Tools Required

J 8001 Dial Indicator, or equivalent

1. Clean the braking surface of the brake drum with GM Brakes Parts Cleaner, GM P/N 12346139, or an equivalent brake cleaner.
2. Inspect the braking surface of the brake drum for the following braking surface conditions:

•	Heavy rust and/or pitting

•	Light surface rust can be removed with an abrasive disc; heavy surface rust and/or pitting must be removed by refinishing the drum.

•	Cracks and/or heat spots

•	Excessive bluing discoloration

•	Missing balance weights

3. If the braking surface of the brake drum exhibits one or more of the braking surface conditions, replace the brake drum. Refer to Brake Drum Replacement .



4. Using a brake drum micrometer calibrated in thousands of an inch, measure and record any grooves present on the drum braking surface.
5. Compare the groove depth to the following specification:

Specification
The maximum groove depth is 1.00 mm (0.039 in).

6. If the groove depth exceeds the specification, or if an excessive amount of scoring is present, refinish or replace the brake drum.
7. Mount the brake drum on a brake lathe.
8. Mount a dial indicator, J 8001 or equivalent, and position the indicator button so it contacts the braking surface of the brake drum at a 90 degree angle, approximately 19 mm (0.75 in) from the drum's outer edge.
9. Measure and record the radial runout of the brake drum.

9.1.	Rotate the drum until the lowest reading is displayed on the indicator dial, then zero the dial.

9.2.	Rotate the drum until the highest reading is displayed on the dial.

10. Compare the radial runout of the brake drum to the following specification:

Specification
The maximum radial runout of the brake drum is 0.04 mm (0.002 in).

11. If the radial runout exceeds the specification, refinish or replace the drum.