Brake Rotor Wear Tolerance Test Thickness Variation Check
Check thickness variation by measuring the rotor thickness at four or more points around the circumference of the rotor. Use a micrometer calibrated in ten-thousandths of an inch. Make all measurements at the same distance in from the edge of the rotor.
A rotor that varies in thickness by more than 0.025 mm (0.001 in) can cause pedal pulsation and/or front end vibration during brake applications. A rotor that does not meet these specifications should be refinished to specifications or replaced.
Brake Rotor Wear Tolerance Test Lateral Runout Check
The best way to check lateral runout is with the wheels still installed on the vehicle. This gives a much more accurate reading of the Total Indicated Runout under real braking conditions. If equipment is not available to perform the check with the wheels installed, the next best reading can be made with the wheels removed but the caliper still installed.
Important: If the wheel must be removed, re-install the wheel nuts to retain the rotor. Tighten the wheel nuts to the correct torque specification following the proper wheel nut tightening sequence.
- Clean the rotor surface.
- Fasten a dial indicator to the steering knuckle so that the indicator button contacts the rotor surface about 13 mm (0.5 in) from the outer edge.
- Set the dial indicator to zero.
- Turn the wheel one complete revolution and observe the runout indicated on the dial. The Total Indicated Runout must not exceed 0.008 mm (0.003 in).
- If lateral runout exceeds the amount specified in Step 4, refinish or replace the rotor.
In some cases excessive lateral runout of the rotor can be improved by indexing the rotor on the hub one or two bolt positions from the original position. If the lateral runout cannot be corrected by indexing the rotor, check the hub and bearing assembly for excessive lateral runout or looseness. If the hub and bearing assembly lateral runout exceeds 0.06 mm (0.002 in) then replace the hub and bearing assembly. If lateral runout is within specifications then refinish or replace the rotor as necessary.
Important: Whenever the brake rotor has been separated from the wheel bearing flange, clean any rust or foreign material from the mating surface of the wheel bearing flange and rotor. Failure to do this may result in increased lateral runout of the rotor and brake pulsation.
Brake Rotor Wear Tolerance Test Tolerance
In manufacturing the brake rotor, tolerances of the braking surfaces for flatness, parallelism and lateral runout are closely maintained. The maintenance of close tolerances on the shape of the braking surfaces is necessary to prevent brake roughness or pulsation.
In addition to these tolerances, the surface finish must be maintained to a specified range, 60 Ra roughness or less. A new rotor falls into this surface finish range, as will a rotor that is refinished exactly as directed in Refinishing the Brake Rotors. The control of the braking surface finish is necessary to avoid problems of hard pedal apply, excessive brake fade, pulls and erratic performance. In addition, control of the surface finish can improve brake pad life.
Light scoring of the rotor surfaces not exceeding 1.5 mm (0.060 in) in depth is not detrimental to brake operation, and may result from normal use.
