Glossary of Automotive Terms – J

Letter J – Dictionary of Automotive Terms

  1. To lift a vehicle off the ground in order to effect repairs
  2. To steal a vehicle
  3. A characteristic of swing-axle Rear suspensions. cornering forces can act on these suspensions to lift the body of the vehicle so that the outer wheel tucks or jacks under the vehicle. When carried to the extreme, jacking forces could tip the vehicle over.
  4. A device for lifting the vehicle, or part of the vehicle, off the ground to facilitate repairs.
The enclosure on a water heater, furnace, or boiler.

Jacket tube
Jack knife
  1. The action of a vehicle (tractor) with a trailer in which the trailer and the vehicle form a V instead of normally being pulled in a straight line. Usually this is the result of a Skid in which the trailer swings around dangerously and tries to overtake the cab.
  2. Skidding of an articulated vehicle sometimes results in rotation at the articulation (hitch) point so that the tractor is rotated against the trailer in a manner similar to the closing of a jackknife.
  3. To place the trailer at a very sharp angle to the tractor.
Jackson Head
A machine screw with a small oval head.
Jack stand

Jack standJack stand

A safety device that keeps the vehicle from falling to the ground if the lifting jack is removed or faulty. Most jobs require two jack stands for safety. Also called an Axle stand or Safety stand

Jack Staff
A flag staff at the bow of a ship.
Jack up
To raise using a Jack
Jacking point
A strengthened place on the underbody to put the jack. Small cars have one point on each side but larger cars may have two
JaguarClick image for books on

A vehicle brand produced by Jaguar Cars Limited of which the 1946-48 2.5 Litre and 3.5 Litre Mark IV, but not 4-cyl. models are classic cars. The 1957-64 3.4/3.8 Sedans are milestone cars. Includes 1½ Litre saloon (1935-1949), 2½ Litre saloon (1935-1948), 3½ Litre saloon (1937-1948), 240 (1966-1968), 340 (1966-1968), 420 (1966-1968), 420G (1966-1970), E-Type (1961-1974), Mark 1 (1955-1959), Mark 2 (1959-1967), Mark V (1948-1951), Mark VII (& VIIM) (1951-1957), Mark VIII (1957-1959), Mark IX (1959-1961), Mark X (1961-1970), S-type (1963-1968, 1999-2008), Vanden Plas (2002-05), X-type (2001-current), XF (2008-current), XJ (X350) (2003-current), XJ6 Series 1, 2 & 3 (1968-1987), XJ6 (XJ40) (1986-1994), XJ6 (X300 & X301) (1995-1997), XJ8 (X308) (1997-2002), XJ8 (1998-2007), XJ12 (1972-1992), XJ12 (XJ81) (1993-1994), XJ12 (X300 & X301) (1995-1997), XJR (1995-2007), XJR-S (1993), XJ-S (1975-1996), XJ Sport (2002-03), XJ Super (2002-07), XK8 (1997-2006), XK (X100) (1997-2005), XK (X150) (2006-current), XK120 (1948-1954), XK140 (1954-1957), XK150 (1957-1961), and XKR (2000-06)

Jaguar Drophead
A vehicle brand of which the 1951 Mark V Drophead is a milestone car.
Jaguar E-type
Jaguar E-typeClick image for books on
Jaguar E-type

A model of automobile manufactured by Jaguar in England. The 1961-67 E-Type models are milestone cars.

Jaguar Mark
Jaguar MarkClick image for books on
Jaguar Mark

A model of automobile manufactured by Jaguar in England. The 1946-48 models with 2.5 Litre, 3.5 Litre Mark IV (not 4-cyl.) are Classic cars. The 1951-54 Mark VII and ’54 Mark VII M models are milestone cars. The 1956-57 Mark VIII models are milestone cars. The 1958-61 Mark IX models are milestone cars. The 1962-64 Mark X models are milestone cars.

Jaguar XJ
Jaguar XJClick image for books on
Jaguar XJ

A model of automobile manufactured by Jaguar in England

Jaguar XK
Jaguar XKClick image for books on
Jaguar XK

A model of automobile manufactured by Jaguar in England. The 1945-54 XK 110 models are milestone cars. The 1954-57 KX 140 models are milestone cars. The 1958-61 XK 150 models are milestone cars.

