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Glossary of Terms

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All-Wheel Drive (AWD)

A vehicle drivetrain, with all wheels powered by the engine at all times. It is sometimes called full-time four-wheel drive.


A drivetrain that employs two differentials and a transfer case to provide power to all four wheels.

Anti-Lock Brake System (ABS)

Is a computer-controlled braking system that senses an impending wheel lockup, and keeps the tires from skidding during hard braking.While the driver applies steady pressure to the brake pedal, the ABS system automatically "pumps" the brakes many times a second to prevent it. By preventing wheel lockup, it allows the driver to maintain steering control.

Automatic transmission

A transmission that uses a torque converter, planetary gearset and clutches or bands to automatically change a vehicles gears.

Beam Axle

A semi-independent rear axle often used on front-drive vehicles. The horizontal beam, which connects the two rear wheels, can twist to reduce the effect of one wheel's motion on the other. It is less expensive and more compact than fully independent suspension.


The process of removing air bubbles from the hydraulic system during brake pad installation.


The discoloring of cast iron rotors due to heat. Although bluing is evidence of thermal stress, and will lead to reduced rotor life, it is normal under repeated hard braking and is not a cause for concern.

Body Style

The type of exterior shell or shape to a vehicle (sedan, coupe, truck, etc.).

Brake Caliper

A hydraulic (liquid-pressured) piston assembly that holds disc-brake pads.

Brake Drum

The large circular surface that the brake shoe presses against to stop the vehicle.

Brake Fade

The loss of braking efficiency due to excessive thermal stress. The first indication is a distinctive and unpleasant smell. Shift to a lower gear to use more engine braking to slow down.

Brake Pad

Used in a disc rotor system, it is a replaceable piece of high-friction material attached to a metal backing plate.

Brake Pull

Occurs when the vehicle pulls suddenly to the left or right as the brake pedal is depressed. It indicates the brakes may be out of adjustment.

Brake Shoe

A curved, replaceable piece of friction material used on drum brakes. The wheel cylinder pushes the brake shoes against the brake drum.

Coil Spring Suspension

A suspension component made up of spiral-wound hardened steel, used to isolate a vehicle from the up-and-down movement of the wheels on the road.


Generally, a two-door car with close-coupled passenger compartment.


An internal combustion engine in which the air-fuel mixture is ignited by compression in the cylinder rather than by a spark. Diesel engines use diesel fuel rather than gasoline and tend to be more fuel-efficient and require less maintenance than gasoline engines, but it is more complicated to get them to run cleanly. Also used as a slang term: after turning off the ignition, the engine continues to run for a short period.

DIH/Drum in Hat

A disc design in which the internal surface of the hat serves as a brake drum. It is often used as a parking brake.

Disc Brake Rotor

Shiny metal disks made from gray cast iron, called brake rotors, are attached to the wheel hub, rotating with the wheel. When the brake pedal is depressed, the brake calipers squeeze the discs to slow the vehicle.

Drum Brakes

A braking system that uses a metal drum. Brake shoes press against the drum to slow or stop the car.

Electric Vehicles (EV)

Vehicles powered by electricity, generally using a rechargeable battery.

Electronic Brake Force Distribution

A feature of some antilock braking systems that proportions and applies brake force to each wheel independently.

Four-Wheel Drive (4WD)

A transfer case distributes power to both axles in order to drive all four wheels.

Four-Wheel Steering

Vehicle on which all four wheels turn when the driver turns the steering wheel. The rear wheels turn at a smaller angle than the front wheels. This system appeared on a few sports models in the 1980s but was never very popular in North America.

Front-Wheel Drive

Engine power is transmitted to the front wheels, which are the drive wheels.

Factory Equipment

The standard and options that make up the equipment of a used vehicle.


FMSI is an acronym for Friction Material Standards Institute.

Front Brakes Specifications

The dimensions of the major components of a vehicles front brake rotors, and the type of brake ventilation employed.


A car that is usually four doors and seats anywhere from two to seven people.

