Chevrolet Sonic Repair Manual: Brake Rotor Thickness Variation Measurement

1. If the inboard friction surface of the brake rotor is not accessible, reposition and support the caliper with the brake pads. Refer to Front Disc Brake Pads Replacement.
2. Clean the friction surfaces of the brake rotor with denatured alcohol, or an equivalent approved brake cleaner.


3. Using a micrometer (1) calibrated in thousandths-of-a-millimeter, or ten-thousandths-of-an-inch, measure and record the thickness of the brake rotor at 4 or more points, evenly spaced around the brake rotor.

   Make sure that the measurements are only taken within the friction surfaces and that the micrometer is positioned the same distance from the outer edge of the brake rotor, about 13 mm (1/2 in), for each measurement.

4. Calculate the difference between the highest and lowest thickness measurements recorded to obtain the amount of thickness variation.

Note:

Whenever a brake rotor is refinished or replaced, the assembled lateral runout (LRO) of the brake rotor must be measured to make sure optimum performance of the disc brakes.

5. Compare the thickness variation measurement to the following specification: Specification

   
   

   • J93, J94: 0.02 mm (0.0008 in)

   • JPW, J97: 0.02 mm (0.0008 in)

6. If the brake rotor thickness variation measurement exceeds the specification, the brake rotor requires refinishing or replacement.

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