Disc brakes are the most common brake type used on passenger cars and light trucks today. Repairing this system is a straightforward operation, but there are a few caveats of information to be aware of. The system consists of a disc brake caliper, rotor (or disc), brake pads and anti-rattle clips called hardware.
Calipers
The caliper is the hydraulic portion of the system and provides the clamping force needed to slow or stop your vehicle. It is made up of the housing, caliper piston, square-cut seal and dust boot.
The square-cut seal is the key to proper disc brake function. As the brake is applied, the seal flexes with the pistons movement. When the brake is released, the seal straightens back up and pulls the piston partially back into the bore of the housing. This eliminates rubbing of the pads on the rotors and premature wear of the pads. However, over time the seal becomes hard from normal heat cycling, and even though it may not leak, it will not flex the way it should. Premature pad wear can occur because of this. The simple fix for this problem is to replace or rebuild calipers with every brake job performed.
Rotors
The brake rotors (or discs) are the round metal disc-shaped parts that the caliper clamps the pads onto to slow the vehicle.
Common problems associated with rotors include noise and vibrations caused by warp. This warp is commonly called run out and can be eliminated by resurfacing the rotors. There are minimum thickness specifications for every rotor that must be followed when resurfacing. Machining requires removal of metal, and after the metal is removed, the rotor must still be thicker than the minimum. If not, at some point during the life of the pads, the rotor will be thinner than is safe to use.
Hardware
There are three types of hardware used in disc brakes, but they all serve the same purpose. The purpose is to isolate and absorb vibration. When vibration occurs in the disc brake system, noises like squealing and rattling occur as well.
The three types used are slide shims that give the pad a smooth hard surface to move on, the pad shim that sticks or clips to the pad and isolates it from the caliper, and the spring clip that mounts between the caliper housing and the pads to absorb vibrations. Replacement hardware should be used from time to time to restore their function as they wear.
Pads
Brake pads come in three varieties on passenger cars and light trucks.
The organic brake pad is used on older cars. These pads are made up of particles of bronze and organic material like asbestos and carbon. These pads work in a lower relative heat range than the others. Some rear disc brake applications use the organic compounds as well.
The semi-metallic brake pad is made up of bronze, as well as other metals and manmade fibers like aramid and Kevlar. The ability of these pads to operate at a higher heat range is why they are used on the downsized brake systems of late model cars.
Many newer cars use a ceramic pad, and replacement pads of this design are available for most applications. Their advantage is the high heat they can withstand and quiet operation. Brake dust is reduced but not eliminated, and the dust these pads generate is light gray in color, so it does not show as bad as the dark black dust of the semimetallic.
Summary
Understanding these few things about disc brakes will go a long way in helping to keep your brake system functioning as it was designed to.
