Inspection
1. The brake disc gets circular scratches when braking due to the capture of dust and road sand. Excessive scratching not only creates brake squeal, but also shortens the life of the brake pads. However, slight damage to the surface of the disc, not exceeding 0.38 mm in depth, occurs during normal operation. It is not dangerous when braking. If the grooves are deep enough to catch the nail, then appropriate measures must be taken.
Differences on the left and right surfaces of the disc can lead to uneven braking.
2. The beating of the disc occurs when the disc moves from side to side, warping or deformation. Excessive wobble causes the brake pedal to vibrate or rattle. Place a dial indicator in the middle of the worn surface of the pad and turn the disc, observing the reading. If disc runout exceeds 0.10 mm, replace or regrind disc.
3. The parallelism of the disk is checked by measuring the thickness of the disk at different positions around the circumference of the disk. To check the disk for parallelism, put a mark on the disk and measure the thickness of the disk with a micrometer. Repeat this measurement eight times, moving around the circumference of the disc (each time approximately 45 degrees). If the measurements change by more than 0.015 mm, then replace the disc.
Regrinding
Brake discs can be restored if the following rules are observed:
- Nowhere should the disc be thinner than the minimum thickness. (The limits are specified in Specifications for Brakes in this Chapter). The difference between new disc thickness and the absolute limit is usually very small; if the disc has been used for several years, then it is already close to the limit, and regrinding will not be able to eliminate defects without exceeding the wear limits. It's always better to replace the drive.
- If the disc is being reground, then the procedure must be performed on an automotive lathe.
- Always replace the brake pads at the same time as installing new discs or regrinding old discs.