The major components of the disc brake system are the brake pads, the caliper, and the rotor (disc). The caliper is similar in function to the wheel cylinder used with drum brakes, and the rotor is similar to the brake drum used in drum brakes.
The major difference between drum brakes and disc brakes is that with drum brakes, the wheel cylinder forces the brake shoes out against the brake drum to stop the car, while with disc brakes, the caliper forces the brake pads inward to squeeze the rotor and stop the car. The biggest advantage of disc brakes over drum brakes is that the caliper and brake pads enclose only a small portion of the rotor, leaving the rest of it exposed to outside air. This aids in rapid heat dissipation, reducing brake fade.
The disc brakes used on Fairmont/Zephyr are known as sliding caliper disc brakes. The name of this system is derived from the sliding action of the brake caliper on the anchor plate during braking. The plate-like brake rotor is attached to, and mounted on, the car by the front wheel hub. A brake caliper anchor plate, attached to the front wheel spindle, mounts over the top of, but does not touch, the rotor. The caliper is mounted in the middle of the large opening in the anchor plate. When the brake pedal is depressed, and hydraulic force is generated, the piston in the caliper forces the inboard brake pad inward and into contact with the brake rotor. The caliper now begins to act like a C-clamp, with the inboard shoe and the piston acting as the adjustable screw. Since there is only a small amount of clearance between the brake pads and the rotor, the inboard shoe contacts the rotor almost as soon as the brake pedal is depressed. As the brake pedal is depressed further, it increases the amount of hydraulic pressure sent to the piston in the caliper. Since the inboard shoe is already in contact with the brake rotor, it cannot be moved. As the caliper pushes on the inboard brake shoe, the increased hydraulic pressure forces the back of the caliper housing away from the back of the piston. This causes the caliper to slide inward on the anchor plate and force the outboard brake pad into contact with the rotor. Thus the name sliding caliper. This happens very quickly, so both pads contact the rotor at about the same time.
When the brakes are released, the piston seal in the caliper housing (which was stretched during brake application) returns to its normal position and, in so doing, pulls the piston away from the brake pad. A very slight wobble in the rotor as the car begins to move pushes the brake pads back so they are not in contact with the rotor. The clearance between the pads and the rotor is very slight, but it is sufficient to prevent brake drag. The same clearance is maintained even when the brake pads wear as the car accumulates mileage and, because of this, disc brakes do not need to be adjusted.