Automotive Terminology & Definitions

see 'anti-lock brake system "

a component located on the brake backing plate, on which the brake shoes rotate and to which the return springs are secured.

a computer controlled system that allows the vehicle to be controlled under heavy braking by releasing hydraulic pressure to wheels that are about to lock up and skid. Sensors located at the wheels, monitor rotating wheel speed in relation to other wheels and send the information to a control module that in turn controls a hydraulic modulator, which regulates hydraulic fluid pressure to each brake assembly.

ABS keeps the wheels from fully locking up while braking to allow the driver to maintain steering control. Without ABS, too much force applied to the brake pedal can cause one or more wheels to stop turning (lockup) and begin skidding, greatly reducing the capability of the driver to steer. With ABS, maximum force on the brake pedal slows each wheel to the point of maximum braking - without skidding.
Since all wheels are still rolling, the driver maintains steering control within the limits of traction. Many light trucks use rear-wheel ABS to prevent rear wheel lockup.

the component to which the brake shoes, wheel cy/inder and related components are attached.

a valve located on disc brake calipers, wheel cylinders and some master cylinders that allows air and fluid to be removed from the brake system.

a condition that occurs when brake pads or shoes are in continuous contact with the disc brake rotors or brake drums.

a round cast iron housing attached to an axle shaft or spindle, on which the brake shoes press to stop its rotation.

phenomenon that takes place when the temperature of the friction surfaces increases to a point where the application of heavy pedal pressure results in little braking action.

the hydraulic fluid used to transmit hydraulic pressure through the brake lines in a brake system.

a procedure to clean the brake hydraulic system with fresh, clean fluid that should be performed whenever new parts are installed, if there is any doubt as to the grade of fluid in the system, if a glycol fluid has been mixed with a silicone-based fluid, or if the fluid has been contaminated with petroleum or mineral based fluids.

flexible hoses that connect the brake lines on the chassis with the calipers or wheel cylinders, or the junction block on a solid axle.

metal tubing that carries the brake fluid from the master cylinder to other brake system components.

see 'disc brake pad'.

see 'disc brake rotor'.

friction material that is bonded or riveted to curved metal structures and attached to the backing plate. The brake shoes press on the brake drum to stop its rotation.

the process of polishing a part using the pressure of a sliding tool.

a ragged metal edge left on a part during machining.

see 'disc brake caliper'.

damage or wearing away caused by friction and rubbing.

a bevel or taper at the edge of a hole or corner, usually cut at 45 degrees.

the specified distance between two components.

a single unit in the hydraulic brake system that incorporates the metering and proportioning valves in conjunction with the pressure differential switch. Combination valves are categorized as being either two-function or three-function devices, depending on the number of functions they perform. A threefunction valve provides all of the aforementioned capabilities of metering, proportioning and warning. However, the two-function unit combines either the proportioning and warning light functions or the metering and warning light operations into a single component.

an opening between the master cylinder bore and reservoir that allows brake fluid to return to the reservoir.

a reduction in size, drawing together, narrowing, shrinking or shortening; the opposite of expansion.

a means through which information about the state of the vehicle control system can be extracted with a scan tool. This information includes actual readouts on each sensor's input circuit and some actuator signals. It also includes any trouble codes stored. The data link connector is also used to disable the computer's ignition timing adjustments on some engines so base or reference timing can be measured with a timing light. Before OBD II, each OEM had a unique Data link Connector (DLC) and :alled it by a different name. With the advent of OBO-II, the DLC became standardized as a 16-pin connector to which the scan tool could be connected to read data and sometimes control outputs of the PCM.

a hydraulically actuated device in a disc brake system that is mounted straddling the brake disc. The caliper contains at least one piston and is used to provide clamping force of the brake pads on the disc.

friction material that is bonded or riveted to metal plates and mounted in the disc brake caliper. The brake pads are clamped against the disc brake rotor to stop its rotation.

a cast iron disc mounted on the wheel hub, which is clamped by the caliper and disc brake pads to slow and stop its rotation.

