched sound to warn deer and other animals away. Whether it really works or not is debatable.

  1. A fault in a system or a flaw in materials or a finish
  2. A faulty condition of a vehicle with a broken mirror, missing lighting, inoperable component, etc.
A description of a component which is faulty or flawed.
Defense District
Defense Fuel Supply Center
(DFSC) Used by all branches of the Department of Defense (DOD)
Defensive driving
A driving technique in which the driver prepares for and watches for the mistakes of other drivers around him so that he can avoid an accident.
Deferred Rebate
Carrier returns a portion of freight charges to shipper. In exchange, shipper gives all/most shipments to carrier over specified period, usually six months. Rebate payment is deferred for similar period.
Abbreviation for Digital Electronic Fuel Injection (Cadillac)
An air chamber (like a tire or lumbar support chamber) which has lost all its air.
The loss of air from a tire or other air chamber
Deflation warning system
(DWS) developed by Dunlop for on-line detection of tire pressure loss. When tire pressure is reduced, the tire circumference is also reduced resulting in increased wheel rpm. The system uses the wheel speed sensors of an existing ABS system to continuously monitor wheel speed and tire condition, and triggers a warning signal upon detecting a problem.
  1. The movement of a suspension piece when subjected to a load.
  2. The amount of deformation or bending in a pallet or pallet component under load.
Deflection rate
The distance that a spring squeezes together (deflects) in relation to the pressure applied. E.g., 5 inches per 1000 lb load.
Deflection under load
A truck mounted machine which produces a continuous record of highway strength by measuring its deflection under load.
  1. A device which causes bugs, tar, and grime from hitting other components.
  2. A special piston profile used to achieve cross scavenging in earlier two-stroke engines.
Deflector piston
A piston design which had a crown designed to direct the incoming fresh mixture upwards to expel the burnt exhaust gas from the cylinder. This design is no longer used today.
Deflector shield
The action of removing mist or condensation from the inside of a window or the outside of a mirror by means of blowing air or heated wires imbedded in the glass. The British term is demist.


An electric or hot air device to remove the fog or ice from both the inside and outside of the windshield, Backlight (i.e., rear window) or even mirrors. Some are designed to remove fog from the side windows.
Defogging system
An alteration of shape or dimension which is caused by stress, expansion, or contraction because of temperature, humidity, or metallurgical changes.

Deformation zone
A Crumple zone
The action of removing frost from the inside of a window or the outside of a mirror by means of blowing air or heated wires imbedded in the glass.

Defrost Control
Defrost cycle
Refrigerating cycle in which evaporator frost and ice accumulation is melted.
The apparatus (either a fan connected to the heating system or electrical wires imbedded in the glass) which removes frost or fog from a window. Also called a demister.
Process of removing frost accumulation from evaporators.

Defrosting control
Device to automatically defrost evaporator. It may operate by means of a clock, door cycling mechanism, or during off portion of refrigerating cycle.
Defrosting type evaporator
Evaporator operating at such temperatures that ice and frost on surface melts off during part of operating cycle.
Defrost timer
Device, connected into electrical circuit, which shuts unit off long enough to permit ice and frost accumulation on evaporator to melt.
Degasification system
The methods employed for removing methane from a coal seam that could not otherwise be removed by standard ventilation fans and thus would pose a substantial hazard to coal miners. These systems may be used prior to mining or during mining activities.
The action of removing the smooth Finish on cylinder walls so that a new set of rings will seat.
An abrasive tool used to remove the glaze from cylinder walls so that a new set of rings will seat.

Process used to remove the glaze from cylinder walls before new piston rings are installed.
Degradable organic carbon
The portion of organic carbon present in such solid waste as paper, food waste, and yard waste that is susceptible to biochemical decomposition.
The deterioration in the condition of something.

Degradation Rate
  1. To remove oil and grease from the surface of a part.
  2. Wiping the surface to be painted with a clean cloth saturated in a Solvent. This is essential to good paint Adhesion.
A substance which removes dirt and Grease from a mechanic’s hands. Also called hand cleaner.
  1. The removing of grease or oil from a surface.
  2. Solution or solvent used to remove oil or grease from refrigerator parts.
Degreasing agent
A solvent or alkaline solution which is used for removing oil and grease
1/360 part of a circle.
Unit that represents one degree of difference from inside temperature and the average outdoor temperature for one day; often used in estimating fuel requirements for a building.
Degree wheel

degree wheelDegree Wheel

A wheel-like disc divided into 360 equal parts that is temporarily attached to the engine crankshaft to time the valves to a high degree of accuracy.

A colloquial term used by a vehicle dealership where he takes the customer out of his trade-in and lets him temporarily drive a borrowed car from the dealership until his purchase is completed.
A device which absorbs moisture from the atmosphere. It can be a unit dedicated for this purpose, or even an air conditioner.
To remove water vapor from the air
Dehydrated oil
Lubricant which has had most of its water content removed (dry oil).
Small tank which serves as liquid refrigerant reservoir and which also contains a desiccant to remove moisture. Used on most automobile air conditioning installations.


To remove the ice from the outside of the windshield.
Deice control
Device for operating a refrigerating system in such a way as to provide melting of the accumulated ice and frost.
  1. A liquid or spray which is applied to the windshield to assist in removing ice.
  2. Material applied to roadways to prevent ice build-up or to melt ice.
The process of applying chemicals to the road surface to remove snow, ice, or frost after it has bonded to the pavement
De-ionized water
Water from which impurities have been removed by a special process and used for topping up batteries.
An old brand of automobile of which the 1925-1948 Model D-8, not 4-cyl. and the 1924-1926 GL and GLS Models with required application is a classic car. The 1946-49 D-6 Sedans are milestone cars.
An old brand of automobile of which the 1925-1948 Series 135, 145, 148, 165 (but not the 4-cyl.) with required application are Classic cars. The Type 135, 175, 180 (1946-51) are milestone cars.
To split a layered or laminated material into its separate layers. Sometimes used to describe failure of an adhesive in bond strength testing
Delaunay Belleville
An old brand of automobile of which the 1925-1948 6-cyl models are classic cars.
Delayed coking
A process by which heavier crude oil fractions can be thermally decomposed under conditions of elevated temperatures and pressure to produce a mixture of lighter oils and petroleum coke. The light oils can be processed further in other refinery units to meet product specifications. The coke can be used either as a fuel or in other applications such as the manufacturing of steel or aluminum.
Delay relay
Delay system
Delay vacuum bypass system
(DVB) an optional system used by Ford that bypasses the spark delay valve during cold operation to improve driveability
Delay valve
A valve used in a vacuum or hydraulic system in which the valve’s opening or closing is delayed. Also called Vacuum delay valve

Delay wiper
A windshield scraper which can be set to activate at various times and pauses between each swipe. It is useful when there is a mist or light rain. Also called intermittent wiper.


Delineator post

Delineator PostDelineator Post

A barricade marking device placed on a road to prevent travel in a particular direction

  1. To pump or discharge a liquid.
  2. To drive a new car from the factory to the distributor or dealer. Or to drive it to the customer.
Represents the number of future years during which a pipeline company can meet its annual requirements for its presently certificated delivery capacity from presently committed sources of supply. The availability of gas from these sources of supply shall be governed by the physical capabilities of these sources to deliver gas by the terms of existing gas-purchase contracts, and by limitations imposed by State or Federal regulatory agencies.
Delivered cost
The cost of fuel, including the invoice price of fuel, transportation charges, taxes, commissions, insurance, and expenses associated with leased or owned equipment used to transport the fuel.
Delivered gas
The physical transfer of natural, synthetic, and/or supplemental gas from facilities operated by the responding company to facilities operated by others or to consumers.
  1. The discharging of a liquid from a pump.
  2. Driving a new car from the factory to the distributor or dealer
Delivery lines
Fuel lines used to carry fuel from the fuel injection pump to the injector nozzles
Delivery mileage only
The odometer reading reflects only the distance from the factory to the selling dealer.
Delivery receipt
(DR) The control document used to deliver freight to the consignee. The delivery receipt is signed by the consignee and the driver. Also used as a receipt for collecting monies and for recording delivery exceptions.
Delivery valve
  1. The valve on the outlet side of a pump.
  2. A fuel injection pump valve that rapidly decreases injection line pressure to achieve an abrupt fuel cutoff at the injector
DeloreanClick image for books on

A model of automobile manufactured by John Z. DeLorean

Del Sol
Honda Del SolClick image for books on
Honda Del Sol

A model of automobile manufactured by Honda

Delta configuration
A triangular connection of the three stator windings of an alternator.

Delta cycle
A three wheel cycle with two wheels in back, one in front, sleekly elongated.

Delta transformer
Three-phase electrical transformer which has ends of each of three windings electrically connected to form a triangle.
(DL) A term used to indicate a series of vehicle which is just above the basic version.
A machine used to cut the lugs from tires prior to buffing.
Removing residual magnetism from an object which had been previously magnetized
Demand charge
a surcharge levied by an electric utility for unusual, short-term energy use.
Demand Management
Measures aimed at reducing private car usage.
Demand meter
Instrument which measures the kilowatt-hour usage of a circuit or group of circuits.
A British term to clear fog or frost from the windshield or rear window. In the US and Canada, the term is Defog.
A British term for a Defogger or Defroster
Short form for demonstration vehicle
Demonstration vehicles
Vehicles operated by a motor vehicle dealer solely for the purpose of promoting motor vehicle sales or permitting potential purchasers to drive the vehicle for pre-purchase or pre-lease evaluation; or a vehicle that is owned and operated by a motor vehicle manufacturer or motor vehicle component manufacturer, or owned or held by a university research department, independent testing laboratory, or other such evaluation facility, solely for the purpose of evaluating the performance of such vehicles for engineering, research and development, or quality control reasons. Also called Test Vehicle
A vehicle used by a dealer for test drives and sold later at a reduced price.

Demonstrator vehicle
Demountable flange
A side ring or side and lock ring combination that retains the tire on the rim. It is removable to permit tire mounting or removal.
Demountable rim
  1. A two piece wheel rim found on trucks. The main part of the rim remains on the axle while a side piece and a locking ring is removable. In this way the whole rim is not removed from the vehicle like a passenger car’s rim and wheel. Demountable rims are still in use, though they have been replaced in many applications by the simpler disc wheel.
  2. Multi-piece steel wheel rim assembly which is bolted to a spoke hub. Demountable rims are still in use, though they have been replaced in many applications by the simpler disc wheel. See Cast Spoke Wheel.
The resistance of oil to emulsification, or the ability of oil to separate from any water with which it is mixed. The better the demulsibility rating, the more quickly the oil separates from water
  1. The charge paid to the vessel owner or operator for detention of a vessel at the port(s) beyond the time allowed, usually 72 hours, for loading and unloading.
  2. Penalty for exceeding free time, usually 48 hours, allowed for loading/unloading under terms of railroad/ocean and motor carrier traffics.
Denatured alcohol
Ethyl alcohol made unfit for drinking by the addition of toxic or nauseating substances such as methanol, benzene, or pyridine. Used to clean a brake system.
Denovo tire
A special tire (fitted to a special rim) which used to be made by Dunlop, and which can be run flat for up to 160 km (100 miles) at up to 80 kph (50 mph)
  1. Compactness; relative mass of matter in a given volume.
  2. Closeness of texture or consistency of particles within a given substance. The weight per unit volume.
  3. The weight or mass per unit volume of a gas, liquid, or solid
  1. A hollow or dip in a body panel caused by a sharp blow or impact.
  2. To cause a dent in a body panel
Dent puller
Two types of tools used to pull out dents in body panels. One is a Suction cup dent puller and the other is Panel puller.
Dent puller slide hammer

Dent PullerSlide Hammer Dent Puller

A tool used to pull a dent in a panel back to shape.

Denver boot

Denver BootDenver Boot

A locking device which wraps around the wheel of a vehicle to immobilize its movement. Also called Wheel clamp

Device which absorbs or adsorbs various odors, usually by principle of absorption. Activated charcoal is commonly used.
The starting line of a Randonnée or Brevet
Department of Defense

Department of Energy
Department of Transportation
(DOT) The various U.S. federal agencies that regulate the operation of motor vehicles and motor vehicle equipment.
Departure angle
  1. The most sharply angled incline the vehicle can leave without its rear hitting the ground. As with approach angles, it’s formed on one side by the horizontal axis, and on the other by a straight line connecting the rear edge of the rear tire and the most prominent point at the rear of the vehicle, usually the bumper or exhaust pipe.
  2. In side view, the angle between the ground and a line, aft of the vehicle, joining the periphery of the rear wheel and (typically) the rear chassis member or other low component. It represents the size or steepness of a slope or obstacle that can be approached or climbed in reverse without striking bodywork.
Depleted storage field
A sub-surface natural geological reservoir, usually a depleted gas or oil field, used for storing natural gas.
Removal of residual magnetism thereby destroying or removing the magnetic. To remove polarity
  1. A coating of unwanted mineral or layer of sediment at the bottom of a tank.
  2. To apply a coating of something (often metal by electrolysis).
The loss of value of a vehicle because of age or deterioration
  1. An indentation or dent in the surface of a sheet of metal whether through deliberate design or accident.
  2. A restriction of airflow which causes low pressure and a partial vacuum.
Depression Regulator
Depress the accelerator
The action of pressing down on the gas pedal (accelerator) to cause more fuel to enter the engine thus making the vehicle go faster. Opposite to ease up on the accelerator.
Depress the gas pedal
The action of pressing down on the gas pedal (accelerator) to cause more fuel to enter the engine thus making the vehicle go faster. Opposite to ease up on the gas pedal.
Depress the throttle pedal
The action of pressing down on the throttle pedal (accelerator) to cause more fuel to enter the engine thus making the vehicle go faster. Opposite to ease up on the throttle pedal.
Abbreviation for Digital Engine Position Sensor
Depth gauge
A measuring tool for determining the depth of something.

Depth micrometer
A measuring device (micrometer) used for precise measurement of a hole depth, recesses, keyways, etc.
Depth of thread
The distance from the thread Crest to Root measured perpendicular to the axis of the thread
Depth Reclamation
Abbreviation for Delivered Ex Quay (Duty Paid) with the named port of the destination. The seller fulfills his obligation to deliver when he has made the goods available to the buyer on the quay (wharf) at the named port of destination, cleared for importation. The seller has to bear all risks and costs including duties, taxes and other charges of delivering the goods thereto.


A lever-activated mechanism that pushes the chain off one Sprocket of a bicycle and onto another, thus changing the Gear ratio.

Derailleur Braze on
Derailleur cable
A wound steel cable running from the shift lever to the derailleur on a bicycle.
Derailleur cable housing
The outer casing into which the inner wire is inserted. The inner wire of a brake cable and matching housing is thicker than those of a derailleur and thus are not compatible.
Derailleur chain, narrow width
A bicycle chain made especially for use on an ultra or narrow freewheel often recognized by bulging inner link plates and Flush chain pins.
Derailleur chain, standard width
A bicycle chain designed to fit a freewheel of standard width, usually characterized by straight-edged plates and chain pins that protrude slightly beyond the outer link plates.
Derailleur Clamp on
Derailleur hanger
The part of a rear dropout to which the rear derailleur attaches

Derailleur pulleys
One of two guide wheels of the rear derailleur which directs the path of the chain.
The elimination of some or all regulations from a previously regulated industry or sector of an industry.
Abbreviation for Diagnostic Energy Reserve Module
A device for hoisting and lowering heavy weights, cargo, stores, etc
To remove rust from a metal part
Diesel oil when used as a fuel for road vehicles. Abbreviation for diesel-engined road vehicle
Abbreviation for Delivered Ex Ship with the named port of destination. The seller fulfills his obligation to deliver when the goods have been made available to the buyer on board the ship uncleared for import at the named port of destination. The seller has to bear all the costs and risks involved in bringing goods to the named port of destination.
The desalter mixes the hydrocarbon stream with a small amount of fresh water (e.g. 10% by volume) forming a water-in-oil emulsion. The resulting emulsion is subjected to an electric field wherein the water is coalesced as an under flow from the upper flow of a relatively water-free, continuous hydrocarbon phase. The desalted hydrocarbon stream is produced at relatively low cost and has a very small residual salt content. The performance of this unit can be improved with a demulsifier, such as Alken 860 Demulsifier.
The removal of scale or metallic oxide from metallic surfaces by pickling
Descent Control
  1. A drying agent (silica gel or a similar substance) used in refrigeration or air conditioning systems to remove excess moisture from refrigerant vapor
  2. Substance used to collect and hold moisture in refrigerating system. A drying agent. Common desiccants are activated alumina and silica gel.
  1. The arrangement of parts or the form of construction.
  2. To arrange parts or construction of a vehicle or major component.
Design Gross Vehicle Weight
(DGVW) The manufacturers specifications of Gross Vehicle Weight
Design Horsepower
The specified horsepower for a chain drive multiplied by a service factor. It is the value used to select the chain size for the drive.
Design pressure
Highest or most severe pressure expected during operation. Sometimes used as the calculated operating pressure plus an allowance for safety.
A man who both figures and determines what kind of deal the dealership will make to a customer.
A man who both figures and determines what kind of deal the dealership will make to a customer.
Something (like valves) which is opened and closed by a mechanical device. In most 4-stroke engines the valves are opened by the cam, but closed by the action of the valve springs. In a desmodromic system, the valves are opened by a cam and closed by a cam or a cable. A desmodromic system is more costly and more difficult to manufacture, but the advantage is more precise control of the valves and less valve bounce which is seen in a normal engine at high speed.
The removal of material which has been adsorbed. It is the opposite of Adsorption.
De Soto
De SotoClick image for books on
De Soto

A vehicle brand of which the 1956-58 Adventurer models are milestone cars.

