Front Disc Brakes

Rotor Tolerance and Surface Finish
During the manufacturing of the brake rotor, tolerances of the braking surfaces for flatness, parallelism, and lateral runout are closely held. 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 held to a specified range of 60 Ra roughness or less. The control of the braking surface finish is necessary to avoid problems of hard pedal application, excessive brake fade, brake and steering pulls, and erratic performance. In addition, control of the surface finish can improve lining life. Light scoring of the rotor surfaces not exceeding 1.5 mm (0.06 in) in depth is normal and not detrimental to brake operation.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-thousands 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 0.009 mm (0.0003 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.

Checking For Lateral Runout:

Lateral Runout Check
1. Clean rotor surface.
2. Tighten the wheel bearings to eliminate all free play.
3. Fasten a dial indicator to the steering knuckle so the indicator button contacts the rotor surface about 25 mm (1.0 in) from the outer edge.
4. Set the dial indicator to zero.
5. Turn the rotor one complete revolution and observe the Runout indicated on the dial.
6. The total indicated Runout (T.I.R.) must not exceed 0.08 mm (0.003 in).
7. If lateral runout is not within specifications, refinish or replace the rotor as necessary.
8. Adjust the wheel bearings.