Worn rotors are the most common cause of shaking while braking. But there are other potential reasons for the sensation, as well. Here’s a quick review of possible causes:
Warped Brake Rotors
Most modern cars have disc brakes, although some have discs in the front and drums in the rear. Pressing the brake pedal forces the brake pads to squeeze against rotor, creating the friction needed to stop the vehicle.
Over time, the brake rotors can develop a variation in thickness (also known as parallelism). The variation of thickness of the rotor then causes it to wobble side-to-side as it rotates.
If your vehicle has drum brakes am out of round brake drum could be the cause
Some vehicles, like trucks still have drum brakes in the rear. When the brake is pressed a pair of brake shoes are forced outward against a brake drum, creating friction. Brake drums that are worn out of round can cause a shaking or shimmy sensation when the brakes are applied.
Loose (worn) wheel bearings
There is a wheel bearing behind each of your car’s wheels. Because the wheel hub also serves as a mounting spot for the disc brake, a bad wheel bearing can lead to excessive movement that you feel as a shaking sensation while braking.
Worn suspension components
In some cases, worn suspension components can cause a shaking while braking. The sensation may be felt in the steering wheel and/or brake pedal.
For example, problems with the strut assembly can cause a shaking while braking.
Worn brake pads
Pulsation and shaking can occur whenever the pads don’t apply evenly against the brake rotor. That means worn pads also have the potential to cause shaking when the brakes are applied.