GVWR - Gross Vehicle Weight Rating

The sum of a vehicles curb weight, cargo weight capacity and passenger weight capacity.

Independent Suspension

A suspension design that lets each wheel move up and down independently of the others. A vehicle can have two-wheel or four-wheel independent suspension; sportier models have four-wheel independent suspension.


Adjective that refers to passenger trucks, as opposed to medium-duty or heavy-duty commercial trucks.

Limited-Slip Differential

A device that helps prevent the drive wheels from skidding or losing traction by diverting power from the slipping wheel to the opposite wheel on the same axle.


The manufacturer of the vehicle (BMW, Chevrolet, Chrysler, Dodge, Ford, GMC, Honda, Toyota, etc.).

Manual transmission

A transmission that varies the power and torque through a foot pedal controlled clutch and a floor-mounted or steering-shaft-mounted gear selection lever.


A medium size car designed to seat four to six passengers.


A specific vehicle brand identified by a name or number (and which is usually further classified by trim or style level).

Model Year

For a vehicle model, the calendar year designation assigned by the manufacturer to the annual version of that model.

OE – Original Equipment

Is an abbreviation for Original Equipment, but it is more correctly referred to as OEM. It is an industry standard term for the equipment that was installed on the model at the time of manufacture.


Is an abbreviation for Original Equipment Manufacturer.


The type of truck with an open cargo bed behind the closed cab.

Rear Brake Type

The type of rear brake: drum or disc.


A two- or four-door car that can hold four to six people. Includes a trunk in the rear.

Solid Disc Brake Rotor

With the solid rotor, the friction surface consists of only one metal disc. This greatly reduces its ability for cooling. Solid discs are usually found on just the rear rotors. Please see tech guide, “Do I have Solid Rotors or Vented Rotors?”

Station Wagon

A two- or four-door passenger car with a cargo area that extends all the way to the rear bumper.


The car size class one step up from the minicar.

Torsion Bar

A simple, rugged type of suspension spring that twists as it is compressed or stretched.

Traction Control

A system for limiting wheel slip under acceleration, thus maintaining each wheel's contact with the road surface. Traction-control systems generally use the anti-lock braking system to stop wheel spin and reduce power from one or more engine cylinders when an electronic sensor detects wheel spin.


The level of options or features added to a vehicle model.

Turbocharged, Turbocharger

A device that compresses and forces extra air into the intake manifold to produce extra power. Both turbochargers and superchargers are used to produce more power without increasing engine displacement, but neither are particularly fuel efficient and both can require costly maintenance as vehicles age.

Two-Wheel Drive (2WD)

A vehicle drivetrain which distributes power to two wheels.

V-Type Engine

In a V-6, V-8 or V-12 engine, the cylinders are divided into two banks, each of which is angled away from the other at the top, forming a 'V.' Typically, this angle is 60 degrees on V-6 engines and 90 degrees on V-8 engines.


A vehicle with six cylinders. The cylinders are divided into two banks, each of which is angled away from the other at the top, forming a 'V.' Typically, this angle is 60 degrees on V-6 engines.


A vehicle with eight cylinders. the cylinders are divided into two banks, each of which is angled away from the other at the top, forming a 'V.' Typically, this angle is 90 degrees on V-8 engines.


A box-shaped truck with a forward cab and a cargo area to the back bumper.

Vehicle Identification Number (VIN)

A seventeen-digit identification number, unique to each vehicle, which includes codes for the manufacturer, year, model, body, and engine specifications.

Vented Disc Brake Rotor

The friction surface of a vented rotor consists of two metal discs held together with vanes of metal which create tunnels that let the heat escape. We call those cooling vanes. Please see tech guide, “Do I have Solid Rotors or Vented Rotors?”

Wheel Size

Determined by the diameter and width of the wheel on which the tire is mounted. A 15-inch wheel has a diameter of 15 inches. A 15 X 7 wheel has a 15-inch diameter and a 7-inch width.