GM Full-Size Trucks 1980-1987 Repair Guide

Brake Drums



See Figures 1 and 2

Drums on all models can be removed by raising the vehicle, removing the wheel lugs and the tire, and pulling the drum from the brake assembly. If the brake drums have been scored from worn linings, the brake adjuster must be backed off so that the brake shoes will retract from the drum. Some drums are retained by two screws to the hub, and can be removed after removing the screws.

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Fig. Fig. 1: If difficulty is encountered removing the brake drum, it may be loosened by lightly tapping with a rubber mallet

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Fig. Fig. 2: Pull the brake drum from the hub of the axle shaft

The adjuster can be backed off by inserting a brake adjusting tool through the access hole provided. In some cases the access hole is provided in the brake drum. A metal cover plate is over the hole. This may be removed by using a hammer and chisel.

Make sure all metal particles are removed from the brake drum before reassembly.

To install, reverse the removal procedure.

Brake shoes contain asbestos, which has been determined to be a cancer causing agent. Never clean the brake surface with compressed air! Avoid inhaling any dust from any brake surface! When cleaning brake surfaces, use a commercially available brake cleaning fluid.


See Figure 3

When a drum is removed, it should be inspected for cracks, scores, or other imperfections. These must be corrected before the drum is replaced.

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Fig. Fig. 3: Make sure the drum is smooth and free of cracks, scores or other damage

If the drum is found to be cracked, replace it. Do not attempt to service a cracked drum.

Minor drum score marks can be removed with fine emery cloth. Heavy score marks must be removed by "turning" the drum. This procedure removes metal from the entire inner surface of the drum in order to level the surface. Automotive machine shops and some parts stores are equipped to perform this operation.

If the drum is not scored, it should be polished with fine emery cloth before replacement. If the drum is resurfaced, it should not be enlarged past 0.060 in. of the original diameter.

All brake drums have a maximum diameter number cast into their outer surface. This number is a maximum wear diameter and not a refinish diameter. Do not refinish a brake drum that will not meet specifications after refinishing.

It is advisable, while the drums are off, to check them for out-of-round. An inside micrometer is necessary for an exact measurement; therefore unless this tool is available, the drums should be taken to a machine shop to be checked. Any drum which is more than 0.006 in. out-of-round will result in an inaccurate brake adjustment and should be refinished or replaced.

If the micrometer is available, make all measurements at right angles to each other and at the open and closed edges of the drum machined surface.

Check the drum with a micrometer in the following manner:

  1. Position the drum on a level surface.
  3. Insert the micrometer with its adapter bars if necessary.
  5. Obtain a reading on the micrometer at the point of maximum contact. Record this.
  7. Rotate the micrometer 45 degrees and take a similar reading. The two readings must not vary more than 0.006 in..