Rotor Inspection - Rear Disc Brake

Brake rotors are manufactured with close tolerances for thickness variation, flatness, and lateral runout. However, pits and grooves are created in rotors during usage. The lack of uniformity of braking surfaces of rotor can cause inadequate braking and a pulsating pedal during braking. The surface finish of rotor is also important because an unsuitable surface finish can cause pulling and rapid wear of brake shoe lining.

If a rotor does not meet specifications, it should be refinished to specification or replaced. Refinishing of rotor should only be done with precision equipment. 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 from edge of rotor. A rotor that varies by more than .10 mm (.004") can cause pedal pulsations and/or front end vibration during braking. Thickness can be measured with a commercially available micrometer.

If a rotor does not meet specifications, it should be refinished to specification or replaced. Refinishing of rotor should only be done with precision equipment. 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 from edge of rotor. A rotor that varies by more than .10 mm (.004") can cause pedal pulsations and/or front end vibration during braking. Thickness can be measured with a commercially available micrometer.

Light scoring of rotor surfaces is acceptable if it does not exceed .40 mm (.016") in depth. Scoring measurements can be made with a commercially available brake micrometer. Lateral runout cannot exceed .005 mm (.0005"). If lateral runout exceeds specification, make sure there is no dirt between rotor and hub and that hub-to-rotor contact surfaces are smooth and free from burrs.

Use a commercially available dial indicator to check lateral runout according to following procedure:

1. Position transaxle in NEUTRAL and raise vehicle. To preserve wheel balance, mark relative positions of wheel and hub, and remove front wheel. Fasten brake rotor to wheel hub with two wheel bolts. Fasten a dial indicator to brake caliper.
2. Place gauge tip approximately 234 mm (9.2") from center of rotor hole, perpendicular to disc and under slight preload. Observe gauge while rotating rotor. After measuring is completed, remove dial indicator and wheel bolts.
3. If necessary, refinish rotor with precision equipment. Measure runout again after refinishing. If runout exceeds .005 mm (.0005") after refinishing, rotor should be replaced. Align marks that were made before wheel was removed and install front wheel. Lower vehicle.