Trucker slang for road construction as in ‘Seem’s like all the roads in Pennsylvania are always under destruction.’
The removal of sulfur, as from molten metals, petroleum oil, or flue gases.
A component for removing sulfur from a fuel mixture.
Detachable rim
A wheel rim which is bolted to the wheel center or spider and can be disassembled for replacing the rubber tire. It is found on trucks and some quads. It is also called a Demountable rim
The action of correcting all appearance flaws in a vehicle.
A term coined by Art Treta to indicate a compulsive disorder which compels a vehicle owner to correct its every flaw to the extent that he searches for even the most hidden flaw.

Detector, leak
Device used to detect and locate refrigerant leaks.
Detent ball and spring
A Spring loaded ball that snaps into a groove or notch to hold some sliding object in position.
A charge made for a vehicle held by, or for, consignor or consignee for loading, unloading or for forwarding directions.
  1. A soap-like chemical added to the engine oil (particularly MS oil) or gasoline to improve its characteristics and keep the engine clean by controlling the formation of Sludge and gum as well as controlling foaming.
  2. Additives used to inhibit deposit formation in the fuel and intake systems in automobiles.
Detergent oil
An MS oil which keeps the engine clean by preventing the formation of sludge and gum. It keeps particles and contaminants in suspension and has the ability to neutralize acids resulting from the combustion process.
De Tomaso Pantera
De Tomaso PanteraClick image for books on
De Tomaso Pantera

A model of automobile manufactured in Italy

  1. The action of the fuel charge firing or burning too violently, almost exploding. It sometimes results in a noise called pinging. Detonation is caused by autoignition of the end gas i.e., that part of the charge not yet consumed in the normal flame-front reaction. Detonation occurs because piston motion and compression of the end gas raise its temperature and pressure to the point where the end gas autoignites. The pinging or knocking noise is the result of intense pressure waves in the charge which cause the cylinder walls to vibrate. Also called fuel knock.
  2. A violent explosion involving high-velocity pressure waves; in a gasoline engine, the spontaneous combustion of part of the compresses charge after spark occurs. Detonation usually produces a characteristic metallic sound, or knock.
  3. A condition where excessive temperature in the combustion chamber causes uncontrolled, explosive burning of the air-fuel mixture. As the detonated flame front collides with the flame front initiated by the spark plug, extreme pressure is often heard as pinging or knocking. Also see preignition.
Detonation-activated ignition retard
A system which retards the ignition timing when the detonation sensor picks up vibration at frequencies typical of denotation
Detonation Meter
Detonation sensor
A detection device, usually piezoelectric, mounted near the cylinders which can detect engine knocking or frequencies of detonation so that it will send a message to retard the ignition timing to prevent damage to the engine.
An alternative route which traffic has to follow due to closure of a stretch of road for repairs, etc. A diversion.
Detoxed vehicle
A vehicle with a reduced emission system consisting of a catalytic converter, EGR, air injection, fuel evaporative emission control, etc. Also called a controlled vehicle
The intentional adjustment of an engine to reduce its power in an attempt to reduce emissions, reduce top-end speed, increase fuel economy, or meet specific governmental standards.


  1. Hot rod built around a 1932 Ford Coupe body.
  2. A colloquial term used by vehicle dealers to refer to a $200.00 amount used for holding a vehicle, down payment, trade-in value, etc.
Deuterium Uranium Reactor
Deutsche Industrie Normen


Development well
A well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive.
Deviation angle
A piece of equipment or a mechanism designed for a specific purpose or function.



Cadillac De VilleClick image for books on
Cadillac De Ville

A model of automobile manufactured by the Cadillac division of General Motors. Two models were available: a sedan (1949-2005) and a coupe (Coupe de Ville) (1949-93). Sometimes spelled Deville.

DeVille extension
A sliding roof over the front seat with side arms that folded back into the remaining roof thus producing a Sedanca configuration in metal rather than the usual fabric.
A vehicle brand of which the 1958-62 S/S models are milestone cars.
Condensed atmospheric moisture deposited in small drops on cool surfaces.
To remove a coating of wax from the body of a vehicle usually in preparation for painting.
Dew point
Temperature at which vapor (at 100 percent humidity) begins to condense and deposit as liquid.
A coolant that raises the boiling point and lowers the freezing point of the water in the cooling system, prevents rust and corrosion, and lubricates the system components. It is often called long-life antifreeze. It is orange in color and is designed to function up to 60 months or 240,000 Kilometres.
Abbreviation for Diamond frame
Abbreviation for Digital frequency control
Abbreviation for Decel Fuel Cutoff Mode
Abbreviation for Direct Fuel Injection
Abbreviation for Deceleration Fuel Shutoff
Abbreviation for Defense Fuel Supply Center. Used by all branches of the Department of Defense (DOD)
Abbreviation for Diesel General oil for use under ordinary conditions in diesel engines.
Abbreviation for Design Gross Vehicle Weight


Abbreviation for Drophead coupe

  1. Abbreviation for direct ignition — a system where each spark plug has its own ignition coil, thus eliminating the need for a distributor
  2. Abbreviation for Distributor Ignition (System)
A two-lead alternating current semiconductor that allows current to flow in both directions at a preset voltage.
Refers to use of instruments to determine cause of improper function of parts or system of a vehicle

Diagnostic center
A garage or part of a garage where problems with a vehicle or part of a vehicle are determined.
Diagnostic code
  1. Code displayed on instrument panel which can be used to determine area in system where malfunction may be located.
  2. Code numbers obtained by accessing the diagnostic mode of the engine management computer. This code can be used to determine the area in the system where a malfunction may be located
Diagnostic computer
A computer terminal or engine analyzer which is hooked up to the car’s electronic box and reveals the condition of the engine and various sensors.
Diagnostic connector
Diagnostic link
The electric cord which connects the computer terminal to the socket on the vehicle.
The process of identifying the cause or nature of a condition, situation, or problem to determine the appropriate corrective action to take in the repair of an automotive system.

Diagnostic socket
A socket on the vehicle (usually found in the engine compartment) which is part of the onboard electronic sensor system.
Diagnostic system
The various sensors and electronic devices which record the operation of a number of functions within the vehicle.

Diagnostic testing
The analysis of the various functions of the components of a vehicle to determine if they are operating properly or have recorded faults which need to be corrected.
Diagnostic test modes
Various levels of diagnostic capabilities in OBD systems. These may include different functional states to observe signals, a base level to read diagnostic trouble codes, a monitor level which includes information on signal levels, bi-directional control with on/off board aids, and the ability to interface with remote diagnosis.
Diagnostic trouble codes
  1. A numeric identifier for a fault condition identified by the on-board diagnostic system.
  2. A number stored by the ECU when it detects a failure in a particular electrical circuit or mechanical system it is capable of monitoring. This number is a useful guide for repairing a problem.
Diagonal belt
Another term for Shoulder belt
Diagonal brake system
A dual brake system with separate hydraulic circuits connecting diagonal wheels together (right front to left rear and left front to right rear)
Diagonal cutting
Diagonal cutting pliers
Diagonal split braking system
A dual-circuit braking system in which each circuit brakes one front wheel and the diagonally opposite rear wheel, so that in the case of failure of one circuit reasonably balanced braking can be achieved.


Diagonally split system
A dual-circuit braking system in which each circuit brakes one front wheel and the diagonally opposite rear wheel, so that in the case of failure of one circuit reasonably balanced braking can be achieved.


Diagonal suspension
A manifestation occurring off-road when a vehicle is, for example, diagonally crossing a small but well-defined ridge. When the ridge is so severe that, say, the right front wheel and the rear left wheels are on full ‘bump’ (i.e., fully up in the wheel arches) and the other wheels are hanging down to the full extent of wheel travel, the vehicle may be described as being diagonally suspended or on diagonal suspension. Some also refer to this state as being cross-axled.
Diagonal wheel-spin
The wheel-spin that can take place on the fully extended wheels in a condition of diagonal suspension. However, a vehicle need not be in a totally diagonal suspension condition for diagonal wheel-spin to take place; minor off-loading of diagonally opposed wheels or the presence of slippery ground under these wheels can provoke the condition. Can also occur crossing ditches diagonally;.
The face (usually circular) of an instrument like a speedometer, tachometer, vacuum gauge, etc.

A service which enables mobility impaired people to pre-book door-to-door travel by bus. Also called handi-bus or handi-van
Dial bore gauge
A precision measuring tool which combines a telescoping gauge and dial indicator to give readings of inside diameter measurements.
Dial caliper

Dial CaliperDial Caliper

  1. A slide-type measuring device which registers on a dial the distance between two points
  2. A precision measuring tool used to determine inside, outside, or depth measurements. Measurements are displayed on a dial index.
Dialed in
  1. The action of fine tuning an engine or component to its peak capacity.
  2. The ideal set up of a bicycle when everything works just right
Dial gage
Dial gauge
A precision Micrometer type instrument that indicates the reading via a Needle moving across a dial face.
Dial indicator
A precision measuring instrument that indicates linear movement to a thousandth of an inch (.01mm) with a needle sweeping around a dial face.

Dial torque wrench

Torque WrenchTorque Wrench

A wrench usually with a socket end and which measures the torque of a nut-bolt fastener. It registers the value on a dial.

Having a magnetic permeability of less than one; material with this property are repelled by a magnet and tend to position themselves at right angles to magnetic lines of force.
The distance between one edge of a circular object to the other edge and passing through the center.

Diameter Brake Drum
Diamond frame

Bicycle frameBicycle frame

  1. The traditional men’s bicycle frame the principal parts of which form a diamond shape.
  2. Tubular-frame design for motorcycles common until WW II and derived from the bicycle layout. The engine cases often form part of the structure. In profile it resembles a diamond shape
Diamond star
The name of Chrysler Corporation which comes from the pattern of its emblem.
  1. A flexible cloth-rubber sheet that is stretched across an area thereby separating two different compartments. A diaphragm is used in pumps to create a pressure differential that causes a fluid to be pushed or pulled from one point to another. Some carburetors have no float bowl (i.e., Tillotsen), but use a series of diaphragms to pump gasoline into the engine.
  2. A flexible partition used to separate two chambers or elements.
  3. In air-conditioning system, a rubber-like piston or bellows assembly which divides the inner and outer chambers of backpressure regulated air conditioning devices.
  4. In fuel system, a thin dividing sheet or partition which separates a housing into two chambers, one of which is usually vented to vacuum while the other is not; used in vacuum-controlled secondaries, anti-stall dashpots, and other carburetor control devices.
  5. A rubber-like piston or bellows assembly which divides the inner and outer chambers of back-pressure regulated air conditioning devices
Diaphragm clutch
Another term for a Diaphragm spring clutch
Diaphragm Gasket
Diaphragm link
The arm which transmits the movement of the diaphragm and the distributor baseplate in a vacuum advance mechanism.
Diaphragm pump
A device which has a flexible diaphragm which moves forward and backward by a solenoid or other mechanical device to transfer fluid.

Diaphragm spring

Diaphragm SpringDiaphragm Spring

A slightly cone-shaped metal disc with tapering fingers pointed inward or like a wavy disc, used in some clutches. In an automotive clutch, the diaphragm spring is part of the clutch pressure plate. When the clutch is engaged, this spring is flattened and forces the pressure plate against the clutch disc; driver effort through the clutch linkage overcomes the spring pressure to disengage it.

Diaphragm spring clutch
Diaphragm ClutchClick image to supersize
Diaphragm Spring Clutch

A common clutch used in most vehicles with manual transmission where a diaphragm spring keeps the pressure plate in contact with the friction plate

Diaphragm Type Valve
A device consisting essentially of an automatic valve actuated by means of the application of fuel pressure upon a flexible diaphragm.
Diaphragm Valve
A device consisting essentially of an automatic valve actuated by means of the application of fuel pressure upon a flexible diaphragm.
Abbreviation for Driver Information Center
The chemical substance (CCl2F2) used in automotive air conditioning systems to absorb, carry, and release heat. A member of the fluorocarbon family. Usually referred to as refrigerant or R-12
British term for rumble seat, an external seat that could be accessed by lifting a forward opening ‘trunk-like’ lid in the rear of the car.
Abbreviation for Distributor Ignition Control Module


  1. One of a matched pair of hardened steel blocks that are used to form (by stamping, pressing, cutting, extruding, drawing or threading) metal into a desired shape.
  2. A tool for cutting external threads. Opposite of tap
  3. A tool for forming a rivet head (applied to rivet dies).
Die back


In a Lacquer Finish the loss of Gloss after compounding, caused by continued Evaporation of Thinner.
Die cast
  1. Manufactured by forcing molten metal into a die. Especially used of aluminum or an alloy.
  2. To form metal or plastic by pouring the molten substance into a mold and letting it solidify.
Die casting
  1. Formation of an accurate and smooth object by forcing molten metal, plastic, etc., into a die or mold under pressure.
  2. Process of molding low-melting-temperature metals in accurately shaped metal molds.
  3. A part formed by pouring a molten metal alloy, often bronze or zinc, into a mold.


Die Chaser
The separate individual cutting teeth units mounted in a large die head. Usually four or more units are installed. Some dies have these chasers permanently mounted while others are replaceable. The chaser cuts the external screw threads and is used to clean up damaged threads.
A material which is an electrical insulator or in which an electric field can be sustained with a minimum loss of power.
Dielectric fluid
Fluid with high electrical resistance.
Dielectric grease
A special grease which is applied to the ends of electric terminals to inhibit corrosion between the terminals or to be sure that there is good electrical contact between the terminals.
Dielectric silicone compound
A non-conducting silicone grease applied to spark plug wire boots, rotors, and connectors to prevent arcing and moisture from entering a connector
Die model
The master model, traditionally hand carved from mahogany that served as the final, correct guide for making sheetmetal stamping dies.
A type of engine or fuel or oil used for that engine.

Diesel cycle
A four-stroke cycle where the air is sucked into the cylinder and compressed at a ratio of up to 241. At the end of the compression stroke the fuel is injected. Because of the high compression and resulting increase in temperature, the fuel is ignited leading to the power stroke and followed by the exhaust stroke where the combustion products are removed.
Diesel-electric plant
A generating station that uses diesel engines to drive its electric generators.
Diesel engine
An internal combustion engine that uses diesel oil for fuel. The true diesel does not use a carburetor or an ignition system (i.e., spark plugs) but injects diesel oil into the cylinders when the piston has compressed the air so tightly that it is hot enough to ignite the diesel fuel without a spark. Because a cold engine cannot ignite the diesel fuel, Glow plugs are used to heat the mixture, but they do not provide a spark. Named after Rudolf Diesel (1858-1913), the inventor.

Diesel fuel
  1. A light oil fuel which has a relatively low ignition temperature. It is heavier than gasoline and uses the heat of extremely highly compressed air to ignite the fuel in the combustion chamber.
  2. A fuel composed of distillates obtained in petroleum refining operation or blends of such distillates with residual oil used in motor vehicles. The boiling point and specific gravity are higher for diesel fuels than for gasoline.
Diesel fuel system
Diesel engines are internal combustion engines that burn diesel oil rather than gasoline. Injectors are used to spray droplets of diesel oil into the combustion chambers, at or near the top of the compression stroke. Ignition follows due to the very high temperature of the compressed intake air, or to the use of Glow plugs, which retain heat from previous ignitions (spark plugs are not used). Diesel engines are generally more fuel-efficient than gasoline engines but must be stronger and heavier because of high compression ratios.
Diesel Fuel Testing Unit
Diesel index
Product of the API gravity and the Aniline point (in degrees Fahrenheit) of a Diesel fuel, divided by 100; an indication of the ignition quality of the fuel.
A form of autoignition in which a gasoline engine continues to fire after the ignition has been shut off. In late-model emission-controlled engines, dieseling or run-on is caused by heat and the unusually high Manifold pressure that result from retarding the spark at idle.
Diesel knock
The noise caused by the rapid rise in pressure in a diesel engine especially when the engine is cold or running at a low speed. Also called diesel rattle.


Diesel oil
Fuel for cars with diesel engines. This is not a form of lubricating oil.

