The most common cause for a vehicle to shake when the brake is applied is a worn or warped rotor. Other causes include bad shock absorbers, worn bushings or degraded suspension components.
RepairPal experts state that distortions as small as three or four one-thousandths of an inch in size can cause the brake pedal to pulse, and make the whole vehicle shake. The rotor works by clamping down on the wheel and applying friction to slow the vehicle down. A tremendous amount of heat is generated during this process, and temperatures can exceed 500 degrees. Over time, the exposure to heat wears away at the rotor. To determine if a worn rotor is the cause of the vibration, the rotors are measured for uniform thickness and run-out.
A damaged rotor is repaired by machining it on a brake lathe. Resurfacing the rotor eliminates defects causing the vibration, but also thins the surface rendering it more vulnerable to heat exposure. If the rotor is too badly damaged to machine, the mechanic will replace it. While the sensation is unsettling, according to Autohub360, the issue is more of an annoyance than a safety hazard because the brakes themselves are not affected. If the mechanic does not find distortions in the rotors, the problem may be due to worn bushings or wear and tear to the suspension.