What is the Brake Judder?
While the car is traveling at middle speed or high speed there is a frequent vibration on the car body, the steering wheel and the brake pedal when the brake pedal is depressed lightly. The vibration will disappear when the brake pedal is released, it means the brake judder, also called as brake shimmy by some. This is cause by a certain speed regardless where the gear is positioned and the speed of the engine.
The steering wheel vibration can either be rotation which means towards the turning of the steering wheel or in random direction. The main factors that causing the vibration is either the change of thickness on or run-out of brake rotor this will result to brake pad vibration that will also causes a change in pressure of the brake fluid. When the brake pedal or the steering system vibrates, the steering wheel or the vehicle will also vibrate in an up and down rotational direction.
Even when the brake pedal is depressed with fix strength, the area of the brake pedal where the thickness is larger than other portion will moves in the outward direction every time there is a big change in thickness of the rotor, the brake pad on the portion where the thickness is lesser will move in the inward direction.
At the same time the inside pressure will then cause the change in brake fluid pressure. If the run-out is too big and the brake pad is slanted towards the center of the rotational direction the brake pads will moves in the right direction. With the case of the brake pad slanted to the left the brake pad will move in the left direction that will result on the change in the inside pressure of the brake fluid.