How to

How to check brake disc runout and thickness

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Noise and vibration complaints are often linked to brake disc condition. To diagnose these issues accurately it’s essential to measure both disc runout and disc thickness variation using the correct process and tooling.

In this video, Phil demonstrates how to carry out these checks on an MG ZS. You’ll learn how to:

Check the diagnostic tool for any brake-related service or pressure release routines
Correctly clamp the brake disc to replicate wheel fitment
Use a dial test indicator (DTI) to measure disc runout
Measure disc thickness variation at multiple points using a micrometre
Compare measurements against manufacturer specifications

Braking Diagnostics & Test Equipment Maintenance Solutions How to 1 min read

Why do I need to check the diagnostic tool before working on the brakes?

Some vehicles require specific brake-related routines, such as service modes or pressure release procedures, before components are removed or adjusted. Checking the diagnostic tool first helps ensure the braking system is safe to work on and prevents damage to components.

What is the difference between disc runout and thickness variation?

Disc runout measures how much the brake disc deviates from true rotation as it spins, while thickness variation measures differences in disc thickness around its circumference. Both can contribute to brake vibration, but thickness variation is often a more direct cause of noise and judder.

What tools are needed to check brake disc condition accurately?

A dial test indicator (DTI) is used to measure disc runout, and a micrometre is used to measure disc thickness variation. Correct setup, secure disc clamping and consistent measuring technique are essential for reliable results.