How to Repair a Drum Brake System

Repairing drum brakes is not difficult when you know how.

To the inexperienced mechanic, working on a drum brake can seem like trying to diffuse a bomb. The apparent complexity of drum brakes can be baffling and intimidating. But as the saying goes, it is like trying to eat an elephant. If the task is broken down into bite-sized pieces then each piece is really not so difficult. With a little patience, perseverance, and knowledge just about anyone who can hold a wrench and squeeze a pair of pliers can also perform basic drum brake repairs.

Things You'll Need

• Wheel blocks
• Lug nut wrench
• Jack
• Safety stands
• Wrenches
• Mallet
• Screwdrivers
• Pliers
• Finely graduated ruler
• Brake drum micrometer
• Brake grease
• Brake cleaning fluid
• Catch pan
• Rags
• Wire brush

Instructions

1. Park the automobile on a firm, level surface. Block the front wheels to prevent the car from rolling. Be sure that the emergency brake is completely released. Put automatic transmissions in park and shift manual transmissions into first or reverse gear. Partly undo the wheel lug nuts on both rear wheels about one turn each. Jack up the rear of the automobile and set it securely on safety stands. Finish removing the lug nuts and pull both rear wheels off. One trick to simplify drum brake service is to remove the drums on both wheels so the assembled brake can serve as a visual guide when working on the other brake.

2. Remove the drums on both rear wheels. On some automobiles the drum will pull right off the hub. On others the drum may be held to the hub by retaining screws or bolts. If so, remove the retaining fasteners before pulling the drum off. On some vehicles the drum might be secured by a large hub nut. To remove the hub nut, first pry off the grease cap. If a lock nut or cotter pin is present, remove it. Remove the hub nut and pull the drum off the hub. The hub bearing will come with the drum, so as soon as the drum is off the spindle, remove the bearing and set it where it will not get dirty.

3. Free a seized drum by tapping it firmly around the outer shoulder with a rubber or plastic mallet. Sometimes, because of weak brake springs, an over extended adjuster or a stuck emergency brake, the shoes could be resting against the drum and preventing its removal. Look for a hole on backing plate with a rubber cover. Open the cover, reach inside with a small screwdriver and rotate the adjuster to release tension on the brake shoes. If the parking brake is stuck, find the parking brake cable tensioner bolt and loosen it. On larger vehicles the bolt is often under the car on the driver's side while in smaller vehicles it is typically at the base of the hand brake lever inside the passenger compartment.

4. Remove the brake springs. Drum brake springs are hooked at both ends and are removed by gripping one end of the spring with pliers and pulling to unhook it. With the spring tension relieved it is easy to unhook the other end. First remove the large return springs that connect the front and rear brake shoes. If these are very difficult to remove, rotate the self-adjuster mechanism to relieve some of the tension on the shoes. Next remove the smaller springs for the adjuster mechanism lever, the parking brake operating lever or any other springs that are present. It is helpful to draw a circle about 14 inches diameter on a piece of paper and place this on the ground nearby. You can then lay the removed parts on the circle in a position similar to their arrangement in the brake to help you remember how to put everything back together again. Examine each spring and replace any that are damaged or heavily corroded.

5. Remove anything else connecting the two brake shoes. This usually includes the adjuster mechanism, and perhaps a metal strut on the side of the brake opposite the adjuster. With no spring tension to hold these in place they should slide out from between the shoes.

6. Remove the shoe hold-down pins. Depending on the brake size there may be one or two pins on each shoe. The pins pass through the backing plate and have a spring-and-retainer or a spring clip to hold the brake shoe in place 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 pin end and pull the washer and retaining spring off the pin. For either arrangement, be careful because the spring tension could release suddenly. With the retainers removed the the front brake shoe is now free and can be removed.

7. Disconnect the parking brake cable from the rear brake shoe. The cable end is usually secured by a retaining clip that can be removed with pliers or a screw driver. Once the cable end is removed, pull the rear shoe off the backing plate.

8. Disconnect any levers that are attached to the brake shoes. These are usually fixed to the shoes with a pin and retaining clip arrangement. Remove any retaining clips using pliers or a screwdriver and pull the levers off the shoes.

9. Measure the thickness of the brake shoe linings using a finely graduated ruler and compare to the manufacturer's specified minimum. This information can be found in the appropriate shop manual or aftermarket equivalent repair manual, which are often available at the local public library. Alternatively, 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.

10. Measure the inside diameter of the brake drum in several directions using a drum micrometer. The drum is round if the diameter is the same in all directions. The interior surface of the drum should be free from 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, and is also normally stamped into the metal of the outside of the drum. If the drum is irreparably damaged, or if the measured diameter exceeds the allowable maximum, replace the drum. Minor damage to the drum can be repaired by having the drum machined at an auto parts store.

11. 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 brake grease before reassembling. 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.

12. Reassemble the brake by following steps in reverse order. Use the assembled brake as a guide. Repeat the procedure on the other brake.

13. Replace the wheels and lower the car. Start the engine and gently pump the brakes a few times to seat all the parts. Make a few careful stops in reverse to seat the brake adjusters. Test the brake operation before driving normally.

Tips & Warnings

• Brake grease is specifically designed for the high temperatures generated during braking. Do not use normal grease as it can easily melt at these temperatures.

• Take care not to inhale brake dust or brake cleaning fluid fumes. Work in a well ventilated area.

References

• 2 Car Pros: How to Replace Rear Brake Shoes and Drums?
• AA1 Car: Drum Brake Service
• For Dummies: How to Check Drum Brakes
• Everything Auto: Replacing Brake Shoes

Resources

• Family Car Parts: A Short Course on Brakes