Diesel Oxidation Catalyst
(DOC) Catalyst promoting oxidation processes in diesel exhaust. Usually designed to reduce emissions of the organic fraction of diesel particulates, gas-phase hydrocarbons, and carbon monoxide.
Diesel particulate filter
(DPF) A filter which removes small particles from a diesel exhaust. It looks like a honeycomb catalytic converter but acts as a mechanical separator. It prevents these particles from discharging in the tailpipe. Collected particulates need to be removed from the filter, usually by continuous or periodic oxidation in a process called regeneration.
Diesel Particulate Matter
(DPM) Sub-micron size particles found in diesel exhaust. Most emission regulations specify DPM measurement methods in which particulates are sampled on filters from cooled exhaust gas. The cooling causes condensation of vapors in the gas sampling train. Thus, the DPM is composed of both solid and liquid particles and is generally classified into three fractions:

  1. inorganic carbon (soot)
  2. organic fraction (often referred to as SOF or VOF)
  3. sulfate fraction (hydrated sulfuric acid)
Diesel rattle
Another term for Diesel knock
Die set
Die stock
A tool used to hold and operate dies when cutting outside threads.
Die size
Retread rubber is designated by its crescent shaped dimensions in inches and eighths, and its thickness in 32nds of an inch; (e.g., 66-72-16; the crown would measure 6 and 6 eighths, the base 7 and 2 eighths wide; and the thickness 16/32 of an inch, or gauge of the stock rubber.)
A colloquial term for a differential
Locking mechanism of the center differential on a four-wheel drive vehicle. In some vehicles, activation is made by moving the shift lever, by activating a separate lever, or by engaging a button (usually on the shift lever). Once engaged, the ‘DIFF-LOCK’ light on the instrument panel is illuminated. Engaging the diff-lock causes all four wheels to rotate alike giving good traction on slippery terrain. When the vehicle is driven on pavement, the center differential should be unlocked so that the front and rear differentials can permit the wheels to turn independently of each other as required, for instance, when turning a corner.
DifferentialClick image to supersize
  1. Amount added to or deducted from the base rate to make the rate to or from some other point or via another route.
  2. The temperature or pressure difference between cut-in and cut-out temperature or pressure of a control.
  3. A unit on rear-wheel drive vehicles that takes the power of the rotating driveshaft at right angles to the rear axle and passes it to the axle. It will not only drive both rear axles at the same time, but will also allow them to turn at different speeds when negotiating turns. In this way the tires do not scuff or Skid
  4. In front-wheel drive cars, the differential is located in the transaxle, usually directly below the transmission.
  5. A mechanism that allows torque to be applied to two different gears that can turn at different speeds. In negotiating a corner, the outside wheel of a car must travel farther than the inside wheel in the same amount of time.
Differential cage
The rotating metal container inside the Differential housing and encloses the differential side gears and pinion gears. Also called the Differential carrier
Differential carrier
Differential case
The steel unit to which the Ring gear is attached. The case drives the Spider gears and forms an inner bearing surface for the axle and gears.
Differential casing
The Differential housing. It is the lowest point under a vehicle.
Differential gear
Differential gears
The gears that transmit engine power to the driving axles and are arranged so as to permit the rear wheels to turn at different speeds as required when the vehicle is negotiating a turn.
Differential grease
Differential housing

Differential housingDifferential housing

The enclosure which contains the Differential gears.

Differential lock
A mechanism which eliminates the action of the differential so that both wheels can be driven for better adhesion on slippery surfaces.
Differential pinion
The bevel pinion in the differential.
Differential pressure
  1. The pressure difference between two regions, such as between the intake manifold and the atmospheric pressures. In Bosch KE-Jetronic systems, the difference between actuator fuel pressure in the lower chambers of the differential-pressure valves and the system pressure entering the pressure actuator.
  2. The difference in pressure between the upper and lower chambers of a CIS fuel distributor
Differential pressure regulator

  1. A pressure actuator
  2. An electronically controlled valve which regulates the fuel flow to the lower chamber of the CIS fuel distributor
Differential pressure valve
Inside the Bosch CIS fuel distributor, these valves (there is one for each cylinder) maintain a constant pressure drop at each of the control-plunger slits, regardless of changes in the quantity of fuel flow
Differential pressure warning switch assembly
A unit to actuate a warning device indicating an undesirable pressure difference between the separate circuits of a brake system
Differential Sensor
Differential side gear
The bevel gear on either side of the differential into the center of which the axle shaft fits
Differential switch
Differential Valve
Differential Warning Switch
A projection in the base of the carburetor venturi and at the top of the needle jet that aids in fuel atomization.

Diffusing lens
The lens in the headlight glass which helps to focus the beam
  1. The way in which innovations spread through market or non-market channels.
  2. Mixing the molecules of two gases by thermal agitation
  3. Movement of a species under the influence of a gradient of chemical potential (i.e. a concentration gradient).
Diffusion Tube
Method of monitoring local air quality.
Diffusive transport
The process by which particles of liquids or gases move from an area of higher concentration to an area of lower concentration.
VW collaborated with Bosch to develop this electronic injection system. Digifant is similar to a Motronic system, except that its timing control map is less complicated than the Motronic map. And it does not have a knock sensor
Digifant II
A refined version of VW ‘s digifant. This system has some control improvements and uses a knock sensor for improved timing control
A signal that is either on or off. In a computer, the signal is translated into binary digits 0 and 1 and is interpreted by the microprocessor as a voltage signal that is either low or high, or current flow that is on or off.
Digital caliper
A slide-type caliper which gives a digital readout.
Digital clock
A timing piece which reveals the time with a series of numbers rather than with sweeping pointers.
Digital computer
A computer that works with information in the form of fixed numbers, usually in binary code.
Digital Control
Digital display
Instrument display that uses a liquid crystal display (LCD) for engine and vehicle speed as well as other indicators. Contrast Analog display
Digital filter
Electrical filter suitable for use with digital signals, i.e., those which are continuous with time. Contrast with Analog filter.
Digital frequency control
(DFC) A system which automatically stabilizes or tunes the frequency of a selected radio station.
Digital fuel injection
(DFI) a GM system, similar to earlier electronic fuel injection system, but with digital microprocessors. Analog inputs from various engine sensors are converted to digital signals before processing. The system is self-monitoring and self-diagnosing. It also has the capabilities of compensating for failed components and remembering intermittent failures
Digital gauge
A measuring tool which displays information in a digital format. Digital displays can use liquid crystal display (LCD), light-emitting diode(LED), etc.
Digital ratio adapter controller module
(DRAC) a device used on GM vehicles to convert the analog signal from the speed sensor into a digital signal that the EBCM can use
Digital speedometer
A speedometer which shows the speed in digital numbers rather than a needle on a dial gauge (which is called an analog speedometer).
Digital volt-ohm multimeter
(DVOM) a digital electronic meter that displays voltage and resistance
Dig out
To accelerate at top power.
A fluid which thins or weakens another fluid.
Dilution air
Air which enters a Draft regulator or similar device and mixes with the flue gases.
Dimethyl Ether
(DME) The simplest ether CH3-O-CH3. Can be manufactured from natural gas or from a renewable organic feedstock. DME is a prospective alternative diesel fuel.
A switch used to lower or dip the headlights from high beam to low beam and back again. In older cars it was located on the floor to the far left of the pedals. Most today are found on the signal arm.

Dimmer control
A rotary control switch which will increase or decrease the intensity of the instrument lights. Also called interior dimmer light switch.
Dimming mirror
A vehicle mirror located within the passenger compartment above the windshield which can be switched to reduce the glare from the headlights of a vehicle approaching from behind. Some are activated automatically while others are engaged by a lever below the mirror.
Dimmer switch
A device used to lower or increase the brightness and focus of the headlights (i.e., from high-beam to low-beam). The British term is dipswitch. Also called Headlight dimmer switch
Abbreviation for Deutsche Industrie Normen (German industrial standards). DIN horsepower is similar to the SAE net horsepower. It is measured at the Output shaft of an engine fully equipped with normal accessories.
A small dent in the surface of a panel
The action of straightening a damaged panel by using a hammer and dolly to bring it back into shape.
A colloquial term for a person who repairs body panels. A person who works in an automotive factory adjusting panels without damaging the paint
DIN mounting
The standard hole in the instrument panel through which a DIN radio can be installed
Ferrari DinoClick image for books on
Ferrari Dino

A model of automobile manufactured by Ferrari

A registered trade name by 3M for a thin, highly flexible, stretchable, paintable plastic film used to cover clay models to give them color and gloss. Di-Noc can be painted after adding an elasticizer. Painted, it’s usually soaked in a hot-water solution to make it pliable. The name Di-Noc also refers to an ornamental film used in the 1930’s through the early 1950’s to bond woodgrain and other ornamental patterns to garnish moldings, instrument panels, station-wagon exteriors, etc.
DIN radio
An aftermarket radio which fits into a thinner hole than most American radios. When installing a replacement radio, special faceplates are necessary
  1. Two-element electron tube which will allow more electron flow in one direction in a circuit than in the other direction; tube which serves as a rectifier.
  2. An electrical component having the ability to pass electric current readily in one direction but resisting current flow in the other. When four diodes are connected in a certain way (i.e., bridged) they will convert AC to DC, thus becoming a rectifier.
Dion axle
Dioxide Equivalent
Dioxide Laser
  1. A British term for dimming the headlights.
  2. A low lateral indentation of the pavement which may cause a speeding vehicle to lose control.
  3. To immerse.
Dipped beam
A British term for low beam
A British term for the Dimmer switch
Dipper switch
A British term for the Dimmer switch
Dipping mirror
A British term for Day-night mirror
  1. The metal rod that passes into the oil sump it is used to determine the quantity of oil in the engine. The oil level is marked on the rod and matches level indicators on the rod. Dipsticks are used to check engine oil and Transmission fluid. In most instances, the dipstick is inserted as far as it will go and then removed to check the level. In motorcycle engines, the dipstick is placed on the top of the threads (i.e., not screwed down) to check the level.
  2. A stick that’s dipped into a reservoir to check the level of the fluids based on the markings on the stick. Most common dipsticks are for used to check oil, transmission fluid, and power steering fluid.
A British term for the Dimmer switch
Dip treatment
Direct-acting shock absorber
A telescopic shock absorber.
Direct bearing lubrication
An oil injection system which feeds undiluted oil to two-stroke engine main bearings and rod big-end bearings.
Direct current
(DC) An electric current that flows steadily in one direction only. This is the type of current found in a battery and throughout the lighting and accessory system of a vehicle. Contrasts with Alternating current (AC).
Direct current motor
An electric motor which is energized by direct-current to provide torque. There are several classes of direct-current motors. The designer chooses the type to yield the desired characteristics.
Direct damage
A vehicle damage caused directly by an impact with an object. In contrast with an indirect damage.
Direct digital control
(DDC) Use of digital computer to perform required automatic control operations in a total energy management system.
Direct drive
When the Gearing is such that the crankshaft and driveshaft revolve at the same speed, the vehicle is in direct drive. Usually this occurs in High gear (except for those with Overdrive). It is represented as 1.001 ratio.
Direct drive powertrain
A system of propulsion where the speed of the engine, transmission, and propeller shaft rotate the same.
Direct drive transmission
Power is transferred from the clutch to the input shaft (mainshaft), to the countershaft (i.e., layshaft) and the high gear pinion, which holds the output sprocket.
Direct expansion evaporator
Evaporator using either an automatic expansion valve (AEV) or a thermostatic expansion valve (TEV) refrigerant control.
Direct ignition

  1. A system where each spark plug has its own ignition coil, thus eliminating the need for a distributor
  2. In diesel engines with direct injection the combustion chamber is not divided and fuel is injected directly to the cylinder.
Direct ignition device
An igniter used to ignite gas at a main burner.
Direct ignition system

  1. An ignition system which does not used a distributor but carries high voltage from the ignition coils directly to the spark plugs.
  2. A system in which the ignition means functions to ignite the main burner gas directly and in which a flame sensing means or safety shutoff device senses main burner flames or the absence of main burner flames.
Direct injection
A fuel injection system which is generally used in diesel engines and forces fuel directly into the combustion chamber. It requires very high injection system pressure to overcome the pressure within the combustion chamber.

Direct internal reforming
Production of a desired product (hydrogen) within a fuel cell from a hydrocarbon based fuel (methanol, gasoline, etc.) fed to the fuel cell or stack.
Directional baffle plate
Installed in a Quadrajet carburetor’s secondary bores to help direct the airflow for improved distribution in the intake manifold
Directional stability
Ability of a vehicle to move forward in a straight line with a minimum of driver control. A vehicle with good directional stability will not be unduly affected by side wind, road irregularities, etc.
Directional tire
Directional designs are recognized by the grooves in the tread that swipe away in a backward angle from the center of the tread face and rotate in only one direction. A direction of rotation arrow is located on both sidewalls of the tire. Directional tires enhance straight-line acceleration, provide maximum dry traction, better wet performance which helps to reduce rolling resistance as well as providing shorter stopping distances.

Directional tread
An arrangement of bars, grooves, and ribs on a tire’s tread in any manner that gives most effective traction when the tire revolves in only one direction.

Direction Finding
Direction indicator
The signal lights which blink on either side of the front of the vehicle and either side of the rear of the vehicle. Some early cars (like the Austin and Flying Standard) had small illuminated arms that flipped out from the B-post instead. The purpose of signal lights is to warn other drivers of a change in direction when turning a corner or changing lanes.
Direction indicator warning light
A light on the instrument panel which flashes when the signal lights are operating. Usually this light is in the shape of a green arrow. On some cars, like Cadillac, a secondary light is mounted in a pod on the upper edge of each front fender and in a pod inside the cab above the backlight (i.e., back window)
Direction of rotation
The direction in which a wheel or shaft turns or is supposed to turn.
Direction of travel
The direction in which an object (e.g., a vehicle) is moving.
Direct Loading
Loading of shipments directly from one service center to another without an intermediate stop for rehandling.
Direct methanol fuel cell
(DMFC) A type of fuel cell in which the fuel is methanol (CH3OH), in gaseous or liquid form. The methanol is oxidized directly at the anode with no reformation to hydrogen. The electrolyte is typically a PEM.
Direct polarity
Direct current flowing from anode (base metal) to cathode (electrode). The electrode is negative and the base metal is positive.
Direct-pull brake
A type of a very powerful centerpull bicycle brake used mostly on mountain bikes from the 1980s and early 1990s
A motorcycle intended for off-road use that are not legal to ride on public roads. Sometimes the term pure-dirt is used to distinguish a dirtbike from a dual-sport motorcycle
Dirty town
Trucker slang for New York City as in ‘I got a load of garbage going to dirty town.’
  1. An abbreviation for Direct ignition system or a distributorless ignition system similar to the C3I system, using two coils on four-cylinder engines
  2. Abbreviation for Direct Ignition (Waste Spark)
  1. The condition of a vehicle which is not able to be driven because of a failure of some component (e.g., bad battery, flat tire, engine seized) or because of an accident.
  2. A driver who lacks the use of a limb.
To take a vehicle or major component (e.g., the engine) apart in order to repair or restore the vehicle or component or to sell or recycle them. Also called dismantle.
May be spelled disk.

  1. A flat dish-shaped item which may or may not have a center hole.
  2. A parallel-faced rotating component of a disc brake system acted upon by brake pads to slow or stop the vehicle. Also called a rotor
Discard diameter
  1. The diameter at which a worn brake drum should be replaced
  2. The largest inside diameter at which a brake drum can safely operate.
Discard thickness
The thickness at which a brake disc should be replaced
Disc brake
Disc BrakeClick image to supersize
Disc Brake

A type of brake that has two basic components a flat rotor (disc) that turns with the wheel and a caliper that is stationary. When the brake pedal is depressed, linkage (mechanical or hydraulic) causes the caliper to force its heat-resistant brake pads against both sides of the rotating disc thus slowing or stopping the wheel. Almost all new cars have disc brakes on the front wheels with drum brakes on the rear. More expensive cars have four wheel disc brakes. Because of the need for greater pressure to activate disc brakes, most cars so equipped also have a power Booster. Wear takes place in the pads and the rotors. The pads are usually replaced while the rotors can sometimes be reground else they too must be replaced. If the rotors are not tightened correctly when installed, they can warp and cause a jerking motion when stopping.

Disc brake gauge
A tool for measuring the thickness, wear, and score depth on brake discs
Disc brake pad
An assembly consisting of friction material and its steel backing
Disc brake rotor
Disc brakes
Disc clutch
  1. The action of drawing electric current from the battery. The opposite action to charging.
  2. To pour out liquid from a pump.
  3. The product (e.g., the liquid) that is poured out of a pump.
  4. To bleed some or all of the refrigerant from a system by opening a valve or connection to permit refrigerant to escape slowly
Discharge air
Air conditioning air forced through the vents (ducts) into the passenger compartment
Discharge check ball
In a carburetor, a small check ball that lifts off its seat when the pump well is pressurized by the accelerator pump, which allows fuel to be discharged into the venturi through the shooter nozzle
Discharge controller
Discharged battery
A battery that cannot produce sufficient power.
Discharged Fuel
Discharge headlight
Discharge Hole
Discharge indicator
Discharge lamp
Discharge light
Discharge line
  1. In an air conditioning system, the line which connects the compressor outlet to the condenser inlet
  2. The line which connects the compressor outlet to the condenser inlet
Discharge nozzle
In a carburetor, the end of the main delivery tube that discharges fuel into the venturi area.

