Drum brakes appear complicated, but service procedures are within the capability of novice mechanics.
Drum brakes are quickly becoming an anachronism in the automotive world. The once-dominant braking technology has been largely supplanted by modern disc brake systems. Disc brakes perform better than drum brakes, and their simplicity makes them more reliable and easier to maintain. Regardless, drum brakes are still less expensive, and because of this they are still found on the rear wheels of many inexpensive vehicles, and the DIY mechanic will find it useful to learn repair drum brakes.
Instructions
1. Park the vehicle on a firm, level surface and securely block the front wheels. Put automatic transmissions in park, and put manual transmissions in first or reverse gear. Leave the parking brake off. Partly loosen the lug nuts on both rear wheels then jack the rear of the vehicle and support securely on jack stands. Completely remove the lug nuts and pull the wheels off both sides.
2. Remove both brake drums so the drum not being serviced can be used as a reference. On many vehicles it will pull right off the hub, however sometimes it may be held to the hub assembly by retaining screws or bolts. If so, remove the retaining fasteners before pulling the drum off. The drum may also be held by a large hub nut, in which case this must first be removed before removing the drum. If the drum is seized to the backing plate, as is often the case, firmly tap the drum with a rubber or plastic mallet to loosen it. Take care not to hit the drum so hard that it cracks.
Sometimes because of a weak return spring, a fully extended self-adjuster, or a malfunctioning parking brake the shoes may be pressing on the drum and preventing its removal. If this seems to be the case look for a hole on the drum or backing plate with a rubber cover. Open the cover and you should see the adjuster wheel teeth. Reach inside with a small screwdriver or pick and rotate the adjuster to release tension on the brake shoes. If the parking brake is the culprit then locate the parking brake cable tensioner bolt and loosen it. On larger vehicles it is often under the car on the driver's side, while in smaller vehicles it is often at the base of the hand brake lever inside the passenger compartment.
3. Remove the springs. The various brake springs are hooked at each end, and removal consists of gripping one end of the spring with pliers and unhooking it. With the spring tension relieved it is easy to unhook the other end. Using vice grip pliers makes the job easier since you can lock the vice grips onto the spring end and then concentrate on pulling to unhook the spring end without having to also worry about keeping your grip. There are special brake spring tools available, but these tend to work well for some springs and not for others and most mechanics prefer to use pliers.
First remove the large return springs that connect the front and rear brake shoes. If these are very difficult to remove it often helps to first rotate the self-adjuster mechanism to relieve some of the tension on the shoes. Some brake designs use separate springs from the upper end of each shoe that anchor on a single pin above the cylinder, rather than a single return spring directly between the two shoes in the upper position. After removing the large return springs, remove the smaller springs for the adjuster mechanism pawl (ratchet) lever, the parking brake operating lever or any other springs you see.
4. Remove whatever else is connecting the two brake shoes. This usually includes the self-adjuster wheel, which has a slot at each end where the brake shoe sits. With the springs removed it should simply slide out from between the shoes. On some brake designs there might be a metal strut on the side of the brake opposite the self-adjuster, and with no spring tension to hold it in place this too should just slide out from between the shoes.
5. Remove the shoe hold-down pins. On small vehicles there is normally one hold-down pin for each shoe while larger vehicles may have two pins on each shoe. The pins typically pass through the backing plate and have a spring-and-retainer or a spring clip to hold the pin in place while pushing the brake shoe against the backing plate. For pins with spring clips, grip the pin and the clip with separate pliers and rotate them until the tabs on the end of the pin align with the notches in the clip and pull the clip off the end of the pin. For pins with retaining springs, grip and retaining washer and rotate it until the notches in the washer align with the tabs on the spring end and pull the washer and retaining spring off the pin. For either arrangement, be careful because the spring tension will release suddenly when the retainer notches align with the pin tabs. Keep a firm grip on everything to prevent the small parts from flying away.
With the retainers removed the hold-down pins can be pushed out through the backing plate. This will release the front brake shoe, which can now be removed, however the rear brake shoe will still be connected to the parking brake cable.
6. Free the rear shoe by disconnecting the parking brake cable. On some simple designs the cable will have a swaged fitting on the end that is held in a clevis at the end of the operating lever. Other designs will have a retaining clip that can be removed with pliers and a screw driver. With the parking brake cable disconnected the rear shoe can be removed.
7. Disconnect any levers that are attached to the brake shoes. These are normally held to the shoes with a pin and retaining clip arrangement, and the retaining clip can be removed with pliers or a screw driver to allow the lever to be pulled off the shoe.
8. Measure the thickness of the brake shoe linings with a finely graduated ruler and compare to the manufacturer's recommended minimum. This information can be found in the appropriate shop manual or aftermarket equivalent repair manual, or you can ask at an auto parts store. If the lining thickness is less than the allowable minimum, or if the linings are damaged or show uneven wear, replace the shoes.
9. Verify that the drum is round and is not worn out. Measure the inside diameter of the brake drum in several directions using a drum micrometer. The diameter should be equal in all directions. The interior surface of the drum should not have any deep grooves, pits or cracks. Compare the drum diameter to the manufacturer's recommended maximum diameter. This information can be found in the appropriate shop manual or aftermarket equivalent repair manual. If no manual is available, the maximum allowable drum diameter is normally stamped into the metal of the outside of the drum. If the measured diameter exceeds the allowable maximum then the drum is worn out and must be replaced.
10. Clean the backing plate with brake cleaning fluid. Unscrew the parts of the adjuster wheel and remove the pushrod end. Clean the parts with brake cleaning fluid and lubricate the threads and the pushrod female section with high temperature brake grease before reassembling the parts again. Also apply brake grease to the points where the brake shoes contact the backing plate, and the points where the brake shoes pivot on the hold down pins. Lubricate the points where the cylinder contacts the shoes, and the operating and adjusting levers pivot points. Be careful not to get grease on the drum or lining surfaces.
Tags: parking brake, backing plate, brake shoes, brake shoe, brake cable
