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Brake Disc Thickness Variation Measurement

Warning: Refer to Brake Dust Warning in the Preface section.

Note: Any disc brake rotor that exhibits thickness variation exceeding the maximum acceptable level must be refinished or replaced. Thickness variation exceeding the maximum acceptable level can cause brake pulsation.

1. If the inboard friction surface of the brake rotor is not accessible, reposition and support the calliper with the brake pads. Refer to Front Disc Brake Pads Replacement and/or Rear Disc Brake Pads Replacement , if equipped.
2. Clean the friction surfaces of the brake rotor with methylated spirit, or an equivalent approved brake cleaner.



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

Ensure 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 rotor, about 13 mm (0.5 in), for each measurement.

4. Calculate the difference between the highest and lowest thickness measurements recorded to obtain the amount of thickness variation.
5. Compare the thickness variation measurement to the disc brake component specifications.

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

6. If the brake rotor thickness variation measurement exceeds the specification, the rotor requires refinishing or replacement. Refer to Front Brake Disc Replacement , Rear Brake Rotor Replacement or Brake Disc Refinishing .