Discharge pipe
The outlet pipe from a pump
Discharge Ports
Discharge pressure
  1. The pressure exerted in a liquid pumped, expressed in psi.
  2. The (high side) pressure of the refrigerant being discharged from the air conditioner compressor
Discharge rate
Amount of current discharged from a battery, expressed in amps
Discharge side
  1. Outlet side.
  2. The part of the air conditioner system under high pressure, extending from the compressor outlet to the thermostatic expansion valve/tube inlet
Discharge terminal
Solderless connectors in male and female forms, intended to be easily disconnected and connected. Typically, a blad or pin (male connector) fits into a matching receptacle or socket (female connector). Many components have built-in (blade) terminals that require a specialized female connector.
Discharge valve
  1. Valve on the outlet side of a reciprocating pump. The opposite is suction valve.
  2. In an air conditioner system, a device used to check high side pressures, usually referred to as the high side service valve
  3. A device used to check high side pressures. Usually referred to as the high side service valve
Discharging current
Current supplied by a storage cell or battery, whose direction is opposite to that of the charging current
To alter the color of (a finish, metal, etc.) to a color which is not wanted. This fading may be caused by sitting in the sun, drops of contaminants (tree sap, bird dropping, spilled gasoline), poor paintwork, etc.
To remove the terminal from a mechanical or electrical device or from the other side of the terminal. While some may be simply pulled apart, others have catches which must first be released.
Disconnect terminal
Solderless connectors in male and female forms, intended to be easily disconnected and connected. Typically, a blade or pin (male connector) fits into a matching receptacle or socket (female connector). Many components have built-in (blade) terminals that require a specialized female connector
Disconnect the battery
The action of removing the high tension electrical cables from the battery terminals. Also called isolate the battery
A variety of small or large disfigurations on an object such as pits, tool marks, voids, overlaps, folds, seams, and inclusions.
Discontinuity of rolling contact
Generic term for wheel-spin and wheel slide – as on locked brakes. See Continuous rolling contact
Difference in rates not justified by costs.
Disc runout
A condition in which the disc is no longer parallel and does not rotate in a true circle. Usually due to excessive heat, which warps the disc.
Disc sander
A round, rubber disc powered by an electric drill and covered with abrasive paper for rough sanding work.

Disc type
Disc valve
A type of rotary valve that allows the passage of fluid through an arc-shaped slot.

Disc wheel
  1. A wheel constructed of stamped steel.
  2. A rim and metal disc that have been welded together. The disc is usually offset from the centerline of the rim to allow for dual tire mounting and to provide sufficient clearance between the duals. Disc wheels are attached to the hub with either single nuts or double cap nuts.
  3. Single-piece rim/wheel assembly of stamped and welded steel or forged aluminum, anchored by 8 or 10 nuts to a hub.
  4. A steel wheel whose center is stamped on one piece.
Disc wheel type
A type of dual mounting wheels where the discs are offset from the centerline of the rim to provide clearance between the tires. They are held in place by Double cap nuts, Inner cap nuts, and Outer cap nuts.
To move (a gear, dog clutch, etc.) so that it no longer meshes with another matching part
Disengage the clutch
During normal driving, the power of the engine is being transferred to the gears of a manual transmission because the clutch plates are pressed together. When you press down on the clutch pedal (or pull in the clutch lever on a motorcycle), you are releasing that contact (i.e., disengaging the clutch) so that there is no connection between the engine and the transmission. You engage the clutch when you release the pedal or lever.
  1. A depression in the top of a piston.
  2. Offsetting of the hub on a rear wheel on a derailleur bike to make room for the freewheel and still allow the wheel to be centered within the frame.
A plate, washer, or disc is dished when the center is recessed from the rim like a shallow bowl.
Dished brake disc
A disc that has worn thinner at the inner part of its friction surface. This is an abnormal form of wear
Dished rotor
A brake rotor that is thinner at the inner edges of its friction surfaces. Dishing is a form of taper variation
Dish washer
A washer is a flat disc with a hole in the center. The disc in a dish washer is dished or bent in a concave fashion.
Disintegration Energy
More commonly spelled disc.
To take a vehicle or major component (e.g., the engine) apart in order to repair or restore the vehicle or component or to sell or recycle them. Also called disassemble.
Dispersing or scattering in various directions; a state of matter in which finely divided particles of one substance (disperse phase) are suspended in another (dispersion medium) substance
Dispersion Formula
  1. The total volume of air displaced by all the pistons in traveling from BDC to TDC, i.e., the total volume of air and fuel the cylinder can hold before compression occurs. Also called Piston displacement.
  2. The total weight of the ship when afloat, including everything on board, (equals weight of water displaced.) Usually expressed in long tons.
Displacement compressor
Displacement, piston
Volume obtained by multiplying area of cylinder bore by length of piston stroke.
Displacement Pump
Displacement taxes
A vehicle taxation system which determines the amount of taxes based on the engine displacement of the vehicle.
Displacement volume
That part of the cylinder capacity that is swept by the pistons on their up and down strokes (i.e., the volume through which a piston moves in one stroke) formed by the bore diameter and the piston stroke. Also called swept volume.
Any device that conveys information. In a vehicle, displays are either lights, gauges, or buzzers. Gauges may be analog or digital

Display Case
Display unit
Disposition fee
A fee you pay at the end of the lease, to the lessor, that covers the lessor’s cost of getting the vehicle ready for sale after you have returned the vehicle. It is often applied against any deposit you made at lease inception.
Scattered in various directions
Transition from one scene to another in which the whole image of the first gradually disappears as it is replaced by the second
Distance piece
A collar or spacer which is placed between two parts to keep them the correct distance apart.
Distance to the sun
Distance traveled
A product formed by heating a liquid in a vessel and collecting and condensing the resulting by-product(s).

Distillate fuel oil
A general classification for one of the petroleum fractions produced in conventional distillation operations. It includes diesel fuels and fuel oils. Products known as No. 1, No. 2, and No. 4 diesel fuel are used in on-highway diesel engines, such as those in trucks and automobiles, as well as off-highway engines, such as those in railroad locomotives and agricultural machinery. Products known as No. 1, No. 2, and No. 4 fuel oils are used primarily for space heating and electric power generation.

  1. No. 1 Distillate: A light petroleum distillate that can be used as either a diesel fuel (see No. 1 Diesel Fuel) or a fuel oil. See No. 1 Fuel Oil.
    1. No. 1 Diesel Fuel: A light distillate fuel oil that has distillation temperatures of 288°C at the 90-percent point and meets the specifications defined in ASTM Specification D 975. It is used in high-speed diesel engines, such as those in city buses and similar vehicles.
    2. No. 1 Fuel Oil: A light distillate fuel oil that has distillation temperatures of 204°C at the 10-percent recovery point and 288°C at the 90-percent point and meets the specifications defined in ASTM Specification D 396. It is used primarily as fuel for portable outdoor stoves and portable outdoor heaters.
  2. No. 2 Distillate: A petroleum distillate that can be used as either a diesel fuel or a fuel oil.
    1. No. 2 Diesel Fuel: A fuel that has distillation temperatures of 260°C at the 10-percent recovery point and 338°C at the 90-percent recovery point and meets the specifications defined in ASTM Specification D 975. It is used in high-speed diesel engines, such as those in railroad locomotives, trucks, and automobiles.
    2. Low Sulfur No. 2 Diesel Fuel: No. 2 diesel fuel that has a sulfur level no higher than 0.05 percent by weight. It is used primarily in motor vehicle diesel engines for on-highway use.
    3. High Sulfur No. 2 Diesel Fuel: No. 2 diesel fuel that has a sulfur level above 0.05 percent by weight.
    4. No. 2 Fuel oil (Heating Oil): A distillate fuel oil that has distillation temperatures of 204°C at the 10-percent recovery point and 338°C at the 90-percent recovery point and meets the specifications defined in ASTM Specification D 396. It is used in atomizing type burners for domestic heating or for moderate capacity commercial/industrial burner units.
  3. No. 4 Fuel: A distillate fuel oil made by blending distillate fuel oil and residual fuel oil stocks. It conforms with ASTM Specification D 396 or Federal Specification VV-F-815C and is used extensively in industrial plants and in commercial burner installations that are not equipped with preheating facilities. It also includes No. 4 diesel fuel used for low- and medium-speed diesel engines and conforms to ASTM Specification D 975.
  1. Gasoline contains various hydrocarbons that boil at different temperatures. As a result, the gasoline boiling range can extend from 27°C to a maximum of 225°C. This is in contrast to water that boils only at 100°C at sea level.
  2. The process of heating a liquid to its boiling point and condensing and collecting the vapors
Distillation Curve
The percentages of gasoline that evaporate at various temperatures. The distillation curve is an important indicator for fuel standards such as volatility (vaporization).
Distillation unit
Distilled water
Pure water that through Distillation has had all other chemicals (salts, suspended solids, and organisms) removed. It is recommended for topping up batteries and radiators.
Distilling apparatus
Fluid-reclaiming device used to reclaim used refrigerants. Reclaiming is usually done by vaporizing and then recondensing refrigerant.
A warpage, bending, twisting, or change in form from the original shape.

Distortion Unit
Distribution calculation
Distribution Center
Distribution Centers are warehouse facilities that store, manage, and ship inventory on behalf of its clients. Inbound carriers bring product into the Distribution Center. Product can be immediately allocated to existing orders, or it can be placed into storage for the purpose of filling future orders. Outbound carriers transport stock from the Distribution Center to the end user. Distribution Centers are strategically placed close to major transportation lanes (i.e., highways, railroads). They rely on outside carriers as well its own fleet of trucks to transport product.
Distribution channel
The path goods take as their title transfers from producer to consumer. The title transfer for consumer goods is usually accompanied by transfer of the physical goods, as well.
Distribution controls
Systems which help evenly and efficiently transfer the heating or cooling medium to the area where it is needed.
Distribution factor
A calculation of the emf in the windings of an ac motor while taking into account that each coil is not in phase with the other coils.
Distribution System
See Closed Distribution System.
Distribution tube
Distribution tubes
Tubes used in the engine cooling area to guide and direct the flow of coolant to vital areas.
DistributorClick image to supersize
  1. A unit in the ignition system designed to make and break the ignition Primary circuit and to distribute the resultant high voltage to the proper cylinder at the correct time. The high voltage comes from the coil to the center terminal of the distributor cap and passes down the rotor. As the rotor turns, contact is made with each successive terminal on the circumference of the distributor cap. From there, the voltage goes into the spark plug wires and to the spark plug. Generally when your vehicle has its timing adjusted, it is the distributor that is adjusted. Also called ignition distributor.
  2. A distributor performs many of the same functions as wholesalers such as selling, physical distribution, credit, etc.; but is between the dealer and the wholesaler. Some industries use the term distributor instead of wholesaler.
  3. A company primarily engaged in the sale and delivery of natural and/or supplemental gas directly to consumers through a system of mains.
Distributor baseplate
The fixed plate in the body of the distributor on which the contact breaker or triggering device is mounted, and through the center of which the distributor shaft passes
Distributor body
The bowl-like part containing the distributor shaft with the rotor arm at its top end, and, in the conventional version, the centrifugal advance mechanism and the contact breaker
Distributor cam
The cam at the top of the distributor shaft with as many lobes as there are cylinders, acting on the heel of the contact breaker arm
Distributor cap

Distributor capDistributor cap

An insulated cover containing a central terminal or tower with a series (one per cylinder) of terminals or towers that are evenly spaced in a circular pattern around the central terminal or tower, the secondary voltage travels to the central terminal or tower where it is then channeled to one of the outer terminals or towers by the rotor. The cap also keeps dirt and moisture out of the distributor.

Distributor clamp
Distributor drive gear
A gear attached to the distributor shaft that meshes with a gear on the camshaft to cause the shaft in the distributor to turn.
Distributor hold-down clamp
A metal bracket at the base of the distributor that has a nut or bolt which can be loosened to allow the distributor to be moved on its shaft to readjust ignition timing or to open the points for Gapping.
Distributor injection pump
A fuel injection pump using pistons which pressurizes fuel for injection in the proper cylinder based on the relative port position of the rotating shaft in the hydraulic head
Distributorless ignition system
(DIS or DLS) An electronic ignition system that does not have a conventional rotating distributor. Instead, it uses multi-spark ignition coils or one ignition coil for each spark plug.
Distributor pipe
A pipe or tube through which the fuel travels from the fuel distributor to the injection nozzle
Distributor rotor
A rotating part of the distributor which transfers high voltage to each spark plug. In a distributors with points, it is oblong-shaped; but in a distributors without points, it is usually a disc. Also called a rotor or rotor arm.
Distributor shaft

Distributor ShaftDistributor shaft

The metal shaft inside the distributor that has a cam wheel which revolves with the shaft and forces the points to open. A spring causes the points to close. The distributor rotor is mounted on the top of this shaft.

Distributor tower
The terminals at the top of the distributor cap into which the spark plug wires fit. Also called terminal tower
Distributor weight
One of two flat pieces of metal found inside the distributor’s centrifugal advance mechanism on the baseplate. They swing out as speed increases and consequently advances the timing of the spark.
Distributor wrench
A special tool used to tighten or loosen the distributor hold down clamp when installing or removing a distributor
District heating and cooling
Use of a central utility system designed to provide heating and cooling to large residential and industrial areas.
An open channel for the passage of waste water along the side of the road

Ditch Witch
Brand name of a machine which digs trenches.
The action of the front of the vehicle to point downward (or dip) during braking. The opposite is Squat.

Moving apart. For example, traffic taking a right turn when other traffic is moving straight ahead or traffic leaving a motorway.
In today’s market, especially in smaller centers, a dealership cannot make a profit on just one brand of vehicle — especially foreign imports. Thus the dealership will diversify by having several brands (e.g., Mercedes-Benz, BMW, and Mazda). A car manufacturer diversifies by making several different kinds of vehicles (trucks, vans, luxury cars, family-size cars, commuter cars, compacts, convertibles, sports cars, etc.) in an attempt to reach every segment of the population. Some dealers or manufacturers may diversify by offering lawnmowers, boat motors, and motorcycles as well as automobiles (e.g., Honda) or even musical instruments (e.g.,Yamaha).
  1. An alternative route which traffic has to follow due to closure of a stretch of road for repairs, etc. A detour.
  2. A change made in consignee, destination, or shipment route while in transit.
To cause (air, a liquid, traffic, etc.) to follow a different course. For example, air is diverted to the air cleaner; traffic has been diverted around the accident site.
Diverter Solenoid
Diverter valve
  1. A valve which adds an amount of air to the rich air-fuel mixture entering the intake manifold during deceleration.
  2. Used in air injection system to channel airflow to either the exhaust manifold or oxidation catalyst under different operating conditions.
Divided highway
A high volume highway with a median that separates lanes of traffic going in opposite directions. Usually two or more lanes in each direction. Called dual carriageway in the U.K.
Divided propeller shaft
A propeller shaft, usually in long chassis rear-wheel drive vehicles, which is divided into two sections with a bearing and CV joint mounted on a chassis crossmember at the central point. Also called divided propshaft
Divided propshaft
A propeller shaft, usually in long chassis rear-wheel drive vehicles, which is divided into two sections with a bearing and CV joint mounted on a chassis crossmember at the central point. Also called divided propeller shaft
A measuring tool with two straight pointed arms used to mark off and transfer measurements, e.g., on sheet metal or other metal components.

Divorced choke
Vacuum diaphragm is mounted on the carburetor, but the bimetal spring is mounted either on a pad on the intake manifold or in a heat well in the exhaust man. Choke lever is operated by a mechanical linkage rod from the bimetal spring. Also called a Remote choke
An abbreviation for Do-it-yourself.

DIY mechanic
A person, whether qualified or not, who does his own repairs on his own vehicle.


Term used by Bosch to describe a fuel injection system controlled by manifold pressure. The D is short for druck, the German word for pressure. Manifold pressure is measured to indicate engine load (how much air the engine is using.) This pressure is an input signal to the control unit (ECU) for calculation of the correct amount of fuel delivery


In 1904 Jörgen Skafte Rasmussen set up on his own as a manufacturer of boiler fittings. In 1906 he purchased a textile mill in Zschopau, Saxony. Production started there in 1907. During the First World War Rasmussen worked on a steam-driven vehicle (Dampfkraftwagen), from which the three letters DKW were derived. In 1922 the company Zschopauer Motorenwerke started manufacturing its own motorcycles. The sporting successes of the lightweight motorcycles with 2.25 hp two-stroke engine were remarkable. Victories in the Berlin Avus race in 1922 and the triple victory by the DKW team in the ADAC Reichsfahrt the same year made people sit up and take notice. The first DKW motorcycle was consequently called the Reichsfahrt. Over the next six years Zschopauer Motorenwerke/DKW established itself as the world’s biggest motorcycle manufacturer. Rasmussen finally had access to a powerful engine for the DKW car (600 cc, 15 hp) in the form of the two-cylinder motorcycle unit (1927). The vehicle, which had a load-bearing body covered in imitation leather, had rear-wheel drive. It was produced in the Spandau district of Berlin from 1928.

An abbreviation for deluxe which is usually applied to a series of vehicles which is one step up from custom
Abbreviation for Data Link Connector (OBD)
Abbreviation for distributorless ignition
Abbreviation for Daylight opening, the area of the vehicle’s windows: windshield, backlight, and all side windows.
In Britain, a D shape bicycle lock called U-lock in North America
Abbreviation for dealer
Abbreviation for Drive Motor
Abbreviation for Drive Motor Control Module
Abbreviation for Drive Motor Coolant Temperature
  1. Abbreviation for digital motor electronics; a single control unit for both fuel injection and ignition control
  2. Abbreviation for Dimethyl Ether
Abbreviation for Direct Methanol Fuel Cell
DMPI Module
Abbreviation for Drive Motor Power Inverter Module
Digital Multimeter

Abbreviation for digital multimeter, an electronic device to display current, resistance, potential.

Abbreviation for Distributor Modulator System
Abbreviation for Department Of Motor Vehicles. The department in each state usually responsible for vehicle and driver licencing. The name differs between states.


A racing term for Did not finish.

A vehicle brand of which the 1925-1948 models are classic cars.
  1. Abbreviation for Double overhead camshaft
  2. Abbreviation for Diesel Oxidation Catalyst
  1. The floor or platform where trucks load and unload.
  2. A warehouse door with an extending platform where trailers are loaded and unloaded.