a braking system that uses cast iron discs mounted on the wheel hubs, over which brake calipers are mounted. Hydraulic pressure from the brake system forces the caliper piston(s) against friction pads mounted in the calipers, which in turn clamp the brake discs, stopping their rotation.

warp, twist or other deformation in a part.

department of transportation.

a braking system that uses cast iron drums mounted to the wheel hubs. Hydraulic pressure from the brake system forces pistons in the wheel cylinder to press friction lined brake shoes against the inside of the drum, stopping its rotation.

a master cylinder that has one cylinder bore, but two pistons and two fluid reservoirs. Each piston applies hydraulic pressure to two wheels only. In the event one of the hydraulic circuits fails, the other provides enough braking power to stop the vehicle.

a drum brake design that provides increased stopping power due to the servo or self-energizing action of the brake shoes.

operates in conjunction with ABS to balance the force applied to brakes at front and rear wheels. Can prevent over-braking, improve brake-pad life, reduce "brake fade" caused by excessive heat, and ensure peak braking efficiency in all conditions.

the computer in an electronic control system, also known as an electronic control unit (EGU).

see 'electronic control module (ECM)'.

the next logical evolution of ABS and traction control. It has ABS's hardware and two additional sensors: steering-wheel angle sensor, which measures the position and rate the steering-wheel is turning, and a yaw sensor, which measures the rate the vehicle is actually turning. By comparing them, the on-board computer will know if the vehicle is oversteering or understeering.

thin metal strip manufactured in precise thickness and used to measure clearance between parts; usually part of a set.

a brake caliper design that contains one or two pistons positioned on either side of the rotor. The caliper is rigidly attached to the spindle and the pads are applied with equal hydraulic pressure from both sides..

a type of brake caliper seal that is installed in a groove in the caliper bore.

a brake caliper design that uses an adapter, or anchor plate, which is bolted to the spindle. The caliper floats laterally across a pair of special bolts that are screwed into the adapter. As hydraulic pressure is applied to the piston, the inboard pad is forced against the rotor. This pressure causes the caliper to move inboard until an equal pressure is applied by the outside pad to the outer disc surface.

the resistance to the motion of two moving objects in contact with each other.

a measuring tool that tells if a tolerance is met or not.

in area in a casting which has become harder (more dense) than the surrounding material; areas in the friction surface of a brake drum or rotor that have become harder than the surrounding metal.

springs that are used to keep the brake shoes secured to the backing plate.

pressure exerted through a liquid.

a power brake system that uses power steering pump fluid pressure rather than intake manifold vacuum.

the ability of a material or substance to attract water.

inside diameter.

inner part of a ball or roller bearing that provides a surface for the balls or rollers to rotate.

an anti-lock braking system that substitutes the traditional master cylinder and power booster with a self-contained hydraulic modulator and high-pressure accumulator.

a non-servo drum brake system where both brake shoes are held in place against a solidly attached anchor mounted to the bottom of the backing plate.

the primary fluid pressurizing device in some hydraulic systems. In automotive use, it is found in the brake and hydraulic clutch systems and is pedal-activated, either directly or through a vacuum assist unit.

a valve used on front disc/rear drum brake systems for the purpose of providing a simultaneous application of the front and rear friction materials. Located in the front brake hydraulic circuit, the metering valve delays front disc brake operation until the rear brakes shoes overcome the return spring tension.

the base of metric size measurement. One millimeter equals 0.039370-in. One inch is equal to 25.4 m m.

a component in the ABS system that contains the solenoid valves that regulate hydraulic fluid pressure to the calipers or wheel cylinders.

the average expected wear when operating under normal conditions.

original equipment manufacturer.

the process of combining with oxygen, resulting in rusting or burning. Rust is slow oxidation; fire is rapid oxidation.

a system that applies the brakes mechanically through a series of linkages and cables. Depending on the vehicle, the parking brake system will either be actuated using a foot pedal or a hand-operated lever.

the law of physics stating that liquids are noncompressible, and that a force applied to the top of a liquid in a closed container is exerted equally in all directions.

