CARS.COM — When it comes to brakes, there are no good vibrations. The most likely reason that you feel vibrations through the brake pedal is because a brake rotor — the rotating disc that the brake pads are pressed against by the calipers to slow the wheel — is unevenly worn, or what some call "warped." (It's unlikely that a rotor could truly be warped from normal use as opposed to a manufacturing defect, but thinner and thicker sections — uneven wear — have the same effect as warping and can cause the rotor to vibrate or shake.)
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Brake vibration, or what can also be referred to as a shaking or pulsation, often is the result of parts of the disc brake's rotor being thinner than others instead of uniform all around. As the brakes are applied, the brake pads will be pressed by the calipers against high and low spots that the driver feels through the pedal or steering wheel. Rust and dirt also can build up on a rotor and cause minor vibrations in the vehicle.
A rotor's thickness needs to vary by only a few thousandths of an inch for the driver to feel vibration through the brake pedal or steering wheel. In more serious cases of warped rotors, the whole vehicle can shake or the steering pull when the driver hits the brakes.
One cause of distorted rotors is that the brake pads, the friction material that gets pressed against the rotors, aren't being fully released by the calipers when you remove your foot from the pedal and cause friction as the wheel rotates. If the vehicle's pads "drag" on the rotors too long, the brake rotor and/or the pads can become damaged.
In some cases, warped rotors can be resurfaced (machined) on a brake lathe to create a smooth, even rotor finish, to stop the shaking provided there is enough thickness left in the rotor. Resurfacing rotors to make them smooth requires scraping off the top layer of metal. If too much of the rotor thickness already has been used up, then the rotor should be replaced with a new rotor to cure the brake vibration.
Rather than disc brakes with rotors front and rear, some vehicles' rear wheels still have drum brakes in which brake shoes (essentially curved brake pads) are pressed outward against the walls of the drum to slow the wheel. The drums also can wear unevenly and vibrate. Those vibrations or shaking in the vehicle might be solved by machining the braking surface.
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