A formal record of a Federal Energy Regulatory Commission proceeding. These records are available for inspection and copying by the public. Each individual case proceeding is identified by an assigned number.
Dock Face
Outer wall of dock door.
Dock Leveler
A plate at the dock door entrance that raised and lowered either manually or hydraulically to accommodate trailer floor heights.
Dock Light
A light used to illuminate the inside of a trailer in order to aid in the loading and unloading processes.
Dock Plate
A moveable metal plate used as a ramp or bridge that is placed between the warehouse dock door and a trailer or railcar and makes it easier/smoother to access a trailer or railcar with a forklift or similar equipment.
Doctor test
A qualitative method of detecting undesirable sulfur compounds (i.e., H2S) in petroleum distillates, that is, of determining whether oil is Sour or Sweet.
Repair orders or other means used to record work performed on a vehicle.
Abbreviation for the U.S. Department of Defense
DodgeClick image for books on

A vehicle brand of which the 1967-70 Coronet R/T models are milestone cars. Models include the following:

  • 100 Pickup (19__-89), 150 Pickup (19__-93)
  • 250 Pickup (19__-93)
  • 350 Pickup (19__-93)
  • 600 (1984-88)
  • Aries America (1981-89)
  • Avenger (1995-2008)
  • Caliber (2007-08)
  • Caravan (1984-2007)
  • Colt (1970-94)
  • Colt Vista (1983-91)
  • Dakota (1987-2008)
  • Avenger (2007-present)
  • Caliber (2007-present)
  • Caravan (1984-2007)
  • Challenger (2008-present)
  • Charger (2006-present)
  • Dakota (1987-present)
  • Daytona (1984-93)
  • Diplomat (1977-89)
  • Durango (1998-present)
  • Dynasty (1988-93)
  • Grand Caravan (1987-present)
  • Intrepid (1993-2004)
  • Journey (2009-present)
  • Lancer (1955-59, 61-62, 85-89)
  • Magnum (2005-2008)
  • Mini Ram Van (19-__-88)
  • Monaco (1990-92)
  • Neon (1995-2006)
  • Nitro (2007-present)
  • Omni America (1978-90)
  • Raider (1987-89)
  • Ram (1981-present)
  • Ram 50 Pickup (19__-93)
  • Ram 1500 Pickup (1994-2008)
  • Ram 2500 Pickup (1994-2008)
  • Ram 3500 Pickup (1994-2008)
  • Ramcharger (1974-93)
  • Ram Van (1971-2003)
  • Ram Wagon (19__-2002)
  • Shadow (1987-94)
  • Spirit (1989-1995)
  • Sprinter (2003-present)
  • Stealth (1991-96)
  • Stratus (1995-2006)
  • Viper (1992-present)
Abbreviation for U.S. Department of Energy — the agency responsible for regulating energy sources including gas
  1. Man’s best friend.
  2. A vehicle in very bad shape, which may not be man’s best friend.
  3. A lug or protrusion on an object.
  4. A knob on the side of a gear that aligns or interlocks with a matching dog or hole in an adjacent gear.
  5. A small bent metal fitting used in closing doors, hatch covers, manhole covers, etc.; a bent bar of round iron used in holding shapes on bending slab; any small flat lug temporarily welded to structure as backing for a wedge.


Dog clutch
  1. A simple coupling with two halves called dogs, with square projections in one that engage in square slots in the other to transmit drive, but can also be disengaged to break the drive.
  2. Mating collars, flanges, or lugs which can be moved as desired to engage or disengage similar collars, flanges, or lugs in order to transmit rotary motion
Dog guard
A grid made of tubular bars or wire mesh to keep a dog in the back part of a vehicle
  1. An angled bend, often at the trailing edge of a window; also where the rear door curves around the rear wheelhouse of a four-door body style.
  2. The angle created at the door opening by the wrap-around windshields found on many mid to late ’50’s models.
Dogleg pillar
The C-post or C-pillar.
Dogleg section
An irregular shaped part of the leading edge of the rear quarter panel of a four-door sedan along the wheel cutout and up to the waistline
Dog Point
A cylindrical extension, or pilot, of diameter smaller than the minor diameter of the thread, commonly equal to about D/2 in length, with a conical section between it and the thread; usually used as a pilot in assembling or as the end of a set screw projecting into a fairly deep hole or slot.



  1. Abbreviation for double-overhead camshaft. Refers to an engine with two overhead camshafts.
  2. Abbreviation for Dual Overhead Cam
Do it to it
Trucker slang for Speed up as in ‘Now that we’re on the boulevard lets do it to it.’
Do-it-yourself market
(DIY) The vehicle maintenance and repairs conducted by the vehicle owner or friend/relative who purchase auto parts from a retail outlet.
Do-it-yourself mechanic
A person, whether qualified or not, who does his own repairs on his own vehicle.
Abbreviation for Data Output Line to IPC
  1. A metalworking tool, available in a variety of shapes and sizes, comprising a curved polished block of cast iron or forged steel, used to assist in forming three-dimensional shapes and in straightening dented panels, usually by holding the dolly behind the metal to be shaped and hammering the metal.
  2. A small two-wheeled non-motorized trolley or hand trukck for moving heavy objects.
  3. A trolley that supports the front wheels or back wheels of a disabled vehicle for towing it.
  4. A single-axle piece of trailing equipment used to hook two trailers together.
  5. A Converter dolly
Dolly Bar
A heavy bar to hold against a rivet, to give backing when riveting.
Groups of atoms that have same magnetic polarity
Dome Car
a two-level railway car that has a glass ceiling.
Sealed metal container for the motor compressor of a refrigerating unit.
Dome lamp
A dome-shaped interior light. Also called a dome light.
Dome light
A dome-shaped interior light. Also called a dome light.
A vehicle produced in Canada, United States, or Mexico. The opposite is foreign.
Domestic Fuel
As defined by the Energy Policy Act, Section 301, domestic fuel is derived from resources within the United States, its possessions and commonwealths, and Canada and Mexico (the two nations in a free-trade agreement with the U.S.).
Domestic vehicle producer
An original vehicle manufacturer that assembles vehicles in North America (U.S.A., Canada, or Mexico) for domestic use.
Donor car
A car from which parts are used to repair another one of the same type or to build a special or kit car
Do not enter

Do not enterDo not enter

A sign indicating that travel is not permitted down a certain road or in that direction

The hinged side panels of a vehicle which permit the occupants to enter or leave the passenger compartment. In most cases the doors open so that the hinge is toward the front of the vehicle. When the hinge is toward the back of the vehicle, they are called Suicide doors.

Door alignment
Accuracy or fitting of the door in the door aperture
Door aperture
Opening into which the door fits
Door beam
A longitudinal reinforcing bar which fits between the inner and outer shell of the door. It is designed to withstand side impacts. Also called a side impact bar.
Door bottom
The lower door area, both of the door skin and of the door frame, also the narrow horizontal lower panel of the door frame that has the drain holes
Door capping
The molding between the door trim panel and the window glass
Door check arm
A metal part near the hinge which has several notches which allows the door to remain partially or fully open
Door check strap
A leather strap near the hinge which prevents the door from opening too far.
Door face
The edges of a door which are not visible from the outside or inside when the door is shut. Also called door shut.
Door frame
  1. The bare skeleton of the door to which the door skin and door trim are added.
  2. The door aperture.
Door gap
The distance around the door between the edge of the door and the aperture
Door garnish molding
A trim molding located on the door panel along the edge of the window opening.
Door glass
The glass pane filling the top half of a door, which can usually be lowered or raised
Door handle
The interior or exterior handle for opening a door.

Door hinge
The pivoting part which is attached to the door frame and the door pillar. It allows the door to swing open or shut.
Door hold-open spring
A spring attached to the door hinge to provide a spring load to keep the door in an open position
Door latch
That part of the door lock which contacts the striker plate as the door is closed, and springs back when the door is fully shut to hold it in the closed position
Door lock
A mechanism for allowing a door to be opened either by the operation of a key on the outside of the door or by releasing a mechanical switch on the inside of the door.
Door lock de-icer
A fluid which is inserted into the key-hole to melt the ice which has bound the tumblers in a door lock.
Door mirror
An exterior, door mounted, rear-view mirror. On trucks and older vehicles the mirror is manually adjusted; but on many cars they are adjusted either by a cable inside the cab or by an electric motor with the switch inside the cab. The control device is located on the door, on the instrument panel, or on the console between the driver and passenger.
Door pad
The door inner trim panel
Door panel
A panel covered in vinyl or other material and mounted to the inside of the door
Door pillar
One of the vertical members of the body shell ahead of and behind the doors, which also support the roof structure and reinforce the body as a whole
Door pillar switch
A small switch, typically in the lower portion of the A-pillar, whose main function is to turn on the courtesy lights when the door is opened and to indicate that the door is open especially if the key is left in the door.
Door pocket
A container or pouch located on the lower inside portion of the door. It can be used to store maps and other small items
Door post
One of the vertical members of the body shell ahead of and behind the doors, which also support the roof structure and reinforce the body as a whole
Door protector
A strip of rubber, plastic, or chrome which fits over the edge of the door to protect it from damage when opened carelessly
Door pull
A handle on the inside of a vehicle door which allows the driver/passenger to pull his door shut
Door rates
The hourly rates charged by dealers on standardized units of service work. Hourly rates may or may not correspond to an actual hour of work.
Door seal
A weatherstrip surrounding the door to form a seal when the door is closed
Door shut
The edges of a door which are not visible from the outside or inside when the door is shut. Also called door face.
Door sill
The bottom part of the door frame (i.e., the pat under the door when it is closed).
Door skin
The large sheet metal panel of the door visible from the outside. Available to body shops as a replacement panel for most cars
Door speaker
Radio/stereo speakers mounted in the door panel
Door stay
A device incorporated in door hinges that keeps the door in an open position and prevents it from closing under its own weight
Door step
Top part of the outer sill, visible when the door is opened
Door surround
The faces of the door step, door pillars, and roof section which makes up the door aperture
Door trim
A panel covered in vinyl or other material and mounted to the inside of the door
Door trim pad
The covering used to conceal the lower portion of the inside panel of the door.
Door well
A cavity enclosed by the door frame, door skin, and trim panel containing the window winding mechanism and into which the window glass is lowered


Highly combustible alcohol/methanol-based fuel mixture
A vehicle brand of which the 1925-1948 models are classic cars.
Back to back seating on older cars where the driver and front passenger faced forward; but the two rear passengers faced rearward.
  1. Abbreviation for the U.S. Department of Transportation — an American federal agency
  2. Abbreviation of Department of Transport — a British agency

The department in each state usually responsible for the state’s road network. The name differs between states.

This brake fluid has a glycol base. It is clear or light amber in color. Its Dry boiling point is 205°C minimum and Wet boiling point of 140°C minimum. It will absorb 1 to 2 percent of water per year depending on climate and operating conditions. It is used in most domestic cars and light trucks in normal driving. It does not require cleaning the system and it can be mixed with DOT 4 and DOT 5.1 without damage to the system. The problem with it is that it absorbs moisture out of the air and thereby reduces its Boiling point. It can also damage the paint on a vehicle.
This brake fluid has a borate ester base. It is clear or light amber in color. Its Dry boiling point is 230°C minimum and Wet boiling point of 155°C minimum. It is used in many European cars; also for vehicles in high-altitude, towing, or high-speed braking situations, or ABS systems. It does not require cleaning the system and it can be mixed with DOT 3 without damage to the system. The problem with it is that it absorbs moisture out of the air and thereby reduces its Boiling point. It can also damage the paint on a vehicle.
This brake fluid generally has a silicone base. It is violet in color. Its Dry boiling point is 260°C minimum and has no Wet boiling point in federal DOT 5 Specifications. It is used in heavy brake applications, and good for weekend, antique, or collector cars that sit for long periods and are never driven far. It does not mix with DOT 3, DOT 4, or DOT 5.1. It will not absorb water and will not damage the paint on a vehicle. It is also compatible with most rubber formulations. The problem with it is that it may easily get air bubbles into the system which are nearly impossible to remove, giving poor pedal feel. It is unsuitable for racing due to compressibility under high temperatures. If as little as one drop of water enters the fluid, severe localized corrosion, freezing, or Gassing may occur. This can happen because water is heavier and not mixable with silicone fluids. It is unsuitable for ABS.
DOT 5.1
This brake fluid has a borate ester base. It is clear or light amber in color. Its Dry boiling point is 260°C minimum and Wet boiling point of 180°C minimum. It is used in severe-duty vehicles such as fleets and delivery trucks; towing vehicles, and race cars. It can be mixed with DOT 3 or DOT 4 without damage to the system. It maintains higher Boiling point than DOT 3 or DOT 4 fluids due to its higher borate ester content. It is excellent for severe duty applications. The problem with it is that it costs more than other fluids and there is limited availability. It also absorbs moisture out of the air and thereby reduces its Boiling point. It can also damage the paint on a vehicle.
DOT number
The symbol DOT on a tire means it meets or exceeds Department of Transportation safety standards. Following DOT are a maximum of eleven numbers. E.g., DOT FT TW A2NX 092. (DOT = meets or exceeds federal standards; FT = identifies manufacturing plant; TW = the code for tire size; A2N or A2NX-3 or optional four digits = manufacturer’s code to identify the characteristics of the tire; 092 = Week of mfg., in this case, 9th week of 1972. Prior to May 22, 1971 the manufacturer’s plant was identified by only three numbers (Example DOT 129). Retreaded tires must also have a new serial number and can be determined by the letter R following DOT letters.
A combination of a tractor and two semitrailers connected in tandem by a converter dolly. Also called Twins or Twin Trailers

Double A-arm suspension

Double A-arm suspensionDouble A-arm suspension

A suspension system which has two triangular (A-shaped) control arms as the main support of the wheel. The wide ends of both upper and lower A-arms are hinged to the frame. The narrow ends are attached to the upper and lower ball joints. The steering knuckle (including the stub axle or spindle that carries the wheel bearing and the wheel) is fixed between these ball joints. This configuration allows the wheel to move up and down with variations in the road surface and left and right as it is steered, while keeping the wheel in the correct position with respect to the road and the vehicle. A spring and a shock absorber are set between the frame and the lower A-arm (shown in image), or between the frame and the upper A-arm, to absorb road shock and to help control wheel movements.

(of a shock absorber or pump) having a piston with fluid on both sides so that in a pump one piston end performs the suction stroke while the other discharges the liquid, and in a shock absorber both upward and downward movements are damped
Double anchor drum brake
Double-barrel carburetor
Two throttle openings or barrels from the carburetor to the intake manifold. Also called twin-choke carburetor.

Double Bottom
  1. Colloquial term for a combination vehicle consisting of a tractor pulling a semitrailer and a full trailer.
  2. Compartments at the bottom of a ship between inner bottom and the shell plating, used for fresh water, ballast water, fuel oil, etc.
Double bus
A colloquial term for an articulated bus
Double Cab
Toyota’s term for a Crew cab
Double cap nut
(Budd mounting) A type of securing device which consists of an inner cap nut (sleeve nut) and an outer cap nut. It is the most common method for mounting disc wheels in dual.
Double century
A bicycle ride of 200 miles (321.9 km).
Double clutch
Double clutching
Vehicles with manual transmission and no Synchromesh have difficulty shifting from one gear to another. With synchromesh, shifting is accomplished by depressing the Clutch pedal and moving the Gearshift selector from one gear to the next. Without synchromesh, shifting is not smooth unless you double clutch. Here you depress the Clutch pedal shift to neutral lift up on the Clutch pedal blip the throttle (accelerator), then depress the Clutch pedal again and shift to the next gear. While this action seems complicated, you can get used to doing it to avoid the grinding noise heard in non-synchromesh transmissions.
Double coat
Two single coats of primer or paint applied with little or no flash time between them.

Double-cradle frame
A motorcycle frame with two steel tubes circling the engine from the front and cradling it
A passenger bus with a set of seats on a floor above a lower set.
Double-decker bus
A passenger bus with a set of seats on a floor above a lower set.
A British term for Double clutch
Double-Deep Storage Lane
Method of storing product in a warehouse two loads deep in an aisle.
Double Drop Deck
A trailer, usually a flatbed, with a floor set at three different heights, it steps down towards the middle and then steps back up at the rear. Sometimes referred to as a step deck.
Double duty case
Commercial refrigerator in which a part of space is for refrigerated storage and part is equipped with glass windows for display purposes.
Double-ended spanner
British term for Double-ended wrench
Double-ended wrench
A tool which has a hexagon ring at each end.
Double End Stud
Threaded at both ends with standard Class 2A threads to take nut assembly.
Double-Face Pallet
A pallet with both top and bottom deck boards that extend beyond the edge of the stringer and stringer board.
Double filament bulb
A light bulb with two filaments. For example a headlamp bulb with one for the high beam and another for the low beam; or a bulb with one filament for the stop light and another for the taillight.
Double flare
  1. The end of the tubing, especially brake tubing, has a Flare made so that the flare area uses two wall thicknesses. This makes a much stronger and safer Joint in bicycle tubing.
  2. A flare used on the ends of brake lines for extra strength. The tubing flared end is doubled over.
Double harley
Trucker slang for Putting the CB on channel 11 as in ‘Anyone looking to buy a good C.B. take it to the double harley.’
Double helical gear
A gear with two rows of inclined teeth, each forming an open V or chevron. Also called herringbone gear
Double hexagon socket
A socket with 12 points rather than the normal 6 points.
Double-leading brake
A non-servo brake in which both shoes are energized.
Double leading brake shoe
A system of braking where two hydraulic plungers and separate pivots create better braking when the vehicle is going forward; however it is not very effective when the vehicle goes in reverse.

