Brake Rotor/Disc: Testing and Inspection

1. Check for free play in the wheel bearing by grasping opposite sides of the wheel and rocking it to and fro.
- Rotate the wheel through 90 degrees and repeat.
- Change the wheel bearing if free play is detected.
2. Remove the wheel and brake caliper from the wheels causing vibration.
- Hang up the caliper with a cable tie.
3. Tighten the brake disc.
- Install 4 washers, part No. (10) 80 73 124, under the wheel bolts.
- The washers protect the wheel bolt's taper and prevent the bolt from touching the bearing housing.
4. Mount a brake disc measuring tool, part No. (116) 89 96 639, on the lower retaining lug for the brake caliper and fit the dial gauges, part No. (116) 78 40 622, on the measuring tool.
- Adjust the measuring tool so that the tips of the dial gauges are r=130 mm from the wheel center (front discs) and r= 120 from the wheel center (rear discs).





5. Rotate the brake disc while observing the outboard dial gauge.
- Zero both gauges when the negative reading obtained on the outboard one is at maximum.
6. Rotate the disc and read the gauges.
- Note the runout (A) and variation in thickness (B).
- If the runout exceeds the tolerance limits, check the wheel hub.
- If the hub is OK then the brake disc is defective and should be changed or reground.
- For measurement details, see "Specifications".
- If variation in thickness exceeds the maximum permissible limit, the disc should be changed.
7. Remove the dial gauges, brake disc measuring tool and wheel bolts with washers.
8. Install the brake caliper.
9. Install the wheels and tighten the wheel bolts, using a torque wrench.
- Tighten to: 120 Nm (89 ft lb)
10. When the measurements have been completed, lower the car and depress the brake pedal to press out the brake pads.