Jake brake
A device which shuts off the exhaust valves manually so that in the exhaust stroke, the burned gasses cannot escape through the exhaust valves. Instead they press against the head of the piston and causes the piston to slow down. When the intake valve opens, some of the exhaust escapes out the intake valve and gives a distinctive loud rapping noise. Jake brakes are used in large truck engines to assist in slowing the vehicle. Many municipal bylaws prohibit the use of jake brakes because of the excessive noise. The most common type is called a Jake Brake because the predominant manufacturer is Jacobs Vehicle Equipment Co. Other types of retarders include exhaust retarders, transmission-mounted hydraulic retarders and axle-mounted electromagnetic retarders. Also called a retarder.
A worn-out old car
Abbreviation for Japan Automobile Manufacturers Association
Jamb switch
A push-button light switch located in a door jamb (e.g., for courtesy lights, trunk light)
Jam nut
  1. A second nut (usually thinner) on a screw or bolt which locks against the first nut (i.e., jams against it) so that the nut won’t come loose.
  2. A self-locking nut
Jam on the brakes
The action of quickly depressing the brake pedal (pulling the brake lever on a motorcycle or bicycle) especially in an emergency situation.
Jam the brakes
The action of quickly depressing the brake pedal (pulling the brake lever on a motorcycle or bicycle) especially in an emergency situation.
English engine manufacturer. Founded in 1903 by John A. Prestwich, the company was bought by Villiers in 1957
Japanese lantern-type jacket tube
A web-type jacket tube of a steering column which, on impact, folds like a Japanese lantern
Japanese Motorcycle


Abbreviation for Jet Air System: (Mitsubishi)
JavelinClick image for books on

An automobile manufactured by AMC



A ‘bent bolt’ having the unthreaded end reverse bent to approximately a semicircle.


An abbreviation for Junction, often seen on road signs indicating the distance to a junction with a specified road, for example ‘Jct I-80 26,’ meaning that it is 26 miles to where this road has a junction with I-80.

Jeantaud axle and steering
JeepClick image for books on

A SUV which was originally manufactured by Willys, then owned by AMC, and now owned by Chrysler. Includes Cherokee (1974-83, 1984-2001, 2002-07), CJ (1944-86), Comanche (1986-92), Comanche Pickup (1986-92), Commander (2006-08), Commando C104 (1972-73), Compass (2007-current), DJ (1955-82), FC (1956-65), FJ (1961-65), Grand Cherokee (1993-98, 1999-2004, 2005-07), Grand Wagoneer (1984-91, 1993), J10 Pickup (1963-88), J20 Pickup (1963-88), Jeepster (1948-50), Jeepster Commando C101 (1966-71), Liberty (2002-current), Patriot (2007-current), Super Wagoneer (1966-69), Wagoneer (1963-83, 1984-90), Wrangler (1987-96, 1997-current), and Willys Jeepster VJ (1948-50)

Jeep Dolly
A heavy-duty goose neck dolly usually with two or more axles that support the front of a cradle frame for transporting large objects or a heavy-duty lowboy trailer.
JensenClick image for books on

A vehicle brand of which all 1936-39 models except 2 1/4 Litre 1645 are classic cars



Jerk pump
One of the pumping elements of an in-line injection pump
Jerry rigged
A corruption of the term Jury rigged.
Jersey barriers
Preformed concrete dividers that separate traffic or are used in place of guard rails on some routes.
  1. A small precision-made hole. Often a brass fitting placed inside one of the passages of a carburetor to control the flow of gasoline, air, or air/fuel mixture.
  2. The nozzle containing such a hole.
Jet adjuster
A nut that regulates the volume or strength of the air/fuel mixture in a variable-choke carburetor
Jet bearing
Bearing in a Stromberg carburetor
Jet carrier
A removable plug in a carburetor containing the jet
Jet cooling system
Jet pump is used to produce a vacuum so water or refrigerant may evaporate at relatively low temperatures. These systems usually require large condenser and have a low efficiency to remove heat.
Jet Cutter
Jet fuel
A refined petroleum product used in jet aircraft engines. It includes kerosene-type jet fuel and naphtha-type jet fuel.

