Brake Drum Surface and Wear Inspection

Brake Drum Surface and Wear Inspection

Tools Required:
J 8001 Dial Indicator, or equivalent

1. Clean the brake shoe lining contact surface of the brake drum with GM Brake 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
Use an abrasive disc in order to remove light surface rust
Refinish the drum in order to remove heavy surface rust and/or pining
^ Cracks and/or heat spots
^ Excessive blueing discoloration
^ Missing balance weights
3. If the braking surface of the brake drum exhibits one or more of the braking surface conditions, refinish or replace the drum.
4. Using a brake drum micrometer calibrated in thousands of an inch, measure 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 drum.
7. Perform the following steps in order to measure the radial runout of the brake drum.
7.1. Install the brake drum on a brake lathe.
7.2. Install a dial indicator, J 8001 or equivalent. 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.
7.3. Rotate the drum until the indicator dial displays the lowest reading.
7.4. Set the dial to zero.
7.5. Rotate the drum until the indicator dial displays the highest reading.
8. 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 (0.00016 in).
9. If the radial runout measurement exceeds the specification, refinish or replace the brake drum.