Tools Required

J 26900-1  Combimike Micrometer. See Special Tools and Equipment .

1. Reposition and support the caliper and the brake pads. Refer to Brake Pads Replacement - Front  or to Brake Pads Replacement - Rear  as applicable.
2. Clean the friction surfaces of the brake rotor with denatured alcohol or an equivalent brake cleaner.
Fig 1: Measuring Brake Rotor Thickness
Courtesy of GENERAL MOTORS CORP.
3. Use a J 26900-1  , or the equivalent micrometer, in order to measure the thickness of the brake rotor. See Special Tools and Equipment . Measure the thickness of the rotor at 4 or more points equally spaced around the rotor. Position the J 26900-1  , or the equivalent, at the same distance from the outside edge of the rotor, in the brake pad lining contact area. See Special Tools and Equipment .
4. Calculate the difference between the highest and lowest thickness measurements in order to obtain the amount of thickness variation.
5. Compare the thickness variation measurement to the following specification:

   Specification: 

   • The maximum thickness variation of the front rotors is 0.025 mm (0.001 in).
   • The maximum thickness variation of the rear rotors is 0.025 mm (0.001 in).

IMPORTANT: Brake rotor thickness variation greater than the specification can cause brake pulsation.
6. If the brake rotor thickness variation measurement exceeds the specification, refinish or replace the rotor. In order to refinish the rotor, refer to Brake Rotor Refinishing . In order to replace the rotor, refer to Brake Rotor Replacement - Front  or to Brake Rotor Replacement - Rear  as applicable.
7. If you refinish or replace the rotor, measure the assembled lateral runout (LRO) of the rotor in order to verify the performance of the disc brake system. Refer to Brake Rotor Assembled Lateral Runout (LRO) Measurement .