A
device used to raise a vehicle, usually for changing the tire. Manufacturers
usually provide mechanical screw-type or cissors-type jacks with their
vehicles. Classic cars came equipped with ratcheting bumper jacks.
Another type of jack, the low profile hydraulic jack with wheels is
used by mechanics to raise vehicles.
Jack
stands
Sturdy,
adjustable supports usually shaped like a pyramid used to support
a vehicle once it has been raised by a jack. One should never work
under a car that is supported solely by a jack. Jack stands are much
more sturdy and trustworthy. Never use cement bricks or blocks of
wood to support a vehicle in the air.
Japanese
Industrial Standard (JIS)
A
system of standards use by Japanese manufacturers. Among other things,
they provide horsepower ratings for Japanese and other Asian vehicles
with ratings and measurements similar to those of the SAE and DIN.
Jam(s)
The
region where the chassis and hinged panels such as doors, hood, trunk
lid, rear hatch, and other panels meet. Includes the region on the
chassis that surrounds the opening as well as the edges of the doors
and panels themselves. Also includes the rear, inside region of the
front fenders and tops of the rocker panels. The door hinges, striker
and sill plates (scuff plates on bottom side) mount to the door jams.
Jams are not visible when the panels are closed. Usually contain ridges
where door and trunk weatherstrip fits against when closed. Autobody
technicians often refer to "jamming out a vehicle" to mean
painting all the door, trunk, hood and other panel edges and chassis
openings. Also see Striker.
Jerry
can
A type of rectangular metal container used for fuel, water or other
liquids. Often mounted to the rear of off-road and safari vehicles.
Originated from military use.
Jet
A
calibrated nozzle (usually a hole drilled to specific orifice size)
through which gasoline flows before being mixed with air to produce
an air/fuel mixture. Only a specific amount of fluid can flow through
the varying orifice sizes. Generally there are several jets in a carburetor
- idle, main and power. The main jets are usually replaceable in most
carburetors and racers and street rodders often experiment with different
jet sizes to fine tune for best performance.
Jounce
The
technical term used by engineers for the upward travel of a vehicle's
wheels and suspension such as when it encounters a bump. When the
suspension is pushed downward (by springs) it is called Rebound.
Jounce
bumper
A
heavy-duty rubber cushion usually positioned on the frame to absorb
the impact of suspension components when fully compressed so the metal
parts don't crash together violently which could lead to suspension
damage. Also referred to as a Bump stop or Jounce Stop.
Journal
The
precisely machined flat area of an axle or shaft that is in contact
with a bearing. Used widely to describe the bearing surfaces of a
crankshaft.
Judder
A
technical term for low frequency vibrations that occur when brakes
are applied. Usually caused by slight rotor warpage, rotor damage
or imbalance. Also can occur with clutch systems due to flywheel warpage,
damage or imbalance.
Jumper
cables
Heavy-duty
wires (cables) with spring-loaded clamps on each end used for starting
a car with another battery.
Jump
start
To
use a good battery to help start a vehicle with a weak or dead battery.
Jumper cables transfer the energy from one battery to the other.
Jury
rig
To
assemble in a hasty fashion often from components from other components.
To make work using available components.
