Brake Glossary
Annulus: The height of a brake disc/rotor, from the hat to the outside of the rotor.
Anti-lock brake system: A type of braking system that senses the speed of each wheel and, in conjunction with a computer, controls the hydraulic braking pressure, thereby eliminating wheel lockup.
Anti-lock brake control module: The computer used to control an anti-lock braking system.
Backing plate: Stamped steel plate upon which the wheel cylinder is mounted and the brake shoes are attached; a metal plate that serves as the foundation for the brake shoes and other drum brake hardware.
Belleville washer: A circular disk formed into a conical shape. When a load is applied, the disk tends to flatten, constituting a spring action. May be referred to as a coned-disk spring.
Bench bleeding: A procedure used to bleed the air from a new or rebuilt master cylinder before it is installed in the vehicle.
Binders: A term used for brakes.
Bleed:
- To drain fluid.
- To remove an air bubble or air lock.
Bleeder screw: A small, hollow screw or valve found at drum-brake wheel cylinders, in disc brake calipers, and adjacent to the outlet ports of some master cylinders. It is opened to release pressure and to bleed air and fluid from the hydraulic system.
Bleeding:
- The slow releasing of pressure in the air-conditioning system by recovering some of its liquid or gas.
- The act of removing air from a hydraulic brake system.
- A small leak.
- When one paint color shows through another.
Brake bias: The ratio of braking force of the front end of the vehicle compared to the rear. An excessive brake force at either end of the vehicle can cause the brakes at that end to lock before the other end, often leading to loss of control.
Brake bleeding: Procedure for removing air from lines of a hydraulic brake system.
Brake booster: A device that uses a supplementary power source to reduce pedal force in a hydraulic brake system.
Brake disc: The parallel-faced, circular, rotational member of a brake, acted upon by the friction material of the shoes. Also known as a brake rotor.
Brake disc minimum thickness: A term sometimes used to indicate disc minimum thickness.
Brake dive: A term used for dive.
Brake drag: A light, but constant, contact of the brake shoes with the drum or rotor, resulting in early failure due to excessive heat.
Brake fade: A condition whereby repeated severe application of the brakes, over a short time period, cause an expansion of the brake drum and/or loss of frictional ability, which results in impaired braking efficiency.
Brake feel: A term relating to the driver's ability to determine the amount of braking force exerted or required during a stop.
Brake fluid: A specially formulated liquid used to transmit brake pedal pressure from the master cylinder to the wheel cylinders.
Brake flushing: The removal of fluid from a brake system, washing out sediment by flushing with denatured alcohol or clean brake fluid, and refilling the system with fresh brake fluid.
Brake light switch: An electrical switch, operated either mechanically or hydraulically when the brakes are applied, that causes the brake lights to light up.
Brake line: Small-diameter, rigid-steel tubing, or flexible, rubber, reinforced hose, used to channel brake fluid from the master cylinder to the wheel cylinders or calipers when the brakes are applied.
Brake pad: The pad of friction material applied by the caliper to the disc, to slow or stop a vehicle.
Brake stopping distance: The distance traveled from the application of the brakes to the point at which the vehicle comes to a complete stop.
Brake warning light: An instrument-panel light that warns of brake-system malfunction.
Braking force (torque): The force that actually decelerates the tire and wheel.
Caliper: Non-rotational components of disc brakes that straddle the disc and contain hydraulic components forcing the brake pads against the rotor to slow or stop the vehicle.
Carrier: A part that holds, positions, moves, or transports another part or parts.
Disc brake: A type of brake that provides a means of slowing or stopping a vehicle using hydraulic pressure to apply pads against a rotor.
Disc-brake fluid: A special fluid having a high boiling point, about 500°F (260°C). If exposed to air, it will attract moisture and be unsafe for use.
Disc-brake pad: An assembly consisting of friction material and its steel backing.
Disc minimum thickness: The least thickness, usually stamped or cast into the disc, to which a brake disc can be machined or worn before it becomes unsafe.
Disc run-out: The amount that a brake disc wobbles during rotation.
Dry boiling point: The temperature at which a given brake fluid boils when the fluid is fresh (out of the can).
Dual master cylinder: A master cylinder, associated with a dual-brake system, having two sections for displacing fluid under pressure; generally one section for front brakes and one section for rear brakes or, in some applications, one for left brakes and the other for right brakes.
Emergency brake system: A brake system used for stopping a vehicle in the event of a malfunction in the means of operation and control of the service brake system.
Fixed caliper: A disc-brake caliper that does not float or slide, rigidly mounted to the steering knuckle, spindle, or control arm, having one or two pistons on each side of the disc.
Floating rotor: A multi-piece brake rotor that has oblong holes instead of straight holes cut into the rotor flange to allow for thermal expansion and self-centering.
Hydraulic brakes: A braking system using hydraulic pressure to press the brake pads against the brake discs.
Lockup: The point at which braking power overcomes the traction of the vehicle's tires and skidding occurs, causing loss of control, long stopping distances, and flat-spotting of the tires.
Master cylinder: A brake-system component having an integral reservoir filled with hydraulic brake fluid where pressure is developed when the driver depresses the brake pedal causing a linkage to move a piston.
Minimum thickness: The lower limit of the thickness required after metal has been removed from an item such as a brake disc, to retain its integrity.
Organic friction material: A friction material having organic binders substantially formulated with nonmetallic fibers.
Out of round: The condition of a circular part when it is not circular, as in slightly oval shaped.
Pad: A brake lining and metal back riveted or molded together. Two pads provide stopping friction by rubbing against both sides of a rotor or inside a drum when the brakes are applied.
Pad-wear indicator: A mechanical or electrical warning device on disc brakes that indicates need for pad replacement.
Parking brake: A mechanically applied brake system, usually to the rear wheels or drive shaft, to prevent a parked vehicle's movement.
Parking-brake cable: A cable or cables that transmit brake-actuating force in the parking-brake system.
Parking-brake system: A brake system, intended to hold a vehicle stationary, in which one or more brakes may be held in the applied position without continued application of force to the control.
Piston: round, caliper component in a disc brake that is moved outward by fluid pressure to press the pads against each rotor face.
Pressure bleeder: A device used to facilitate the removal of air from the brake system.
Pressure bleeding: Bleeding the brake system using a pressure bleeder to charge the system.
Proportioning valve: A valve in the brake hydraulic system that reduces pressure to the rear wheels to achieve better brake balance.
Pulsation: A surge that may be felt in the brake pedal during low-pressure braking.
Rotor: Disc-shaped component that revolves with hub and wheel. The lining pads are forced against the rotor to provide a friction surface for the brake system, so as to slow or stop a vehicle.
Splash shield: A stamped sheet-metal deflector plate located behind the disc-brake rotor providing component protection from dirt and water and improving the flow of air over the rotor.
Spongy brake pedal: A condition where the brake pedal is not solid when depressed, but bounces softly. This is caused by air in the hydraulic lines, distortion or stretching of the connecting parts, or swelling of the hydraulic hoses.
Ventilated rotor: A disc-brake rotor whose friction surfaces are separated by cooling fins having open, ventilated passages between each face for heat dissipation.
Wet boiling point: The temperature at which a given brake fluid boils after the fluid has been exposed to moisture and has had the opportunity to absorb water.