Double-leading drum brakes
A drum brake having two leading shoes and no trailing shoes. Each shoe has its own activating cam and pivot.
Double nickel
Trucker slang for Traveling at 55 MPH as in ‘I sure got tired of running the double nickle.’
Double overhead cam
Double Overhead CamClick to supersize
Double Overhead Cam

(DOHC) An engine with two camshafts located above the cylinders. One drives the intake valves and the other operates the exhaust valve. In a single overhead cam engine (SOHC), one cam has enough lobes to drive both the intake and exhaust valves. The DOHC engine is considered to be a very sophisticated and more efficient engine; but is sometimes more difficult to adjust the valves. Also called twin overhead camshaft.

Double overhead camshaft
Double piston caliper
A hydraulic brake caliper with two pistons and provisions for applying hydraulic pressure equally to both pistons.
Double-Pitch Roller Chain
A roller chain having double the pitch of a standard roller chain, but otherwise having standard pins and bushings and standard or over-size rollers.
Double-pivot steering
Steering in which the steered wheels are pivoted on kingpins, which is the usual arrangement on motor vehicles.

Double reduction axle
A drive axle construction in which two sets of reduction gears are used for extreme reduction of gear ratio
Double reduction gearing
Gearing in which the ratio is reduced in two stages, used especially in heavy trucks
Double roller chain
Double-row chain
A chain having two rows of rollers. Also called Duplex. Double-row chains are used for primary drives.
Combination of a tractor and two semitrailers connected in tandem by a Converter dolly. Also called Twins or Twin Trailers. Also see

Doubles A-Train
Colloquial term for a truck tractor pulling more than one trailer connected by A-dollies.


Doubles B-Train
Colloquial term for a truck tractor pulling two semi-trailers where the second trailer sits on a fifth wheel that is permanently attached and extends off the rear of the lead trailer. Most commonly used on flatbeds or tank trailers. The B-train is considered a more stable double trailers configuration. B-dollies.


Doubles C-Train
Colloquial term for a truck tractor pulling more than one trailer connected by C-dollies. C-dollies.


Double shear strength
The resistance to breaking when a load is applied against an object in two places until the object breaks into three pieces.

Double thickness flare
Copper, aluminum, or steel tubing end which has been formed into two-wall thickness, 37 to 45 deg. bell mouth or flare.
Double-throw switch single-pole
(SPDT) Electric switch with one blade and two contact points.
Double-trailing brake
A non-servo brake in which neither shoe is energized.
Double-tube shock absorber
An older design of hydraulic shock absorber using two concentric tubes, one serving as the working cylinder, the other as the reservoir.

Double units
A set of twin 28-foot trailers, connected with a converter dolly, used to transport less-than-truckload (LTL) freight.
Double wishbone
A form of independent suspension used on the front of a vehicle where both the upper and lower wishbones are of equal length.
Double wishbone suspension
A form of independent suspension used on the front of a vehicle where both the upper and lower wishbones are of equal length.
Doubling Plate
A plate fitted outside or inside of another to give extra strength or stiffness.
Doughnut coupling
A flexible joint made of rubber and shaped like a ring doughnut. It is used, for example, between the front of the propeller shaft and the gearbox. Also called doughnut joint.

Doughnut joint
A flexible coupling made of rubber and shaped like a ring doughnut. It is used, for example, between the front of the propeller shaft and the gearbox. Also called doughnut coupling.
A pin projecting from one of two mating surfaces which fits into a corresponding hole in the other thus lining up the two pieces accurately during assembly. Also called Locating dowel
Dowel-bar retrofit
An innovation technique. Metal dowel bars inserted across adjacent concrete slabs joints in the pavement. The dowel bars distribute the weight of traffic across each joint evenly and keep the joints from moving up and down, which reduces damage to the roadway.
Dowel pin

Dowel pinDowel pin

  1. A small cylinder (steel or wood) which is passed through or partly through two parts to provide proper Alignment and to prevent movement between them. Sometimes called locating pin.
  2. Accurately dimensioned pin pressed into one assembly part and slipped into another assembly part to insure accurate alignment.
Dowel Screw
A fastener where both ends have gimlet points and is threaded similar to a lag bolt. The center section has a plain unthreaded shoulder. Used in joining two wooden members such as a leg to a table top.
Downdraft carburetor
A carburetor in which the air passes downward through the carburetor into the intake manifold. Contrasts with Sidedraft carburetor.
Downdraught carburetor
British spelling for Downdraft carburetor
Downflow radiator
A traditional type of vertical radiator, with header tank and bottom tank and a system of small tubes and cooling fins in-between, the hot water entering at the top and exiting at the bottom. This type of radiator has been replaced by a crossflow radiator.
A vertical force directed downward, produced by airflow around an object such as the body of a vehicle.
Downhand welding
Downhill bike
A bicycle designed for racing down mountains, features include long Travel (6 inches or more), dual suspension frame, great brakes, single chainring, long saddle, and a riser handlebar
The pipe that joins the entire exhaust system to the exhaust manifold.
The act of selecting a lower gear. In Britain it is called downward change.

  1. Manually shifting to a lower gear in order to use the engine compression to assist in reducing the vehicle’s speed especially when going down a steep hill. Also called downgearing.
  2. Manually shifting to a lower gear in order to increase speed for overtaking another vehicle. Also called shifting to passing gear.
  1. The downward movement of the piston, either the intake stroke or the power stroke in a four-cycle engine.
  2. Trucker slang for A hill going down as in ‘You can put her in georgia overdrive on the downstroke.’
Down Tester
Downtime occurs when a vehicle is being repaired (esp. a commercial vehicle), it cannot fulfil its function. There is a loss in both potential proceeds from its use as well as the salary of its operators.
Down tube
The bicycle frame tube running from the Headset to the bottom bracket one part of the main triangle on a bicycle frame.
Down tube shifter

Down tube shifterDown tube shifter

One of the gear shift levers mounted to the Down tube of a bicycle frame.

Downward change
A British expression of shifting the transmission to a lower gear. The North American term is Downshift.
  1. A portable frame straightening machine
  2. A blade used to move material by pushing. The vehicle itself is often called a dozer, and it may be tracked or wheeled.
  1. Abbreviation for Dash-pot
  2. Abbreviation for Drip-proof enclosure
Abbreviation for Dynamic Pressure Control
Abbreviation for Diesel Particulate Filter
Abbreviation for Differential Pressure Feedback EGR transducer measures the EGR gas flow into the inlet system
Abbreviation for Fuel Plug Inhibit
The fourth vertical post in a van or station wagon. Also called D-post
Abbreviation for Diesel Particulate Matter
The fourth vertical pillar in a van or station wagon. Also called D-pillar
Abbreviation for differential pressure regulator — an electro-magnetic operated pressure regulator. It gets a signal from the (ECU) requesting a richer or leaner fuel mixture
  1. Abbreviation for Door.
  2. Abbreviation for delivery receipt
  1. An unpleasant current of air intruding into the interior of a car.
  2. The depth of the ship below the waterline measured vertically to the lowest part of the hull.
  3. To follow behind a faster vehicle to take advantage of its air currents.
Draft Carburetor
Draft gauge
Instrument used to measure air movement by measuring air pressure differences.
Draft indicator
Instrument used to indicate or measure chimney draft or combustion gas movement. Draft is measured in units of .1 in. of water column.
The action of following closely behind a faster vehicle so as to take advantage of the aerodynamic effect which causes both the vehicles behind and the one in front to move faster.

Draft marks
The numbers which are placed on each side of a ship at the bow and stern from the lower edge of the number to the bottom of the keel
Draft regulator
Device which maintains a desired draft in a combustion-heated appliance by automatically controlling the chimney draft to the desired value.
  1. To accelerate a vehicle from a standing start, over a course one-fourth mile in length. Also called drag racing.
  2. Used by some drivers when referring to challenging another driver to an acceleration race.
  3. air resistance.
  4. The condition of a clutch when it fails to fully disengage. The plates still rub against each other and causes intermittent contact between the engine output and the transmission gears. Called clutch drag.
  5. The condition of brakes when the pads or shoes still rub the disc or drum. Called brake drag.
  6. The amount the stern end of the keel is below the bow end when the ship is afloat, but not on an even keel.
Drag coefficient
(Cd) A number used in calculating the aerodynamic drag acting on a vehicle. The drag coefficient is a function of factors like the shape of the vehicle, airflow through the vehicle for ventilation and cooling. The number is determined in a wind-tunnel or by coasting tests performed on the vehicle. The lower the drag coefficient the less drag on the vehicle and the more aerodynamic is the vehicle. A sleek vehicle has a drag coefficient, or Cd, of about 0.30; a square, flat plate’s is 1.98. Also signified by Cx. If D is the drag of a body in a uniform stream of density p and velocity V, the drag coefficient is Cd=2D/pV²S where S is a representative area of the body, usually taken as frontal area. A teardrop has a Cd of 0.05, a barn door about 1.15, a Toyota Previa minivan is 0.33, a Porsche about 0.30, the GM Impact 0.19, the GM Sunraycer 0.12.
Drag link
A steel rod connecting the pitman arm to one of the steering knuckles. On some installations the drag link connects the pitman arm to a center idler arm.
Dragon fly
Trucker slang for a truck with no power as in ‘Drag ‘er up one side of the hill, let ‘er fly down the other.’
Dragon wagon
Trucker slang for Tow truck as in ‘Looks like that bulldog is gonna need a dragon wagon.’
Drag plates
Metal plates that have a car club’s name and logo identifying the vehicle and its driver as a member of that club.
Drag race
A competitive match between two vehicles in which they race over a 1/4 mile course.
A specially constructed lightweight drag racing vehicle for drag racing, typically with a huge supercharged V-8 engine mounted well back in the chassis and extremely wide rear tires. Typical races are an acceleration contest from a standing start between two vehicles side by side over a measured distance. The accepted standard for that distance is either a quarter-mile (1,320 feet / 402.3 m) or an eighth-mile (660 feet / 201 m). A drag racing event is a series of such two-vehicle, tournament-style eliminations. During drag racing events, vehicles are classified by various criteria that take into account the extent of modifications to the car. These criteria include engine capacity, configuration of cylinders, frame type, vehicle construction materials, wheelbase, horsepower to weight ratio, number of cylinders, whether or not power adding devices such as turbochargers, superchargers or nitrous oxide are employed, vehicle type (such as car, truck, etc,), or even make and model for limited entry fields. The aforementioned divisions are in place to ensure that the cars are evenly matched during the race.
A quarter-mile stretch of track for drag racing
Drag wheel
Special steering wheel used on some Dragsters. Often consists of a crossbar spoke and a portion of rim on each end.
  1. To empty a container usually from the bottom.
  2. A tube or channel which allows water to run to another place.
A petcock or drain tap.

Drain hole
A hole drilled in the bottom of a box section or a door, to allow water that has accumulated to escape so as to prevent or delay rusting
Draining tray
A container used to catch oil when draining the sump, transmission, etc.
Drain plug
Usually a threaded plug at the lowest point of the sump, gearbox, cooling system, etc., which is removed in order to drain the oil or coolant, and typically has a recessed hexagon head.

Drain plug key
A tool for removing and tightening drain plugs, e.g., on transmissions and engine sumps, either as a multi-purpose tool with a number of different drives in the form of hexagonal or square projections at either end for different drain plugs, or as a special tool for one specific size of drain plug. Also called a drain plug wrench.
Drain plug spanner
A British term for a drain plug wrench
Drain plug wrench
A tool for removing and tightening drain plugs, e.g., on transmissions and engine sumps, either as a multi-purpose tool with a number of different drives in the form of hexagonal or square projections at either end for different drain plugs, or as a special tool for one specific size of drain plug. Also called a drain plug key.
Drain tap
A device which controls the flow of fluid (oil or coolant) out of the bottom of the cylinder block or the bottom of the radiator.
Drain valve
British spelling for Draft

Draught Carburetor
Draught excluder
A British term for weatherstrip
  1. To form wires by pulling the wire stock through a series of hardened dies.
  2. The process of removing the hardness from a piece of metal.
  3. The amount of electrical load or electrical requirement.
Refund of customs duties paid on material imported and later exported.

  1. Two converging bars forming a V-frame or an A-frame at the front of a trailer or motorhome, which carry the coupling for attaching to the towing vehicle
  2. A metal bar that connects a truck and trailer. Sometimes referred to as the tongue of the trailer.
Draw depth
The depth to which a stamping press can push or fold a metal sheet or panel.
Draw file
Smoothing a surface with a file moved sideward
Draw filing
A file is drawn across work at right angles.

Filing by passing the file, at right angles, up and down the length of the work.
The process of pulling material like a wire through a die to reduce its diameter to the size required.

A turbocharger system in which the turbocharger sucks the air/fuel mixture through the carburetor or fuel in, i.e., the air and fuel mixing occurs upstream from the turbocharger
A vehicle used to haul goods. A container or piggyback is moved from a rail yard to another location (which is most likely a Distribution Center) and then returning that piggyback or container back to the initial pick-up point, is known as a dray. It is important that these containers get unloaded quickly and returned back to the original point so not to incur detention charges.
The work or cost of hauling goods, i.e., transporting freight by truck, primarily in local cartage.
Abbreviation for demonstrated reserve base
Abbreviation for Diagnostic Readout Box (Chrysler)
Abbreviation for Distributor Retard Control Valve
Dream car
A one-of-a-kind futuristic, experimental automobile usually appearing at auto shows to stimulate interest in the manufacturer’s products. Much design benefit spurs from dream cars and many reach the production stage.
  1. To give (a rough surface, flanges, etc.) the right shape by grinding or a similar process.
  2. To prepare ore for smelting by removing impurities.
A motorcycle set up for long-distance touring
Insufficiently atomized fuel issuing from the fuel injection nozzle at or immediately following the end of the main injection phase
The slow loss of fuel from injection nozzle tip after cut-off
  1. A dehumidifier.
  2. A drying oven.
  3. Substance or device used to remove moisture from a refrigeration system.
  4. A device located in the liquid line, contains desiccant to absorb moisture from the system. Usually combined with the receiver
  1. A short bar or punch used with a hammer to drive a component in or out of place for removal or installation.
  2. The action where the rear end of a car swings to the right or left. In racing, a controlled drift will help you to go around the corner. In the winter, an uncontrolled drift might cause the car to face the wrong way or put you in the ditch.
  3. To deviate from the normal direction.
Drift Pin
A small tapered tool used in aligning holes in adjacent members.
Drift punch
A tapered tool which is hit with a hammer and used to remove or install pins, shafts, rivets, etc. or to align holes when inserting screws and bolts.
  1. A pointed cutting tool which is rotated under pressure to bore a round hole.
  2. The action of using a drill (usually a twist drill) to make a round hole.
Drill bit
A piece of rod with spiral recesses cut in it and a hardened steel tip, made in different sizes for drilling different sized holes, and inserted in the chuck of a drill
An expression used to describe a hole which has been cut into a crankshaft to allow oil to be fed to the main bearings on the connecting rod throws.
Drilled Head
Used in AN Bolts and machine screws, etc.
Drilled Shank
Used in AN Bolts and machine screws, etc.
Drill press

Drill pressDrill press

A nonportable machine used for drilling.

D ring


A D-shaped ring found on many models of bicycle shift levers, used to adjust the level of tension on the inner parts of the lever.
Drip molding
  1. The curved metal molding around the edge of the roof that directs water away from the side windows. Also called Drip rail
  2. The molding-like, U-shaped trough or gutter at the lower edge of the roof that catches rainwater and carries it away from the windows and doors.
Drip moulding
British term for Drip rail
Drip pan
Pan-shaped panel or trough used to collect condensate from evaporator.
Drip-proof enclosure
(DP) An electric motor housing with ventilation openings in the end shells and the shells placed so drops of liquid falling within an angle of 15° from vertical will not affect performance. Usually used indoors, in fairly clean, dry locations.

Drip rail
A gutter running along either side of the roof to take water to the front or rear of the car, and prevent it from dripping into the car when the door is opened. The British term is drip moulding
  1. To travel in a car as in the expression, ‘She drives to work.’
  2. To operate a vehicle as in the expression, ‘Martha can drive her Dad’s car.’
  3. To cause a wheel, shaft, etc. to turn or rotate.
  4. To propel a vehicle.
  5. A journey in a car as in ‘The drive to Chicago was uneventful.’
  6. To go for a drive as in, ‘We went for a drive last Sunday.’
  7. A stretch of private road leading to a house (i.e., driveway).
  8. A means of transmitting power or motion as in ‘The drive is controlled by a servo switch.’
  9. A tool which has a square end (1/4 inch, 3/8 inch, or 1/2 inch) which fits into a recess in a corresponding socket for the installation or removal of nuts and bolts.
  10. A die position.
  11. One of the forward gears marked on the gear selector of an automatic transmission.
The condition of a vehicle which may have many mechanical and appearance problems, but it has an engine which runs and wheels that turn, etc. so that it can be operated and driven.
The general qualitative evaluation of a powertrain’s operating qualities, including idle smoothness, cold and hot starting, throttle response, power delivery, and tolerance for altitude changes.
Drive axle
Any axle that carries power from the engine to the wheels that propel a vehicle. Also called power axle.
Drive belt
  1. A flat belt which connects two or more pulleys so as to transmit motion from one pulley to the other.
  2. The belt that transfers the rotation of the engine by way of the crankshaft pulley to drive the various devices such as the alternator for electricity, water pump for the cooling system, air conditioning compressor for air conditioning, or power steering pump for ease of steering.
Drive cable
Drive chain
An endless chain which encircles two or more sprockets so as to transmit motion from one sprocket to the other
Drive Cycle
Any journey of a vehicle in which the engine temperature is raised from cold (below 49°C) to normal operating temperature (above 71°C)
Drive end
The end of an alternator, generator, etc., where the drive pulley or gear is located.
Drive end bracket
The cover which houses the drive end of an alternator or generator
Drive fit
A condition of fit (contact) between two parts that requires pressure to force the parts together. Usually the shaft is slightly larger than the hole so that they must be pounded or forced or driven together. Also called Force fit, Press fit, or Interference fit.
Drive gear
The gear which transmits the power to a driven gear.

