Tools Required:

J 8001  Dial Indicator, or equivalent. See Special Tools and Equipment .

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 pitting.

   • 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.
Fig 1: Measuring Brake Drum
Courtesy of GENERAL MOTORS CORP.
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.
   1. Install the brake drum on a brake lathe.
   2. Install a dial indicator, J 8001  or equivalent. See Special Tools and Equipment . 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.
   3. Rotate the drum until the indicator dial displays the lowest reading.
   4. Set the dial to zero.
   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 (0.002 in).

9. If the radial runout measurement exceeds the specification, refinish or replace the brake drum.