Understanding & preventing brake judder

What is brake judder?

A major cause of brake judder is disc thickness variation (DTV). This is often misinterpreted as ‘warped discs’. Disc thickness variation (DTV) is the term used for the variation in thickness on the friction faces of the brake disc. DTV occurs when the Brake Disc becomes worn in a single area of the disc surface.

This wear is caused by excessive run-out during installation of the disc due to corrosion of the hub face and /or wheel studs, elongated bolt holes or the presence of foreign matter or debris, for example those found in copper based grease products.

What are the symptoms of brake judder?

Initially none, but ‘run-out’ will cause DTV and then judder and vibration during braking, typically after approx. 2000-4000 miles.

Although excessive run-out is a major factor in the generation of DTV It is equally important to check the following:

  1. Check the brake caliper pistons for any signs of sticking or seizure.
  2. Check the brake caliper slide pins and bushes, where fitted, for excessive wear or stiction.
  3. Where pad guided calipers are fitted, check the caliper mounting bracket pad abutment faces for wear.
  4. Check all steering and suspension joints / bushes for excessive play.
  5. Check the front wheel bearings for correct adjustment and excessive play, ( Refer to manufactures’ workshop manual for adjustment procedure).
  6. Check for damaged wheels / tyres, incorrect wheel nut / stud torque and wheel imbalance.

Installation tips to avoid brake judder

  • Always replace discs in axle sets to ensure even braking.
  • Clean away debris trapped between hub and disc mounting faces which will cause run-out, leading to DTV (thick/thin) and Judder.
  • Check that the disc thickness is not less than that indicated on the edge-marking of the disc.
  • Check the braking surface of the disc for damage or scoring – replace as necessary.
  • Thoroughly clean the faces of the new discs to remove the protective coating (not painted discs).
  • Ensure that the caliper carrier is clean, and that the pads are able to move freely in the caliper.
  • Check discs for run-out with a DTI.
  • Avoid heavy braking for the first 200 miles to allow your new pads to bed in and maximise their performance.