Rotor Inspection - Front Disc Brake

Thickness variation can be checked by measuring thickness of rotor at four or more points around circumference of rotor. All measurements must be made at same distance in from edge of rotor. A rotor that varies by more than .005 mm (.0005") can cause pedal pulsations and/or front end vibration during brake applications.

A rotor that does not meet these specifications should be refinished to specifications or replaced. During manufacturing, brake rotor and tolerances of braking surface regarding flatness, thickness variation, and lateral runout are held very close. The maintenance of close tolerances on shape of braking surfaces is necessary to prevent brake roughness.

In addition to these tolerances, surface finish must be held to a specified range. The control of braking surface finish is necessary to avoid pulls and erratic performance and to extend lining life. Using a commercially available dial indicator, check lateral runout as follows:

1. Position transaxle in NEUTRAL. Remove rotor. Fasten brake rotor to wheel hub with two wheel bolts. Fasten a dial indicator to brake caliper. See Fig 1.
2. Set gauge probe tip to approximately 10 mm (0.39") from outer edge of brake rotor, perpendicular to disc and under slight preload. Remove dial indicator and wheel bolts connecting rotor to hub.
   NOTE: Since accurate control of rotor tolerances is necessary for proper performance of disc brakes, refinishing of rotor should be done only with precision equipment.
3. Refinish rotor, if required, with precision equipment. Discard rotor if it fails to meet above specifications after refinishing. Install rotor.

Fig 1: Measuring Brake Disc Runout

Courtesy of DAEWOO MOTOR AMERICA, INC.