How to Check Rear Drum Brakes

In times gone by, drum brake systems were the dominant brake technology in the automotive world. With the advent of superior disc braking technology, together with the associated power-braking technology needed to make disc brakes practical, drum brakes are now found mostly on the rear wheels of less expensive vehicles. Given that many households keep an inexpensive vehicle as a second car, this means that drum brakes are still frequently encountered, and the DIY mechanic can benefit from learning how to check drum brakes.

Instructions

1

Park the vehicle on a firm and level surface. Put automatic transmissions in park, and put manual transmissions in first or reverse gear. Do not engage the parking brake. Securely block the front wheels to prevent vehicle movement.

2

Loosen the lug nuts on both rear wheels about one turn each. Jack up the rear of the vehicle, and set it securely on jack stands. Completely remove the lug nuts, and pull the wheels off both sides.

3

Remove the drums from both rear brakes in such a manner that the brake not being serviced can serve as a visual reference. For some brake designs, the drum can be pulled right off the hub. For other designs, the drum might be fastened to the hub assembly by retaining screws or bolts. If so, remove the retaining fasteners before pulling the drum off. Sometimes the drum is secured with a single large hub nut that must be removed before removing the drum. If the drum is seized, firmly tap the outer shoulder of the drum with a rubber or plastic mallet to loosen it. Sometimes the brake shoes may be pressing on the inside of the drum and preventing its removal. If this is the case, be sure that the parking brake is not engaged. Next, look for a port on the backing plate with a rubber cover. Remove the cover to reveal the brake self-adjuster wheel. Reach inside with a small screwdriver, and rotate the self-adjuster to release tension on the brake shoes. This will back the shoes away from the drum.

4

Measure the thickness of the linings on the brake shoes with a finely-graduated ruler. Compare the measurement to the manufacturer's specified minimum thickness, which can be found in the vehicle's shop manual or aftermarket repair manual. These can usually be found at the local library. Check the brake shoe linings for damage or uneven wear. If the linings are damaged or worn out they should be replaced.

5

Measure the inside diameter of the brake drum in several different directions with the brake drum micrometer. If the drum is round, the diameter will be the same in all directions. Compare the measured diameter to the manufacturer's specified maximum diameter, which is usually stamped into the metal on the outside of the drum. Check the drum for cracks, deep scores, or other damage. If the drum diameter exceeds the allowable maximum, or if the drum is irreparably damaged, it should be replaced. Minor drum damage can be repaired by having the drum machined at an auto parts store.

6

Check the general condition of the brake springs, the self-adjuster mechanism, and the brake cylinder. Replace parts as needed.

7

Reassemble the brake by following the steps in reverse order. Repeat the procedure for the brake on the other side of the vehicle.

8

Lower the vehicle. Start the engine and gently push the brake pedal a few times to extend the cylinders. Try a few stops in reverse to be sure the self-adjusters are properly set. Carefully test the brake operation before driving normally.