For the most part drum brake technology has been replaced by disc brake technology on the front wheels of modern automobiles; however drum brakes are still used on the rear wheels inexpensive vehicles in order to keep the cost down. Drum brakes are complicated mechanical devices, and as such they are not as reliable as disc brakes. There are a number of potential problems that can cause the brake shoes to seize or stick. The first step in correcting a stuck brake shoe is to determine why the shoe is sticking.
Park the automobile on a flat, level surface. Put automatic transmissions in "park," and manual transmissions in first or reverse gear.
Set the emergency brake. It should normally take six to ten clicks of pedal or lever travel to engage the brake, and the pedal or lever resistance should increase the further it is moved. If only a couple of clicks of pedal or lever travel is needed to set the brake then the brake is set too tight. Correct by loosening the emergency brake adjusting nut located at the base of the lever or at the top of the pedal. If the secondary brake shoe is sticking against the drum, or if the emergency brake cable is seized then the parking brake lever or pedal will feel slack until the parking brake suddenly engages.
Replace the emergency brake cables if seized. Completely remove the emergency brake adjusting nut. Remove the retaining clip on the emergency brake cable end at the secondary brake shoes on both wheels and slip the cables out from the shoes. Slide under the car and unbolt and remove the brackets that hold the cables. Remove the cables. Install new cables by following steps in reverse order.
Release the emergency brake and securely block the front wheels to prevent the vehicle from rolling. Loosen the lug nuts on both rear wheels about one full turn each. Jack up the rear of the automobile and support it on safety stands. Finish removing both rear wheels.
Remove both brake drums. On some vehicles the drums are held by two to four bolts, while on others the drums are held by two to four large screws or by nothing at all. Remove any retaining bolts or screws and pull the drums straight off the hubs. If the drum rim is seized to the backing plate tap the drum firmly with a mallet on the outer shoulder to loosen. Take care to not hit the drum rim where it meets the backing plate. Also, some brakes have an access hole covered with a rubber plug near the bottom of the drum or backing plate that allows access to the adjuster mechanism. If the drum is caught on the brake shoes then remove the rubber plug, reach through the access hole with a small screw driver and turn the adjuster wheel to retract the brake shoes a little.
Examine the brake mechanism springs on both wheels. There are two return springs connecting the front and rear brake shoes, and if either of these is broken or weakened then the shoes will not retract fully, causing them to drag on the drum. Replace any suspect springs by gripping one end of the spring with pliers and unhooking it from its mounting, and then unhooking the other end in a similar manner.
Hold the adjuster lever off the adjuster wheel and turn the wheel back and forth. If the adjuster wheel is seized or at the end of its travel it may be forcing the shoes to drag on the drum. Remove the brake return springs and the adjuster lever spring, and slide the adjuster wheel assembly out from between the shoes. Unscrew the assembly and lubricate the threads with brake grease. Reassemble the parts in the reverse order.
Look for corrosion or accumulations of dust and dirt. Heavy deposits where the shoes contact the backing plate, or around the pivot points for the adjuster lever, the operating lever, and the brake retaining pins can seize the brake mechanism and prevent the shoes from retracting normally. Clean any dust and dirt by spraying with brake cleaning fluid and working the dirt off with rags or a wire brush. Lubricate the pivot points and contact points with brake grease.
Observe the brake cylinder operation while an assistant starts the automobile and gently pushes the brake pedal a few times. Do not pump the brakes. Allow about five seconds between each push on the brake pedal. The cylinder piston should extend when the pedal is pushed and retract when the pedal is released. A defective cylinder can remain extended and hold the shoes against the drum.
Reassemble the brake by following disassembly steps in the reverse order. Lower the vehicle.
Do not inhale brake dust or break cleaning fluid vapours. Use a catch pan to collect used brake cleaning fluid and dispose of in accordance with local regulations.
Tips and warnings
- Do not inhale brake dust or break cleaning fluid vapours.
- Use a catch pan to collect used brake cleaning fluid and dispose of in accordance with local regulations.