Jet head
A removable plug in a carburetor containing the jet
Jet Link
Airport coach service operator.
Jet needle
A tapered needle in a carburetor jet
Jet process
A process by which the thickness of hot-dip galvanized coatings on steel strips can be regulated, allowing the application of coatings of different thicknesses on the two sides of steel strips. When leaving the zinc melting pot, the strip passes two jets through which air, gas, or vapor is directed on the steel strip to remove superfluous zinc. The coating thickness decreases with the strength of the jet
Items that are thrown overboard from a vessel in distress. Discarded cargo that washes ashore.
Jet tube
A tube that houses the main jet in an SU carburetor


The most widely used rim flange type for passenger car wheels; the J-flange is 17.3 mm in height


gate transmission shifterThe center console-mounted transmission shifter in Jaguars. The shifter has the normal pattern down the right side (park, reverse, neutral, low, and drive) while on the left side the driver can select 2nd, 3rd, 4th and 5th manually to have more control over the car. And, no clutch is required.

See Lift Jib.
Lever-type towerjack
Device used in the accurate machining of good in process by holding the goods firmly and guiding tools exactly to position.



Abbreviation for Just-in-Time — a manufacturing system which depends on frequent, small deliveries of parts and supplies to keep on-site inventory to a minimum.

JJD wheel

A safety wheel which can be run when deflated. Two independently inflated tires are seated on a double rim consisting of two single rims. The JJD wheel has excellent aquaplaning properties; a reliable tire pressure control system is required, however, since a defective tire is not easily detectable

A particular piece of work.

Job queue
The lineup of work that a mechanic or shop intends to do in a particular order.
Jockey pulley
  1. On a bicycle, the Pulley in a rear derailleur that stays closest to the freewheel Cogs and guides the chain from Cog to cog during a gear shift.
  2. A free-turning, spring-loaded idler used to keep tension on the timing belt. Also called jockey wheel
Jockey wheel
A wheel used to maintain tension in a chain or belt.

  1. A slight step along the edge of a panel to provide a level mounting and welding surface so that it can be overlapped against the adjacent panel for subsequent lap or spot welding.
  2. To join by means of a joggle
  3. An abrupt bend or offset in a plate, bar, or frame to eliminate the use of liners.
A metalworking tool used for creating a Joggle
Johnson bar
A large portable crowbar used on the dock to pry up heavy freight.
Joiner work ceiling
The overhead finished surface in quarters, etc.
Joining link
Joining Link
  1. The place where two pieces meet when a structure is made of smaller pieces.
  2. A flexible or firm connector between two rods.
  3. Connecting point as between two pipes.
  4. The location at which two adherends are held together by an adhesive.
  5. Points of connection between heat transfer surfaces; between positive and negative pressure zones within components of the power plant; and between power plant components.
  6. The intersection and connection of components, often identified by location within the pallet as the end joint, center joint and corner joint.
Joint boot
Jointed shaft
Joint rate
The common charge for transportation agreed upon by two or more carriers, published in a single tariff, and applying between point on line of one and point on line of another. May include one or more intermediate carriers in route.
Joint rocker arm
Joint separator
Joint socket
Joint splitting tool
Joint steering knuckle
Joint venture
An international business collaboration between foreign interests and private parties from a host country in which two or more parties establish a new business enterprise to which each contributes and where ownership and control are shared.
The effect caused by harsh clutch release. The car body jerks repeatedly in a longitudinal direction
A vehicle brand of which the 1929 – 1931 Models G, 90, Great Line 90, and Speedway Series Z are classic cars.
(J) The international metric unit of measurement of energy, work, and heat. One joule equals the work done when a force of 1 newton moves a body 1 metre. It is one watt-second. Equivalent to 0.737324 ft-lbs.
Joule’s Law
The rate of heat production by a steady current in any part of an electrical circuit that is proportional to the resistance and to the square of the current, or, the internal energy of an ideal gas depends only on its temperature.
Joule-Thomson effect
The change in the temperature of a gas on its expansion through a porous plug from a higher pressure to a lower pressure.
The action of bouncing. When speaking of shock-absorbers, it is the compression stroke while rebound is the opposite.
Jounce and rebound
Jounce buffer
Jounce bumper
An elastic cushion used to stiffen the suspension gradually as it approaches the end of its Jounce travel. Also called jounce buffer.


