Many of today’s vehicles have brake systems where the disc rotors are of a ‘hat’ design. While these designs are generally easier to service they can, at times, create some customer dissatisfaction due to brake pedal pulsation during the brake application.
If the vehicle is equipped with ABS, some pedal feedback and noise is normal during panic stops or when braking on wet or slick surfaces. But you should not experience any ABS pedal feedback when braking normally on dry pavement.

Brake pedal pulsation is most often the result of disc thickness variation worn into the rotor. Disc thickness variation (DTV) is the technical term for a rotor that is not uniformly thick.
Quality rotors are uniformly thick when new, and will stop the vehicle smoothly. However, due to other potential irregularities in the braking system, DTV can develop over time and eventually lead to brake pedal pulsation.
The most common cause of DTV is rust scale or debris between the hub and rotor mounting surfaces. This can cause the rotor not to sit flat resulting in excessive lateral runout greater than 0.08mm.
Measuring with a dial indicator will confirm the diagnosis.



There is however, the rare occasion where the issue may not lie within the brake rotor at all.
An error as seemingly harmless as over-torqueing or unevenly torqueing the wheel nuts – especially with an impact wrench – can cause a rotor to wear unevenly, resulting in DTV.
In the same vain as a dirty hub face, the mounting face of the wheel could be corroded or dishevelled preventing a uniform fit. A bad wheel bearing or bent axle shaft, as well as twisted brake lines can be of root cause to DTV.
Do be mindful that when it comes to your car’s braking system, the most important thing to remember is that safety comes first.

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