Although disc brakes have been around for decades, many cars and light trucks still have drum brakes on the rear. Why? Because drum brakes are less expensive to manufacture, are self-energizing (they don’t require as much pedal pressure or power assist) and can easily incorporate a simple parking brake mechanism.
On vehicles that have disc/drum brake systems, the front disc brakes do most of the work. Consequently, the disc brake pads up front usually wear out two to three times faster than the drum brake shoes in the rear. Because of this, the rear brake linings and hardware may only be inspected rather than replaced when a vehicle receives its first or second brake job.
By the time the rear linings are worn out, most drum brakes have seen a lot of miles. The hardware inside the drum is usually in poor condition and should be replaced. Drum brake hardware includes:
● Return springs that retract the shoes away from the drums when the brakes are released. These may weaken and stretch with age, allowing the brake to drag rather than turn freely when the brakes are released.
● Hold-down springs retain the shoes and allow the shoes to move sideways on the brake backing plate. A broken spring can allow unwanted shoe movement inside the drum. It also may cause noise or wedge itself between the shoe and drum causing the brake to drag or seize.
● Adjuster spring(s) help maintain tension on the self-adjuster so the adjuster can compensate for shoe wear.
● Self-adjuster mechanism compensates for brake wear to brake pedal play doesn’t increase as the linings on the brake shoes wear down. Corrosion and dirt can often jam a self-adjuster and prevent it from working.
● Parking brake adjuster cable works with the parking brake linkage to push the shoes outward against the drum when the parking brake is applied.
Disc brakes also have hardware that’s just as important as drum hardware. There are no hold-down springs, return springs or adjusters, but disc brake calipers do have slides, mounting pins and bushings that can cause problems if the hardware is worn, badly corroded or damaged.
In a typical single-piston floating caliper, the caliper slides inward as the piston pushes the inner pad out against the rotor. If the caliper fails to slide because the mounting hardware is worn or corroded, the caliper will not move and force the inner brake pad do all the work. This will cause the inner pad to wear rapidly and also reduce braking effectiveness. Also if the caliper moves inward but fails to slide back to its original position, the pads can drag against the rotor. Replacing the hardware and lubricating the slides with high temperature brake grease (never ordinary chassis grease) will assure normal operation and smooth, even braking.
Other “hardware” that also may need replacing on disc brakes includes the clips, shims and/or insulators that secure the pads in the caliper. Loose or missing anti-rattle clips, shims or insulators on the backs of pads may contribute to a noise problem. In fact, anything that increases pad vibration can amplify brake noise, particularly with semi-metallic pads.
When new pads are installed, they must be held securely by their positioning ears and/or anti-rattle springs, clips or insulator shims, otherwise they can vibrate and chatter. Installing a dampening shim or applying a noise control compound or adhesive to the backs of the pads will help keep them quiet.
