CAUTION
Brake pads may contain asbestos, which has been determined to be a cancer causing
agent. never clean the brake surfaces with compressed air! Avoid inhaling any
dust from any brake surface! When cleaning brake surfaces, use a commercially
available brake cleaning fluid.
Instead of the traditional expanding brakes that press outward against a circular drum, disc brake systems employ a cast iron disc with brake pads positioned on either side of it. An easily seen analogy is the hand brake arrangement on a bicycle. The pads squeeze onto the rim of the bike wheel, slowing its motion. Automobile disc brakes use the identical principal but apply the braking effort to a separate disc instead of the wheel.
The disc or rotor is a one-piece casting mounted just inside the wheel. Some discs are one solid piece while others have cooling fins between the two braking surfaces. These vented rotors enable air to circulate between the braking surfaces cooling them quicker and making them less sensitive to heat buildup and fade. Disc brakes are only slightly affected by dirt and water since contaminants are thrown off by the centrifugal action of the rotor or scraped off by the pads. Also, the equal clamping action of the two brake pads tend to ensure uniform, straight-line stops, although unequal application of the pads between the left and right wheels can cause a vicious pull under braking. All disc brakes are inherently self-adjusting.
There are three general types of disc brakes:
The fixed caliper design uses two pistons mounted on either side of the rotor (in each side of the caliper). The caliper is mounted rigidly and does not move. This is a very efficient brake system but the size of the caliper and its mounts adds weight and bulk to the car.
The sliding and floating designs are quite similar. In fact, these two types are often lumped together. In both designs, one pad is moved into contact with the rotor by hydraulic force. The caliper, which is not held in a fixed position, moves slightly on its mount, bringing the other pad into contact with the rotor. There are various methods of attaching floating calipers. Some pivot at the bottom or top, and some slide on mounting bolts. Many uneven brake wear problems can be caused by dirty or seized slides and pivots.