Jounce bumpers
Elastic cushions used to stiffen the suspension gradually as it approaches the end of its Jounce travel.


That part of a shaft that is prepared to accept and support a bearing. The area on the crankshaft that fits into the lower portion of the Connecting rod. A layer of oil and metal bearing cushions the impact during the Power stroke to prevent the crankshaft from being crushed by the swiftly descending piston and Connecting rod.

Journal, crankshaft
Part of shaft which contacts the bearing on the large end of the piston rod.
  1. A reckless drive in a stolen car.
  2. To go for a joyride
Someone who goes for a joyride


Joint Policy Advisory Committee on Transportation

Abbreviation for Jet mixture solenoid valve

J-type vent tubes

Special tubes located on the top of marine carburetors that direct any overflow from the carburetor bowl(s) back into the throttle bores. USCG-approved method of preventing fire in the engine compartment of the inlet valve sticks in an open position

Jubilee® clamp

Jubilee clampJubilee clamp

A trade name for a band clamp to secure a hose around a fitting. Also called a screw clamp. A screw thread pattern is cut into the band (usually stainless steel). One end of the band contains a captive screw. When the screw is turned, it tightens the band around the hose. Made by L. Robinson & Company (Gillingham) Limited

Jubilee® clip
Another term for a Jubilee® clamp
  1. To shake or vibrate.
  2. Shaking or vibration.
A British term for a very large transport truck (i.e., goods lorry); compare Road train
Juice brake
Juice brakes
A vehicle brand of which models built between 1925 and 1948 are classic cars with required application.
Jumped time
A situation in which ignition or camshaft timing is incorrect because of a mechanical malfunction
A temporary wire leading from one terminal to another

Booster cables
Jumper cables
Jumper cable
Jumper cables
Cables used to start a disabled vehicle by conducting electrical current from the battery of one vehicle to another so that the disabled vehicle can be started and begin to generate it own power. The British term is Jump leads
Jumper wire
A wire used to make a temporary electrical connection.
Jump lead
British term for Jumper cables or booster cables
Jump spark
A high tension electrical current which jumps through the air from one terminal to the other.
Jump start
The act of using Jumper cables on a weak battery to start a disabled vehicle.
A region of transition between semiconductor layers, such as a p/n junction, which goes from a region that has a high concentration of acceptors: (p-type) to one that has a high concentration of donors: (n-type).

Junction block
A device which transfers the action of a single cable to two or more cables.
Junction box
Box or container housing group of electrical terminals.
  1. Scrap; unwanted material, e.g., unwanted car parts.
  2. To scrap, to throw away unwanted material.
Junk ring
A flexible ring used in the cylinder head to provide a seal with the inner sleeve of a sleeve valve engine
A place where cars are sent for scrap. Also called auto graveyard or auto wrecker’s lot.
Jury rig
The action of Cobbling something together instead of put together according to Specifications.
Jury rigged
Something that is Cobbled together instead of put together according to Specifications. An alteration of the expression, Jewry rigged which was a slur on the Jews to indicate poor workmanship.
(JIT) refers to the movement of material to the necessary place at the necessary time. It is part of a business philosophy based on achieving excellence in a manufacturing company through the continuous elimination of waste. A manufacturing system which depends on frequent, small deliveries of parts and supplies to keep on-site inventory to a minimum.
Just-in-time system
A system of production where components are delivered as they are required rather than keeping them in store
Juvenile delinquent
Trucker slang for someone pretending to be a truck driver as in ‘Let’s take it to the double Harley there’s too many juvenile delinquents on this channel.’