Brake Rotor Surface and Wear Inspection

Tools Required 

J 8001  Dial Indicator set or equivalent. See Special Tools .

1. Raise and support the vehicle.
2. Remove the tire and wheel assemblies. Refer to TIRE AND WHEEL REMOVAL AND INSTALLATION in Tires and Wheels.
3. Clean the braking/friction surfaces of the brake rotor with denatured alcohol or an equivalent approved brake cleaner.
4. Inspect the braking surfaces of the brake rotor for the following braking surface conditions:
   • Heavy rust and/or pitting
   • Cracks and/or heat spots
   • Excessive blueing discoloration
5. Light surface rust can be removed with an abrasive disc. If the braking surfaces of the brake rotor exhibits one or more of the remaining conditions then the brake rotor requires refinishing or replacement.
Fig 1: Measuring Brake Rotor Thickness
Courtesy of GENERAL MOTORS CORP.
6. Using a calibrated micrometer measure and record the thickness variation of the brake rotor at 4 or more points around the rotor.

   Ensure that the measurements are only taken within the brake pad lining contact area and that the micrometer is positioned the same distance from the outside edge of the rotor for each measurement.

7. Compare the thickness variation recorded to the following specification:

   Specification:  Brake rotor maximum allowable thickness variation 0.025 mm (0.001 in).

8. If the brake rotor thickness variation exceeds the specification, the brake rotor requires refinishing. Refer to Brake Rotor Refinishing ,Brake Rotor Replacement - Front , or Brake Rotor Replacement - Rear .
9. Using the micrometer measure and record any grooves present on the rotor braking surface.
10. Compare the groove/scoring depth recorded to the following specification:

    Specification:  Brake rotor maximum allowable scoring 1.50 mm (0.059 in).

11. If the brake rotor scoring depth exceeds the specification or if an excessive amount of scoring is present, the brake rotor requires refinishing. Refer to Brake Rotor Refinishing , Brake Rotor Replacement - Front  or Brake Rotor Replacement - Rear .
Fig 2: Checking Brake Rotor Runout
Courtesy of GENERAL MOTORS CORP.
IMPORTANT: Ensure the wheel bearings are properly adjusted before proceeding with the following steps.
12. Mount a dial indicator, J 8001  or equivalent, and position the indicator button so it contacts the brake rotor at a 90 degree angle, approximately 13 mm (0.5 in) from the rotor's outer edge. See Special Tools .
13. Measure and record the lateral runout of the brake rotor.
    1. Rotate the rotor until the lowest reading is displayed on the indicator dial, then zero the dial.
    2. Rotate the rotor until the highest reading is displayed on the dial.
14. Compare the lateral runout reading to the following specification:

    Specification:  Brake rotor maximum allowable lateral runout 0.05 mm (0.002 in).

15. If the brake rotor lateral runout exceeds the specification, the brake rotor requires refinishing. Refer to Brake Rotor Refinishing , Brake Rotor Replacement - Front , orBrake Rotor Replacement - Rear