ability of a membrane or other material to permit a substance to pass through it.

surface irregularities caused by corrosion or excess wear.

the relative movement between or among parts.

a device that uses a diaphragm, engine vacuum and atmospheric pressure to assist the driver with brake application. Also known as a vacuum booster.

a system that uses vacuum or hydraulic pressure to assist the driver with brake application.

tightening a bearing a specified amount past zero lash to eliminate axial play.

a valve and switch assembly installed in dual circuit brake systems to alert the driver in the event of a pressure loss in one of the hydraulic circuits.

the brake shoe in a duo-servo drum brake system that transfers part of its force to the secondary shoe. The brake shoe facing the front of the vehicle when the vehicle is moving forward.

the proportioning valve is used to control hydraulic pressure to the rear brakes. When the pressure to the rear brakes reaches a predetermined level, the proportioning valve overcomes the force of its spring-loaded piston and stops the flow of fluid to the rear brakes. This action maintains rear brake system pressure at a lower level than the front brakes, keeping the rear brakes from locking during hard stops.

a master cylinder design that is used to prevent excessive brake pedal travel. The quick take-up master cylinder uses a larger rear cylinder bore and quick take-up valve. This arrangement provides a large volume of fluid at low pressure (light pedal application) during the initial part of the pedal stroke. Also called a step-bore master cylinder.

a channel in the inner or outer ring of an anti-friction bearing in which the balls or rollers operate.

process of recovering some of a hybrid or electric vehicle's kinetic energy by allowing the wheels to drive a traction motor as a generator, thereby producing electric power that is stored for later use. When the driver brakes, the motor becomes a generator, using the kinetic energy of the vehicle to generate electricity that can be stored in the battery for later use. Traditional friction brakes are also necessary, as well as a strategy for smoothly blending the two braking mechanisms. Regenerative and friction brakes need to be controlled electronically so that stopping ability is maximized to make the dual brake operation transparent to the driver.

remaining or leftover pressure.

springs that secure the tops of the brake shoes to an anchor pin on the backing plate. These springs allow the shoes to move in and out laterally.

the brake shoe in a duo-servo drum brake system that receives force from the primary shoe when the brakes are applied. The secondary shoe does most of the braking when the vehicle is traveling forward, so its lining is larger than that of the primary shoe.

a mechanical, electrical, hydraulic or electromechanical device which transmits information to a gauge or other receiving unit.

a device, such as an electric motor or hydraulic piston, that is controlled by an amplified signal from a low power command device.

a brake caliper design that operates similarly to the floating design, however, it attaches to the anchor plate using only one attachment point.

the feel of a soft or mushy brake pedal usually caused by trapped air in the hydraulic system.

the star shaped wheel that is attached to the screw of a drum brake shoe adjuster. If brake shoe-to-drum clearance is excessive, the wheel is turned by the self-adjuster lever when the brakes are applied with the vehicle in reverse, moving the brake shoes closer to the drum.

a gradual decrease in width or thickness; the difference in diameter between the cylinder bore at the bottom of the hole and the bore at the top of the hole, just below the ridge.

information published by vehicle manufacturers that describe updated service procedures and service procedures that should be used to handle vehicle defects.

stress exerted on an object by pulling that tends to extend the material.

the difference between the allowable maximum and minimum dimensions of a mechanical part; the basis for determining the accuracy of a fitting.

a specified order in which a component's mounting bolts should be tightened

a breaker bar or ratchet wrench with an indicator that measure the twisting effort applied to a fastener during tightening.

twisting effort on a shaft or bolt.

when an inside or outside diameter has been machined to a dimension smaller than standard. Undersized bearings are used to compensate.

see 'power booster'.

a device that controls the pressure, direction or rate of flow of a liquid or gas.

a condition that exists when a part is bent or twisted; the degree to which a part deviates from flatness.

a cylinder connected to a drum brake hydraulic system. Hydraulic pressure in the system applies piston(s) in the wheel cylinder against the brake shoes, forcing the shoes against the inside of the brake drum and stopping its rotation.