Brake Rotor Thickness Measurement
Brake Rotor Thickness Measurement
Caution: Refer to Brake Dust Caution in Cautions and Notices.
1. If the inboard friction surface of the brake rotor is not accessible, reposition and support the caliper with the brake pads. Refer to Brake Pads Replacement - Front (J55) or Brake Pads Replacement - Front (without J55) and/or Brake Pads Replacement - Rear (J55) or Brake Pads Replacement - Rear (without J55).
2. Clean the friction surfaces of the brake rotor with denatured alcohol, or an equivalent approved brake cleaner.
3. Using a micrometer calibrated in thousandths-of-a-millimeter, or ten-thousandths-of-an-inch, measure and record the thickness of the brake rotor at four 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 (1/2 in), for each measurement.
4. Compare the lowest thickness measurement recorded to the following specifications:
Specification
^ Front brake rotor minimum allowable thickness after refinishing 31.08 mm (1.224 in).
^ Front brake rotor (J55) minimum allowable thickness after refinishing 36.5 mm (1.437 in).
^ Rear brake rotor minimum allowable thickness after refinishing 10.25 mm (0.404 in).
^ Rear brake rotor (J55) minimum allowable thickness after refinishing 18.5 mm (0.728 in).
^ Front brake rotor discard thickness 30.7 mm (1.209 in).
^ Front brake rotor (J55) discard thickness 36.4 mm (1.433 in).
^ Rear brake rotor discard thickness 9.0 mm (0.354 in).
^ Rear brake rotor (J55) discard thickness 18.4 mm (0.724 in).
5. If the lowest thickness measurement of the brake rotor is above the minimum allowable thickness after refinishing specification, the rotor may be able to be refinished, depending upon use and wear conditions which may be present.
6. If the lowest thickness measurement of the brake rotor is at or below the minimum allowable thickness after refinishing specification, the or may not be refinished.
7. If the lowest thickness measurement of the brake rotor is at or below the discard thickness specification, the rotor requires replacement.
Brake Rotor Thickness Variation Measurement
Caution: Refer to Brake Dust Caution in Cautions and Notices.
Important: 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 caliper with the brake pads. Refer to Brake Pads Replacement - Front (J55) or Brake Pads Replacement - Front (without J55) and/or Brake Pads Replacement - Rear (J55) or Brake Pads Replacement - Rear (without J55).
2. Clean the friction surfaces of the brake rotor with denatured alcohol, or an equivalent approved brake cleaner.
3. Using a micrometer calibrated in thousandths-of-a-millimeter, or ten-thousandths-of-an-inch, measure and recor the thickness of the brake rotor at four 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 (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.
5. Compare the thickness variation measurement to the following specification:
Specification
Brake rotor maximum allowable thickness variation: 0.025 mm (0.001 in)
Important: 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.
