Brake pedal vibration

1. When applying the brakes, a pulsating force tries to push the brake pad back. The pulsation is transmitted to the brake pedal.
2. The following are the main possible causes of brake judder:

Due to an excessive runout (side-to-side wobble) of the disc plate, the thickness of the disc plate is uneven. 

1. If the runout is more than 0.04 mm {0.002 in} at the position 10 mm {0.39 in} from the disc plate edge, uneven wear occurs on the disc plate because the pad contacts the plate unevenly.
2. If the runout is less than 0.04 mm {0.002 in}, uneven wear does not occur.

The disc plate is deformed by heat. 

1. Repeated panic braking may raise the temperature in some portions of the disc plate by approx. 1, 000 °C {1, 832 °F}. This results in a deformed disc plate.

Thickness and friction coefficient of the disc plate change due to corrosion. 

1. If the vehicle is parked in damp conditions for a long time, corrosion occurs on the friction surface of the disc plate.
2. The thickness of the corrosion is uneven and it sometimes appears like a wave pattern, which changes the friction coefficient and causes a reaction force.