Brake Rotor/Disc: Testing and Inspection
Diagnostic Information and Procedures
Brake Rotor Tolerance
Manufacturers closely hold brake rotor tolerances. These tolerances include flatness of the braking surfaces, parallelism, and lateral runout.
Maintaining the close tolerance on the shape of the braking surface prevents brake roughness or pulsation. The surface finish must be maintained at 60 Ra roughness or less.
Control the braking surface finish in order to avoid the following conditions:
- Hard pedal application.
- Excessive brake fade.
- Brake and steering pulls.
- Erratic brake performance.
Controlled braking surface finish can prolong the life of the brake lining. Light scoring of the rotor braking surface not exceeding 1.5 mm (0.06 in) in depth is normal and will not damage the brake operation.
Brake Rotor Thickness Variation Check
Check for thickness variation by measuring the rotor thickness at four or more points around the circumference of the rotor (1-4). 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 front rotor that varies in thickness by more than 0.010 mm (0.0003 in) or, a rear rotor that varies in thickness by more than 0.013 mm (0.0005 in) can cause brake pedal pulsation and/or vehicle vibration during brake applications. Refinish to specifications or replace a rotor that does not meet these specifications.
Brake Rotor Lateral Runout Check (Front)
Check the rotor for lateral runout using the following procedure:
Tools Required
- J8001 Dial Indicator Set
1. Remove the tire and the wheel.
2. Tighten the wheel nuts so that the rotor is tight against the hub (JC1 system only).
3. Adjust the wheel bearings in order to eliminate excessive freeplay (RWD pickups only).
4. Clean the rotor surface.
5. Install the J8001 Dial Indicator so that the dial indicator button contacts the rotor surface about 25 mm (1.0 in) from the outer edge.
6. Set the dial indicator to zero.
7. Turn the rotor one complete revolution and observe the lateral runout on the dial indicator. The total indicator runout (TIR) should not exceed 0.08 mm (0.003 in).
8. If lateral runout is not within specifications refinish or replace the rotor (RWD pickups only).
9. In some cases, excessive lateral runout can be rectified by indexing the rotor. Move the rotor one or two wheel bolt positions from the original position (JC1 system only).
10. If the lateral runout still exceeds 0.08 mm (0.003 in), check the hub for excessive lateral runout, or looseness (JC1 system only).
1. Remove the brake rotor.
2. Reposition the J 8001 Dial Indicator so that the button contacts the surface of the hub.
3. Set the dial indicator to zero.
4. Rotate the hub one complete revolution.
5. Note the lateral runout.
6. If the hub lateral runout exceeds , replace the hub.
7. If the hub lateral runout is within specifications, refinish or replace the rotor.
Brake Rotor Lateral Runout Check (Rear)
Check the rotor for lateral runout using the following procedure:
Tools Required
- J8001 Dial Indicator Set
1. Remove the tire and the wheel.
2. Tighten the wheel nuts so that the rotor is tight against the axle flange.
3. Clean the rotor surface.
4. Install the J 8001 Dial Indicator so that the dial indicator button contacts the rotor surface about 13 mm (0.5 in) from the outer edge.
5. Push in the rear axle while setting the dial indicator to zero.
6. While maintaining the inward pressure, turn the rotor one complete revolution.
7. Observe the lateral runout on the dial indicator. The total indicator runout (TIR) should not exceed 0.10 mm (0.004 in).
8. In some cases, excessive lateral runout can be rectified by indexing the rotor. Move the rotor one or two wheel bolt positions from the original position.
9. If the lateral runout still exceeds 0.10 mm (0.004 in),check the rear axle shaft flange for excessive lateral runout, or looseness.
1. Remove the brake rotor.
2. Reposition the J 8001 Dial Indicator so that the button contacts the surface of the axle shaft flange.
3. Push the axle shaft flange inward while turning the axle shaft flange one full revolution.
4. Continue pushing in the axle shaft flange while setting the dial indicator to zero.
5. While maintaining the inward pressure, rotate the axle shaft flange one complete revolution.
6. Note the lateral runout.
7. If the axle shaft flange lateral runout exceeds 0.05 mm(0.002 in), replace the rear axle shaft.
8. If the axle shaft flange lateral runout is within specifications, refinish or replace the rotor.