Drive handle
A tool, typically in the form of a bar, for turning sockets to loosen and tighten nuts and bolts, with a male square drive to be inserted into the female square drive of sockets for the turning operation. They include ratchets, jointed handles, speed brace, T-handles, torque wrenches, speeder handle, and breaker bar.

Drive-in Rack
Storage racking equipment that has side rails to enable warehouse operators to stack product high in deep rows. It provides access only from aisles.
Drive layout
The arrangement of the order of the engine, transmission, and driven axles, e.g., Front-wheel drive, rear-wheel drive, mid-engine drive, four-wheel drive, two-wheel drive
Drive line


  1. All the individual components beyond the engine up to the wheels (e.g., clutch, drive shaft, differential, driven axles); but not the engine or transmission. Also called drivetrain or powertrain
  2. All the components which together transmit power from the transmission to the drive axle(s). These consist of at least one driveshaft (propeller shaft) with a universal joint at each end.
Drive module
Interchangeable unit providing motive power, either in the form of an electric motor and ancillaries, or an internal combustion engine with all necessary components, for alternative use in the same vehicle according to needs and conditions
Drive motor
Electric motor providing motive power in an electric vehicle
Something made to rotate by the engine or some other source of motive power.

Driven axle
The axle to which power is transmitted to drive the vehicle
Driven gear
An engine needs to transmit power to the wheels by the use of sprockets and chain (as in a motorcycle) or by a drive gear which meshes with a driven gear to propel the vehicle.
Driven plate
  1. The central clutch plate carrying clutch linings and held under pressure between the flywheel and the pressure plate when the clutch pedal is released, and transmitting power to the gearbox input shaft via splines
Driven pulley
A pulley which is surrounded by a belt to receive power from the drive pulley
Driven sprocket
On a vehicle which uses a chain (like a bicycle and some motorcycles), there are two important sprockets the drive sprocket is connected to the power source (the engine or your pedals) and the driven sprocket is usually connected to your rear wheel.
Driven wheel
The wheel (or wheels) to which power is transmitted to drive the vehicle
Drive pinion

Drive pinionDrive pinion

The shaft that takes power from the clutch into the Gearbox.

Drive plate
  1. A light plate bolted to the crankshaft to which the torque converter is attached in a vehicle with automatic transmission.
  2. A clutch plate which is indexed into clutch basket (outer hub) by tabs. Drive plate has friction material bonded to its surface. When the clutch is engaged, the drive plate transfers power to the driven plate.
Drive powertrain
Drive pulley
  1. A pulley which is surrounded by a belt to transmit power to the driven pulley
  2. The pulley attached to the nose of the engine crankshaft. It drives the compressor clutch pulley, usually with a V-type drivebelt
  1. A collectible vehicle which is too good to treat as a beater and not quite good enough to show. It is a presentable old car or truck that is used for everyday purposes. It is maintained as though it were a late-model vehicle. With care, it could be easily restored to show car condition.
  2. A person who operates the controls of a vehicle to regulate its speed and direction.
  3. A switched electronic device housed in a computer that controls output state. For example, a driver controls how long a fuel injector remains open.
  4. A tool used to insert something like a fastening device (e.g., screwdriver).
Driver air bag
Original type of air bag, designed to protect the driver from being hurled into the steering wheel and instrument panel
Driver and Vehicle Licensing Agency
(DVLA) A section of the British Department of Transport which is responsible for keeping records of all registered vehicles and issuing registrations and licenses for vehicles as well as licenses for drivers. The center is located in Swansea.
Driver and Vehicle Licensing Center
The location for the British Driver and Vehicle Licensing Agency located in Swansea.
Drive ratio
Driver Collect
A shipment for which the driver must collect freight charges at the time of delivery.
Driver error
A mistake made by the operator of a vehicle particularly when there is an accident. An accident may be caused by a vehicle failure (e.g., a tire blowout), unsafe road conditions (e.g., snow, ice, fallen rock or tree), the inattention of a pedestrian, or the fault of a driver (e.g., drunkenness, inattention, intentional damage, disobedience to rules of the road).
Driver evaluation
A test of a driver’s ability to handle a vehicle. May be used to grant a driver’s license for a particular type of vehicle (i.e., motorcycle, passenger car, truck, bus, taxi)
Driver Head
A head, on a bolt or screw, designed for driving the fastener by means of a tool other than a wrench, such as a screwdriver.
Driver reaction distance
The distance traveled between the point at which the driver perceives a demand for braking and the start of brake application.
Driver reaction time
The time elapsed between the instant the driver perceives a demand for braking and the start of brake application
Colloquial term for drive axle tires.

Driver Team
A pair of drivers who alternative driving and resting.
Drive Screw
A piloted, multiple threaded screw with a large helix angle, used for permanent applications. It forms a mating thread as it is hammered or pressed into a prepared hole.

Drive Screw Nail
drive screw nail
Drive screw nail

A helically (continuous spiral) threaded pallet nail.

DriveshaftClick image to supersize

The shaft connecting the transmission Output shaft to the differentialPinion shaft. It transmits power from the transmission to the differential. It is found primarily on rear-drive vehicles. There is usually a Universal joint on either end. Also called propeller shaft.

Drive shaft
Driveshaft safety strap
A metal strap or straps, surrounding the driveshaft to prevent the shaft from falling to the ground in the event of a Universal joint or shaft failure.
Drive sprocket
On a vehicle which uses a chain (like a bicycle and some motorcycles), there are two important sprockets the drive sprocket is connected to the power source (the engine or your pedals) and the driven sprocket is usually connected to your rear wheel.

Drive Switch
Drive-Through Rack
Storage racking equipment with side rails to enable warehouse operators to stack product high in deep rows. Unlike Drive-in Rack, Drive-Through Rack allows access from either end of the row, as opposed to only being accessible from the aisle.
Drive tool
Any accessory for use with a socket wrench, including the drive handle
Drive train
  1. The entire moving part of the car or motorcycle: Engine, clutch, transmission, driveshaft, differential, axles, and sometimes the wheels.
  2. The moving parts of a bicycle: derailleurs, chain, freewheel, and crankset.
  1. The entire moving part of the car or motorcycle: Engine, clutch, transmission, driveshaft, differential, axles, and sometimes the wheels.
  2. The moving parts of a bicycle: derailleurs, chain, freewheel, and crankset.
Drive transaxle
  1. A short drive, often leading to a garage
  2. A privately maintained access to residential, commercial, or industrial properties.
Drive wheels
The set of wheels that actually propel the car forward and backward. Vehicles are now identified as having Front-wheel drive, Rear-wheel drive, Four-wheel drive, or All-wheel drive.
  1. Providing motive power, making a gear, shaft, etc. rotate.
  2. Controlling the movement and direction of a vehicle.
Driving axle
The axle which is driven by the engine through the drivetrain. Used to hold, align, and drive rear wheels and support weight of vehicle on rear wheel drive cars, or half shafts on front wheel drive cars that provide torque force to front wheels. Also called the drive axle or driven axle
Driving conditions
The situation created by the amount of traffic, the weather, and state of the roads
Driving gear
The gear which is driven by the engine. Also called the driven gear
Driving habits
The personal behavior of the driver when controlling the vehicle, including the speeds he travels, how and when he shifts gears, how he uses the brakes, when and if he uses his signal lights, how he changes lanes, how he turns corners, etc.
Driving lamp
A British term for driving light or spot light.

Driving license
A British term for driver’s license or operator’s license. A document which allows the holder to drive a certain type or types of vehicle, and is the only document required to be carried by the driver in Britain
Driving light
An auxiliary light used at night to illuminate the side of the road and increase the viewing distance.

Driving mirror
A British term for either the interior rear-view mirror or the mirrors mounted on the outside of the front doors or the front fenders
Driving position
The position in which the driver grasps the steering wheel and adjusts the location of the seat in relation to the pedals.
Driving style
The manner in which the driver handles a vehicle.

Driving wheel
The wheel(s) which is driven by the engine through the drivetrain. Also called the driven wheel
Abbreviation for Daytime Running Lights, a system that automatically turns on the vehicle’s low beam headlights (or in some cases, a low-power high beam headlight or even bright park lights) when the parking brake is released and the ignition is on.
A condition of a turning flywheel which can be controlled from no load to full load. Also called steady state speed regulation.
  1. A sudden reduction of pressure or voltage, etc.
  2. On a bicycle, the vertical distance from the horizontal line connecting the two wheel axles and the bottom bracket, one way of determining the location of the bottom bracket in relation to the rest of the Bicycle frame


  3. The action of leaving behind. For example in a race, you drop the vehicle you pass (i.e., overtake) and he gets further behind you as you continue to speed away.
  4. A location where your supplies have been cached. In randonneuring events of 1200 km, you can pre-arrange to have a bag of extra clothes and other supplies waiting for you at a prescribed control (i.e., checkpoint). Also called a bag drop.
Drop arm
A British term for the pitman arm
Drop Center
The main part or center of the frame is dropped down between the front and rear wheels to lower the vehicle to create a lower center of gravity.
Drop-center axle
A beam axle in which the main central portion of the beam is lower than the wheel centers, which was the usual layout for front axles until independent front suspension became almost universal
Drop-center rim
Drop center rim
A one-piece rim with a deep center section which is lower than the two outer edges, this allows the bead of the tire to be pushed into the low area on one side while the other side is pulled over and off the Flange. The British term is ‘well-base rim’
Drop center rim taper
A passenger rim where both bead seats are tapered 5° or a tubeless truck rim where both bead seats are tapered 15°.
Drop-centre rim
Drop centre rim
Drop Deck
Drop forged
A part that has been formed by heating the steel blank red hot and pounding it into shape with a powerful drop hammer.
Drop forged steel
A piece of steel shaped between dies while hot
Drop forging
  1. A piece of steel shaped between dies while hot
  2. Forming metal, usually under impact, by compression within dies designed to produce the required shape.
  1. A British term for a convertible. The word ‘head’ refers to the roof.
  2. Having a folding top which can be raised or lowered over the passenger compartment.
Drophead coupe
(DHC) This is a two-door automobile which has the appearance of a convertible, but the roof is fixed in place. In Europe, it is called a cabriolet.
Drophead coupé

  1. A convertible
  2. A two-door automobile which has the appearance of a convertible, but the roof is fixed in place.
  3. In Europe, it is called a cabriolet.
Drop-Off Charge
The fee made by a car rental company for a one-way rental.
One of two slots in the frame into which the rear wheel axle fits.


Dropout hanger
A threaded metal piece that extends below the right rear Dropout of a bicycle used as a mount for the rear derailleur.
Dropped axle
A front axle that has been altered so as to lower the frame of the vehicle, consists of bending the axle downward at the outer ends.
Dropped valve
A situation where the rising piston hits a valve which has become dislodged or open at the wrong time.
The lower, straight portion of a turned-down-type handlebar set.
Drop Strake
A strake discontinued near the bow or stern.
A colloquial term for convertible.
Drop Trailer
Druid forks
Side-sprung girder forks on a motorcycle. Druid was the original maker
  1. The part of a drum brake that rotates with the axle hub. The brake shoes press against the inside of the drum when the brakes are applied
  2. A cylindrical container.
  3. A Housing for transmission gears where the Bands are located.
  4. To make a whump, whump sound.
Drum brake
Drum BrakeClick image to supersize
Drum Brake

A type of brake using a shallow drum-shaped metal cylinder that attaches to the inner surface of the wheel and rotates with it. When you press down on the brake pedal, curved brake shoes with friction linings press against the inner circumference of the drum to slow or stop the vehicle.

Drum brakes
Drum compound
Drum lathe
Drum Parking Brake
Drum web
The metal plate or structure that fills the closed edge of the drum
  1. For paint, to lose its wetness often to the place where the surface is not even tacky.
  2. For bearings, to lack grease or other lubricant.
  3. Without oil
Dry ballast
A form of ballasting where a fine powder of barium sulfate is inserted inside the tire. It is sometimes referred to incorrectly as Lead ballast because of one brand name, Ledballast®.
Dry battery


Dry-blast cleaning
Method of cleaning parts using a dry medium, such as sand, glass beads, or crushed nut shells.
Dry boiling point
The temperature at which fresh brake fluid from a new container will boil.

Dry box
Trucker slang for freight trailer as in ‘I pulled both skateboards and dry boxes.’
Dry bulb
An instrument with a sensitive element to measure ambient air temperature.
Dry bulb temperature
Air temperature as indicated by an ordinary thermometer.
Dry bulk tanker
Sometimes called air-can trailers. Used exclusively for hauling dry bulk material. Cargo is emptied pneumatically.
Dry capacitor condenser
Electrical device made of dry metal and dry insulation; used to store electrons.
Dry cargo ship
Vessel which carries all dry cargo
Dry cell
A battery (like a flashlight battery) that uses no liquid electrolyte.
Dry cell battery
Electrical device used to provide DC electricity, having no liquid in the cells.
Dry charged battery
A battery with the plates charged but lacking electrolyte; when ready to be placed in service, the electrolyte is added.
Dry clutch
A clutch where the plate or plates do not run in a oil bath as opposed to a ‘wet clutch’ which does.
Dry dock
  1. An enclosed basin used to place a ship on dry land so that all the submerged parts and fittings can be repaired.
  2. A watertight vessel fitted with pumps and valves usually built in a U-shape. The valves are opened, the vessel sinks, the vessel to be docked is pulled over the drydock deck, the valves are closed and the pumps are started, as the drydock becomes more buoyant, drydocking the vessel to be repaired.


Dry friction
Dry friction exists when the rubbing parts have no other substance between them and are clean of other materials (i.e., no grease or oil). Opposite to Wet friction.
Dry galvanizing
A hot-dip galvanizing method in which the metal components are first immersed in a solution of flux and then dried, so that they become pre-coated with a thin film of flux, which melts in the zinc bath, to which certain metals, such as tin and aluminum, may be added to give fluidity, and in the case of tin, brightness. The opposite is Wet galvanizing
Dry gas
Dry hole
An exploratory or development well found to be incapable of producing either oil or gas in sufficient quantities to justify completion as an oil or gas well.


Dry ice
Refrigerating substance made of solid carbon dioxide which changes directly from a solid to a gas (sublimates). Its subliming temperature is -79°C.
Drying Adhesives
Drying agent


Drying oil
Any oil that hardens in the presence of air and sunlight
Drying oven
An enclosure where painted vehicle bodies are subjected to heat in order to dry and/or bake on the paint
Drying time
The time required for a solvent to evaporate after an adhesive film has been spread over the two surfaces to be bonded
Dry joint
A faulty electrical joint which does not give proper contact
Dry liner
When a cylinder sleeve is pressed into a bore and the cooling fluid does not contact the outside of the sleeve, the engine has a dry liner.


Dry manifold
An intake manifold with no integral coolant passages cast into it
Dry natural gas
Natural gas which remains after:

  1. the liquefiable hydrocarbon portion has been removed from the gas stream (i.e., gas after lease, field, and/or plant separation)
  2. any volumes of nonhydrocarbon gases have been removed where they occur in sufficient quantity to render the gas unmarketable.

Dry natural gas is also known as consumer-grade natural gas. The parameters for measurement are cubic feet at 15.5°C and 14.73 pounds per square inch absolute.

Dry setting
The adjustment of the float with a graduated rule or drill bit while the carburetor is disassembled on the bench. Usually consists of setting a prescribed clearance between the top of the float and the air horn
Dry sleeve
A cylinder sleeve application in which the sleeve is supported in the block metal over its entire length, the coolant does not touch the sleeve itself.

Dry spray


A paint fault where the paint pigment is not being held properly by the binder, or where the binder evaporates before the paint reaches the surface. Atomized paint that does not dissolve into the material being sprayed. It is caused by holding the gun too far from the work, too much air pressure or a Solvent that evaporates too fast.
Dry sump
A lubrication system in which the engine’s supply of oil is not contained in the crankcase (sump) but is pumped to the engine from an external container. This system allows the crankcase to be reduced in size and the engine to be installed lower in the chassis, and eliminates the oil starvation most conventional oiling systems suffer when subjected to the accelerative, braking, and cornering forces generated by a racing car.
Dry sump lubrication
Oil is gravity fed to the supply side of the oil pump from a remote oil tank. After the oil has been pumped through the four-stroke engine, it is returned to the oil tank by the return side of the oil pump.


