Rotor Refinishing

ROTOR REFINISHING

Rotor refinishing should only be performed when rotor thickness variation (non-parallelism) is present or when the rotor surface has scoring grooves deeper than .015 inches. Replacement rotors taken from stock should be mounted and checked for lateral run out; and if run out exists, then the rotor must be refinished on the vehicle.

When rotors are refinished, a correct surface finish is important for satisfactory braking. Following a light finish-cutting operation of between .001 and .002 inches, correct surface should be obtained by rubbing with 120 grit emery cloth. Surface finish may be checked by running a fingernail over the surface of a new rotor from stock or one from a known good vehicle. For best results, cutting equipment should be maintained in correct working condition. If an acceptable finish surface cannot be obtained, contact the equipment manufacturer for assistance.
On-Vehicle Rotor Finishing:

The recommended procedure for refinishing brake rotors is through the use of on-vehicle rotor turning equipment (Kent-Moore J-37704). This method is particularly effective because it can compensate for stacked tolerances that cause rotor/bearing system run out, and help prevent a return of the condition. Full set up and operating instructions are provided with the equipment. Contact Kent-Moore for ordering information.

We believe this source and their equipment to be reliable. There may be additional manufacturers of such equipment. General Motors does not endorse, indicate any preference for, or assume any responsibility for product or equipment from these firms or for any such items which may be available from other sources.

FIGURE 1 - HOLE WHEEL NUT TIGHTENING SEQUENCE:

Lateral Run out Check:

A lateral run out check is an integral part of the on-car refinishing procedure. If off-vehicle rotor refinishing is used, the following lateral run out check should be performed:

1. Remove wheel, invert wheel nuts, and reinstall them on the studs. Tighten nuts to 20 ft.lbs. following the tightening sequence shown in Figure 1.

2. Fasten a dial indicator to the caliper so that the indicator button contacts the rotor approximately 13 mm (0.500") from the outer edge.

3. Zero the dial indicator needle.

4. Rotate the rotor one complete revolution while observing run out indicated on the dial. Total Indicated Run out (TIR) should not exceed 0.08 mm (0.003").

On front-wheel-drive vehicles, lateral rotor run out due to stacked tolerances can often be reduced by rotating (indexing) the rotor one or two bolt holes in relation to the hub. If excessive run out cannot be corrected by indexing the rotor, check the hub and bearing assembly for looseness.

NOTICE: Whenever the brake rotor has been separated from the wheel bearing flange, clean any rust or foreign material from the mating surfaces of the wheel bearing flange and rotor. Failure to do this may result in increased lateral run out of the rotor and brake pulsation.

5. If lateral rotor run out exceeds the amount specified in step 4, refinish the rotor on the vehicle.

Rotor Thickness Variation Check:

Variations in rotor thickness can be checked by measuring the thickness of the rotor at four or more points around the surface of the rotor. Use a micrometer calibrated in one-tenth increments per .001". All measuring points must be the same distance in from the edge of the rotor.

A rotor that varies in thickness by more than 0.013 mm (0.0005") can cause pedal pulsation and/or front-end vibration during brake applications. Rotors with 0.013 mm or higher thickness variations should be refinished or replaced as necessary.