What would you use to check the brake disc run out?

To check the brake disc run out, you would use a dial indicator. A dial indicator is a precision measuring instrument that can be used to measure the amount of movement or deflection of an object. It consists of a dial with a graduated scale and a pointer that is attached to a plunger. The plunger is placed against the object being measured, and the dial will indicate the amount of movement or deflection in thousandths of an inch.

To check the brake disc run out, you would mount the brake disc on a mandrel and then use the dial indicator to measure the amount of run out at various points on the disc. The dial indicator should be placed against the edge of the disc and then moved around the circumference of the disc to check for any variations in thickness. The maximum run out should be specified in the vehicle manufacturer's service manual.

If the brake disc run out is excessive, it can cause the brakes to pulsate or grab when applied. This can lead to premature brake wear and reduced braking performance. Checking the brake disc run out is a simple and effective way to ensure that the brakes are functioning properly.