Brake Drum Surface & Wear Inspection
- Clean the braking surface of the brake drum with Brakes Parts Cleaner (GM 12346139), or equivalent brake cleaner.
- 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.
- If the braking surface of the brake drum exhibits one or more of the braking surface conditions, replace the brake drum. See BRAKE DRUMS
under REMOVAL & INSTALLATION.
- Using the brake drum micrometer calibrator in thousands on an inch, measure and record any grooves present on the drum braking surface. Groove depth should be no more than 0.039" (1.00 mm). If the groove depth exceeds the specifications, or if an excessive amount of scoring is present, refinish or replace the brake drum.
- Mount the brake drum on a brake lathe. Mount a Dial Indicator (J-8001) or equivalent, and position the indicator button so it contacts the braking surface of the brake drum from at a 90 degree angle, approximately 0.75" (19 mm) from the drum's outer edge.
- Measure and record the radial runout of the brake drum. Rotate the drum until the lowest reading is displayed on the indicator dial, then zero the dial. Rotate the drum until the highest reading is displayed on the dial.
- The maximum radial runout of the brake drum should be, 0.002" (0.04 mm). If the radial runout exceeds the specifications, refinish or replace the drum.