About Brake Calipers
There are two types of brake calipers used on automobiles today. The more common is the floatingcaliper and the lesser common the fixed caliper. A big difference between a floating caliper and a fixed is the floating caliper rides on two pins mounted to the steering knuckle, while the fixed caliper mounts directly to thesteering knuckle. Both of these units react from hydraulic pressure from the master cylinder.
A floating caliper uses one piston and the caliperhousing to clamp down on the rotor. First the piston moves the inboard pad to contact the inner side of the rotor. The force of the inboard pad contacting the inside surface of the rotor causes the caliper to slide or float on the pins mounted to the steering knuckle. This forces the outboard pad mounted inside the caliper housing to contact the outer side of the rotor. This clamping force on the spinning rotor is what causes the wheel to stop. The pins can stick in their bores preventing sufficient braking force and causing the inboard pad to wear prematurely.
A fixed caliper has pistons on both sides of the rotor. These pistons squeeze both the inboard and outboard pads with equal force causing the vehicle to stop. Brake caliper pistons are made of either chrome platted steel or phenolic plastic. Both of these are usually hollow to save weight. The phenolic pistons are great heat insulators and thus help prevent heat from degrading the brake fluid.
A seal is used to contain fluid pressure and to help return the piston to its released position after brake application. The seal distorts and bends as the brakes are applied. When the pressure is released the seal returns to its original position bringing the piston with it. This allows the pads to release a short distance away from the turning rotors while the vehicle is moving forward.
