A shaking or pulsating when applying the brake pedal almost always indicates excessive rotor runout or a variation in rotor thickness. Although not quite accurate, many professionals refer to these irregularities as “warped brake rotors.”
Of course, there are also some other, less common reasons why your car might be shaking when braking.
Why Does My Car Shake When I Brake?
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 rundown on five possible causes:
Excessive lateral rotor runout or a variation in rotor thickness (warped brake rotors)
Many modern cars have disc brakes at all four corners, though some have discs in the front and drums in the rear. Pressing the brake pedal forces a pair of brake pads to squeeze against the disc-shaped rotor, creating the friction needed to stop the vehicle.
Over time, the brake rotors can develop irregularities, such as excessive runout or a variation in thickness (also known as parallelism). Runout refers to a distortion of the rotor that causes it to wobble side-to-side as it rotates. Thickness variation, on the other hand, indicates the rotor is thicker in some spots than others.
Both concerns can prevent the pads from pressing squarely against the rotor during brake application. The result is often a shaking/pulsation sensation felt in the brake pedal. Because the brakes mount to the wheel hub, which mounts to the steering knuckle, you may also feel shaking in the steering wheel.
Out of round brake drums (if your vehicle has drum brakes)
Some vehicles still have drum brakes in the rear. With this design, when the driver presses the brake padel, 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/pulsation sensation when the brakes are applied.
Loose wheel bearings
There is a wheel bearing behind each of your car’s wheels. Each wheel bearing allows a wheel hub, which acts as a mounting point for the wheel and tire, to turn as the vehicle is traveling down the road.
Because the wheel hub also serves as a mounting spot for the disc brake, a loose wheel bearing can lead to excessive lateral runout. As a result, you may experience 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, in a strut-style suspension, the brake rotor mounts to the steering knuckle, which, in turn, mounts to the strut. As such, 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 squarely against the brake rotor. That means worn pads also have the potential to cause shaking when the driver applies the brakes.
What to Do About Brake Pedal Pulsation or Shaking
A pulsating or shaking brake pedal can affect braking performance, thereby compromising vehicle safety. You should address the issue as soon as possible.
If you have the know-how, fixing the problem yourself is usually fairly straightforward. But if you have any doubts about your abilities, it’s best to let a professional repair the issue. After all, we’re talking about your brakes here.
And your car’s brakes aren’t something you want to gamble with.