Dry system
Refrigeration system which has the evaporator liquid refrigerant mainly in the atomized or droplet condition.
Dry type evaporator
Evaporator in which the refrigerant is in the liquid droplet form.
Dry weight
The weight of a vehicle without any fuel, oil, or coolant.

Abbreviation for Diesel Severe oil for use in under adverse conditions in diesel engines.
Abbreviation for demand-side management
Abbreviation for Digital Storage Oscilloscope
Abbreviation for Diagnostic Subroutine (Ford)
Abbreviation for Downshift Solenoid
Abbreviation for Dual Signal Spark Advance (Ford)
Abbreviation for deceleration solenoid valve
Abbreviation for Diagnostic Trouble Code
Abbreviation for Diagnostic Trouble Code Count Code
Abbreviation for Diagnostic Trouble Code Freeze Frame
Abbreviation for Diagnostic Test Mode
Cadillac DTS BooksClick image for books on
Cadillac DTS

A model of automobile manufactured by the Cadillac division of General Motors from 2006-current to replace the De Ville

Abbreviation for Dual Temperature Vacuum Switch
Abbreviation for dealer tank wagon
  1. A combination of two nearly identical parts (e.g., a truck with dual tires has two tires at each end of the axle).
  2. In Britain, dual is a verb meaning to Twin a highway or railroad.
Dual axles
Dual bead tire
Heavy service and large truck tires using two or more sets of bead wires in each bead rather than one.
Dual-bed catalytic converter
A catalytic converter which combines two converters (with different catalysts) in a single housing
Dual brake
Dual brakes
Dual brakes
Dual brakes
A brake system that uses a tandem or dual master cylinder to provide separate brake system for both front and rear of vehicle. In the event of a loss of hydraulic fluid, one system may still work because it is independent of the other system. Often the front left brake is linked with the right rear brake. Likewise the right front brake is linked with the left rear brake. Some cars like the Rolls-Royce, link the two front brakes with the right rear brake, and the two front brakes with the left rear brake. Also called dual-circuit braking system.

Dual brake system
A brake system that uses two hydraulic circuits. Should one circuit fail, the other remains operational
Dual braking system
Dual breaker points
A distributor, using two sets of breaker points, to increase the cam angle so that at high engine speeds, sufficient spark will be produced to fire the plugs.
Dual carbs
Two carburetors on the same engine allowing more fuel and air mixture to enter the engine.
Dual carburetors
Two carburetors on the same engine allowing more fuel and air mixture to enter the engine.
Dual carriageway
A British term for a divided highway (i.e., a road that has four lanes — two in one direction and two in the other — separated by a median).

Dual Catalytic converter
A Three-Way Catalyst (TWC). Also called a dual-bed converter
Dual-circuit braking system
A brake hydraulic system composed of two separate hydraulic circuits.

Dual controls
A second set of controls for use by a driving instructor when teaching someone to drive
Dual cowl
dual cowl Chrysler
1940 LeBaron Chrysler Newport Dual Cowl Phaeton

A touring car design, where the cab is divided into two compartments with a front and rear seat. It also has a second windshield mounted on a folding cowl to protect backseat occupants.

Dual-crown fork
A type of bicycle suspension fork that resembles a motorcycle fork due to crowns above and below the head tube, which increase stiffness
Dual drive
  1. Tandem axles, both powered directly by the engine.
  2. Colloquial term for twin screw.
Dual exhaust system
Dual fuel engine
An engine equipped to operate on two different fuels such as gasoline and LP-Gas
Dual-Fuel Vehicle
  1. EPACT Definition: A vehicle designed to operate on a combination of an alternative fuel and a conventional fuel. This includes:
    1. vehicles using a mixture of gasoline or diesel and an alternative fuel in one fuel tank, commonly called flexible-fueled vehicles
    2. vehicles capable of operating either on an alternative fuel, a conventional fuel or both, simultaneously using two fuel systems commonly called bi-fuel vehicles.
  2. CAA Definition: Vehicle with two separate fuel systems designed to run on either an alternative fuel or conventional gasoline, using only one fuel at a time.
Dual Ghia
A vehicle brand of which the 1956-58 models are milestone cars.
Dual ignition system
Dual-line braking system
A braking system in which a towing vehicle and trailer are connected by two or more brake lines
Dual master cylinder
Type of master cylinder associated with two compartments for displacing brake fluid under pressure in a split hydraulic brake system
Dual mounting
Two tires mounted together on each side of an axle of several types Cast spoke wheel, Disc wheel type (held on by Double cap nuts or Inner cap nuts and Outer cap nuts), Chevrolet type, and Motor wheel type
Dual overhead cam engine


Dual-piston engine
Dual-piston master cylinder
Dual-power brake system
A system that uses both a vacuum booster and a hydraulic booster to increase brake application.
Dual-purpose motorcycle
Street-legal motorcycles with varying degrees of off-road capabilities. Also called dual-sport
Dual purpose ship
Specially designed ship for carrying different types of cargoes such as ore and/or oil.
Dual-range gearbox
Dual-range transmission
  1. A transmission in a four-wheel drive vehicle and some motorcycles with two sets of ratios, usually a higher set for road use and a lower set for off-road use.
  2. An auxiliary transmission, also called a subtransmission, that is placed between the main transmission and the final drive system.
Dual-rate charging system
A charging system that switches extra coils into the charging system when the lights are turned on or there is an extra draw on the system.
Dual reduction axle
A drive axle construction with two sets of pinions and gears, either of which can be used
  1. Two sets of exhaust pipes and mufflers — one for each bank of cylinders.
  2. Two tires on each end of an axle.
Dual-servo drum brake
A type of self-energizing drum brake that has servo action in both forward and reverse
Dual spacing
A measurement in inches (or millimetres) from the center of the tread of one tire, to the center tread of the other tire in dual, which provides clearance between duals for air circulation.
Dual sport
Street-legal motorcycles with varying degrees of off-road capabilities. Also called dual-purpose motorcycles
Dual-suspension bike
A bicycle with front and rear suspension; also known as a dualie
Dual-tone horn
Dual Wheels
Four wheels per axle rather than two.
A 28-foot trailer designed to be pulled two or three at a time by one tractor. Also referred to as a ‘pup’ or ‘doubles.’


Dubonnet suspension
An independent front suspension and steering arrangement used in the 1930s and ’40s, in which the axle beam is rigidly attached to the vehicle frame, and the kingpins carry sprung steering and suspension arms, from which the wheels are mounted on stub axles
Click image for books on Ducati
A motorcycle manufacturer
A tube or channel through which air, gas, or liquid is conducted, conveyed, or moved.

Duct And Valve Vacuum Motor
Ducted fan
A fan mounted within a chamber or duct
Metal which can be bent, hammered, or drawn out into wire or sheet without fracturing
Ductile cast-iron
Iron that can be bent, hammered, or drawn out.
The ability of a material to undergo stretching or bending without fracturing
DuesenbergClick image for books on

A vehicle brand of which all models from 1921 are classic cars.

Expression to indicate quality, as It’s a duesy. The word is derived from the high quality Duesenberg automobiles.
Abbreviation for Driving Under The Influence of alcohol or drugs which is illegal everywhere.
  1. A paint finish that is not shiny.
  2. A blade, saw, or drill bit that is not sharp.


The front extensions of the side members of a chassis frame in older designs, to which were fitted the front ends of the leaf springs carrying the front axle.
A stuffed figure made to look like a human being, used, for instance, when crash testing cars. Also called a crash test dummy.

Dummy lights
  1. Exterior lights which do not work, but may enhance the appearance of a vehicle.
  2. The idiot lights that indicate a condition, but does not give details as a gauge would do, e.g., an oil light that indicates low pressure. By the time it comes on, you may have damaged your engine.
Dummy load
When testing an antenna or an electric circuit, a temporary resistance is placed in line to simulate what would be experienced when the unit is connected.
Dummy piston
A disk placed on the shaft of a reaction turbine.
A cargo body with a hydraulic, electric, or mechanical lifting mechanism that tilts to unload cargo. Includes side dumps, walking dumps, flatbed dumps, and dump trucks with snow plows or blades.

Dump body
A large truck’s metal body which is generally hinged at rear and dumped by hydraulic means. The size is generally given in cubic yard water level capacity.
A large metal container for garbage. The term is sometimes used to describe refuse trucks. Dumpsters are different from a roll-off containers. A dumpster is usually kept at a garbage collection point and not carried on a refuse truck. Some refuse trucks carry dumpsters short distances for loading, unloading, or distribution.
Dump trailer
A trailer unit that is able to unload its cargo in one of three ways: back dump (the front of the trailer is raised and the cargo slides out the back); side dump (the cargo bucket tilts to one side allowing the cargo to slide off); bottom dump (panels open under the cargo bucket to let the cargo fall beneath).
Dump truck
  1. A large truck with a bed designed to be tilted at its front to unload its contents usually through a gate in the rear.
  2. In Britain it is a small truck with a tipping container in front of the driver, used in construction, like a front-end loader
Dump valve
A valve for relieving pressure, such as that between the turbocharger and the carburetor in some systems
Cushioning material (e.g., cardboard, pallets, plywood, foam rubber, air bags) placed among cargo to prevent their motion or damage while in transit.
A drum brake that has servo action in both the forward and reverse directions.
Duo-servo brake
A servo brake with one double-end wheel cylinder and two linked self-energizing brake shoes
Duo-servo drum brake
A type of self-energizing drum brake that has servo action in both forward and reverse
Double, having two parts. Applies to motorcycle frames with two downtubes, and chains with double rows of rollers
Duplex chain
A chain with two rows of rollers, used especially for timing chains.

Duplex Roller Chain
Double strand chain (80-2) (Double Strand).
A vehicle brand of which models built between 1925-48 are classic cars.
  1. The ability of a component or entire vehicle to last a long time.
  2. The expected lifespan of a paint film
The ability of something to be serviceable for a long time before being replaced
Duraspark system
Ford electronic ignitions system
The length of time that an action (e.g., a valve) is allowed to operate or that something is supposed to last.

A device to indicate the hardness of rubber.
Dust boot
  1. A covering (often shaped like an accordion) usually made of rubber or plastic to cover over a shaft, CV joint, etc.
  2. A rubber diaphragm-like seal that fits over the end of a hydraulic component and around a pushrod or end of a piston, not used for sealing fluid in but keeping dust out
  3. Flexible rubber or plastic covers that seal out foreign matter from brake components
Dust cap
  1. A metal or plastic covering that fits into a hub shell to keep contaminants out of hub bearings.
  2. A metal or plastic end cover for a spindle in a pedal or a cotterless crankset.
Dust cover
  1. A soft, flexible valve cap to protect the valve assembly from dust while in shipment and storage. It is not capable of sealing the air pressure and should not be used in service.
  2. Small plugs made of rubber or metal, used to cover the access holes in backing plates and brake drums.
Dust-free paint
A condition of paint which has hardened beyond being tacky so that any air-borne dust particles will not be imbedded in the paint.
Dust sheet
A sheet for covering a car when in a garage and not in use.

Dust shield
Sheet metal disc or plate placed on the brake assembly to keep debris from brake assembly. Also called splash shield.
Dust spot efficiency
Dust Weight Arrestance
On a sedan or coupe, the sheetmetal surface or panel between the backlight (i.e., back window) and the top edge of the decklid.
Duty Case
Duty cycle
  1. (DC) The relationship between the operating and rest time. An electrical motor which can continue to operate within the temperature limits of its insulation system after it has reached normal operating (equilibrium) temperature is considered to have a continuous duty (CONT) rating. One which never reaches equilibrium temperature but is permitted to cool down between operations is operating under intermittent duty (INT) conditions
  2. Many solenoid-operated metering devices cycle on and off. The duty cycle is a measurement of the amount of time a device is energized, or turned on, expressed as a percentage of the complete on-off cycle of that device, in other words, the duty cycle is the ratio of the pulse width to the complete cycle width
  3. The percentage of time that a circuit is energized during one complete on/off cycle during pulse-width modulating.
Duty-cycle solenoid
The duty-cycle solenoid is a computer-controlled device in a feedback carburetor that alters the mixture adjustment. Also called a Mixture control solenoid
Duty drawback
Import duties or taxes repaid by a government in whole or in part, when the imported goods are re-exported or used in the manufacture of exported goods.
Duty paid value
In respect to imported goods, is the aggregate value for duty on imported goods.
Duty waiver
Forgiveness, in whole or in part, of import duties when certain conditions are met.
Abbreviation for Delay Valve
Abbreviation for Distributor Vacuum Advance Control Valve
Abbreviation for Delay vacuum bypass system
Abbreviation for Differential Vacuum Delay and Separator Valve
Abbreviation for Distributor Vacuum Delay Valve
Abbreviation for Driver and Vehicle Licensing Agency
Abbreviation for Driver and Vehicle Licensing Center
Abbreviation for Digital volt-ohm multimeter
Abbreviation for Relay Valve Two Way
Abbreviation for Distributor Vacuum Vent Valve
  1. In a contact breaker ignition system, the number of degrees the breaker cam rotates from the time the breaker points close until they open again. Also called the dwell angle or dwell period.
  2. In a breakerless ignition system, the time during which the electronic control unit allows current to flow through the primary winding of the coil, which in ignition systems with a Hall generator is determined by the width of the vanes.
  3. The length of time in crankshaft degrees the ignition contact points are closed.
Dwell angle


Dwell-angle control
A system which makes sure that the dwell is sufficient for all engine conditions
Dwell-angle map
The pattern described by the electronic dwell-angle control, dependent on engine speed and battery voltage
Dwell meter
An instrument which determines the number of degrees the breaker cam rotates while the breaker points are closed. Changing the Point gap affects the dwell angle. When the breaker points are correctly gapped, the distributor can give the proper amount and Duration of spark to the spark plugs.
Dwell period
The time during which the primary circuit is closed and primary current flows through the ignition coil, given in crankshaft or distributor shaft degrees and therefore also called dwell angle.


Abbreviation for Distillers Wet Grains — An animal feed coproduct prior to drying. Typically contains process syrup or at least a portion of the process syrup. DWG is sometimes sold as a final product.
Abbreviation for Driving While Intoxicated
Abbreviation for Deflation warning system
Abbreviation for Deadweight tons
Dykem-type metal bluing
A special blue dye used to check a valve job. When applied to the valve set to show up as a dark ring contrasted against the brightly finished top and bottom cuts, making the seat easier to see and measure
Dykes ring

Dykes ringDykes ring

A Compression piston ring which is L-shaped when viewed from the end. When installed in the piston the horizontal part fits more deeply in the Piston groove while the vertical side rubs against the cylinder wall. This style of ring gives good sealing and prevents piston-ring Flutter during acceleration and deceleration of the piston.

Dykes piston ring
A piston ring with an L-shaped cross section designed to use combustion pressure to improve sealing.
Dynamic balance
When the center line of the weight mass of a revolving object is in the same plane as the center line of the object, that object would be in dynamic balance. For example, the weight mass of the tire must be in the same plane as the center line of the wheel. static balance is made off the vehicle and determined with the tire stationary. Dynamic balance is made with the tire in rotation.
Dynamic ignition timing
Before the introduction of a strobe light, ignition timing was done statically in that the distributor was moved a certain measured amount. With modern engines, a timing light or strobe light is used. It is connected, generally, with the spark plug of the number one cylinder. As power is provided to that cylinder from the coil, the timing light flashes. When the light is projected to the flywheel, the timing marks are illuminated. Moving the distributor will make the timing mark move closer to a fixed mark (retarded) or further away (advanced). Also called Stroboscopic ignition timing. The opposite is Static ignition timing
Dynamic imbalance
Lack of balance in a rotating part such as a wheel, which can cause vibration and shudder
Dynamic seal
Oil seal between a moving and a stationary part. Opposite to Static seal
Dynamic supercharging
The pressurizing of the air/fuel mixture using the natural dynamic behavior of the aspirated air, and not some mechanical device to compress it
Dynamic timing meter
A GM diesel tool used for measuring timing while the engine is running by using a quartz sensor in the combustion chamber that measures the point of combustion and converts this to timing in degrees of crankshaft flotation through the use of a magnetic crankshaft pickup and microprocessor
Dynamic tire balance
The action of making sure that the tire and wheel is in perfect balance can be done in two ways. Both ways involve removing the wheel from the vehicle. In the static method, the tire and wheel are stationary and is placed on a spindle to check for imbalance by using a bubble level, then correcting the problem by placing weights to counteract the imbalance. The dynamic method involves spinning the wheel on a balancing machine which will detect the point of imbalance and recommend the proper weight and location to correct the imbalance.
Dynamic unbalance
A noise-producing condition in an electric motor caused by the nonsymmetrical weight distribution of a rotating member. The lack of a uniform wire spacing in a wound armature or casting voids in a rotor or fan assembly can cause relatively high degrees of unbalance
A British term for a Generator producing direct current.

  1. An electric or hydraulic machine used to measure the actual engine horsepower output and torque. An engine dynamometer measures horsepower at the crankshaft and a Chassis dynamometer measures horsepower output at the wheels.
  2. Device for measuring power output or power input of a mechanism.
A combined generator and starter used on some cars in the 1920s and ’30s, and more recently on two-stroke motorcycles
A combined generator and starter used on some cars in the 1920s and ’30s, and more recently on two-stroke motorcycles
  1. A metric unit of force. 1 dyne of force is applied when a 1 gram object is accelerated 1 cm/s².
  2. A cgs of force, equal to the force required to impart an acceleration of one centimeter per second per second to a mass of one gram.