jack: [1] A device for lifting the vehicle, or part of the vehicle, off the ground to facilitate repairs. The most common jacks are the bumper, tripod, scissors, and hydraulic jacks. [2] 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.

jacket: See water jacket.

jack knife: 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.

jack 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.


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.

JAMA: Acronym for "Japan Automobile Manufacturers Association"

jam nut: A second nut on a screw which locks against the first nut (i.e., jams against it) so that the nut won't come loose.

jam on the brakes: !!! Definition under construction !!!.

jam the brakes: !!! Definition under construction !!!.

Jensen: The 1925-1948 models with required application are classic cars.

jerry rigged: A corruption of the term "jury rigged."

jet: A small orifice. Often a brass fitting placed inside one of the passages of a carburetor. See compensating jet and metering jet.

jigs: device used in the accurate machining of good in process by holding the goods firmly and guiding tools exactly to position.

JIT: Acronym for "Just-in-Time."

jockey pulley: 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.

joint: [1] Where two pieces meet when a structure is made of smaller pieces. [2] A flexible or firm connector between two rods. See ball joint, ball joint rocker arm, ball joint steering knuckle, cardan joint, constant velocity joint, slip joint, splined joint, and universal joint.

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.

Jordan: Only the Speedway Series 'Z' of 1925-1948 are classic cars.

joule: The international unit of measurement of energy, work, and heat. One joule equals the work done when a force of 1 newton moves a body 1 meter.

jounce: The action of bouncing. When speaking of shock-absorbers, it is the compression stroke while "rebound" is the opposite.

jounce bumper: An elastic cushion used to stiffen the suspension gradually as it approaches the end of its jounce travel. Also see bump stop.

jounce bumpers: Elastic cushions used to stiffen the suspension gradually as it approaches the end of its jounce travel. Also see bump stop.

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

juice brake: See hydraulic brakes.

juice brakes: See hydraulic brakes.

Julian: The 1925-1948 models with required application are classic cars.

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 to start a disabled vehicle.

jumper cable: See jumper cables.

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.

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.

just-in-time: (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.