GM Full Size Vans 1967-1986 Repair Guide

Brake Drum



See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Slide the brake drum off of the wheel studs on the axle shaft

Do not blow the brake dust out of the drums with compressed air. It may contain asbestos, which has been found to be a cancer producing agent.

Drums 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. To remove the drums from full floating rear axles, follow Steps 1-11 of the Axle Shaft removal and installation procedure in Drive Train . Full floating rear axles can readily be identified by the bearing housing protruding through the center of the wheel.

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.


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

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 is removing metal from the entire inner surface of the drum on a lathe in order to level the surface. Automotive machine shops and some large 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 more than 0.060 in. (1.524mm).

Your state inspection law may disagree with this specification.

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. (0.1524mm) out-of-round will result in an inaccurate brake adjustment and other problems, and should be refinished or replaced.

Make all measurements at right angles to each other and at the open and closed edges of the drum machined surface.