Disc Brake

Disc brakes use a clamping action to produce friction between the wheel and the suspension members which hold the wheel. Firmly mounted to the spindle, the caliper works like a c-clamp to pinch the rotor which is attached to the spinning wheel. "Floating" calipers allow themselves to move slightly when the brakes are applied, because only one pad moves (in relation to the caliper). If the caliper is solid-mounted, there are pistons on each side of the rotor. These are called "dual cylinder" or "dual piston" calipers, and are standard equipment on many performance cars. Inside the caliper, the piston(s) press against the pads due to the pressure generated in the master cylinder. The pads rub against the rotor, slowing the vehicle. Because disc brakes can fling off water more easily than drum brakes, they work much better in wet conditions. They allow better airflow cooling, which also increases their effectiveness. Some high performance disc brakes have drilled or slotted holes through the face of the rotor, which helps to prevent the pads from "glazing" (becoming hardened due to heat). Disc brakes were introduced as standard equipment on most American cars in the early seventies. The disc (rotor) is a heavy plate that attaches to the spindle to provide a two-sided braking surface. Fluid from the brake line flows into a cylinder mounted on the side of a clamp-like caliper. Part of the fluid pressure is exerted against a piston, which forces the brake shoe and pad against the inside surface of the disc. The fluid also exerts pressure in the other direction against the back of the cylinder. This back pressure causes the whole arm of the caliper to move sideways, bringing an outboard shoe and pad tight against the outside of the disc to provide additional stopping power. Ventilation slots around the outside rim of the disc allow friction heat that is generated to be transferred to the air quickly.