Brake disc run out is the measurement of how much the brake disc is warped or bent. It is important to check brake disc run out because it can affect the braking performance of the vehicle. If the brake disc is warped or bent, it can cause the brake pads to make uneven contact with the disc, which can lead to reduced braking power and increased brake wear.
There are a few different ways to check brake disc run out. One way is to use a dial indicator. A dial indicator is a precision measuring tool that can be used to measure the distance between two surfaces. To use a dial indicator to check brake disc run out, the dial indicator is mounted on the brake caliper and the tip of the dial indicator is placed on the brake disc. The dial indicator is then rotated around the brake disc and the run out is measured.