How Your Brakes Work

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Unlocking the Secrets of the Braking System
An anti-lock brake system has sensors on the wheels that report to a computer when a particular brake locks up or begins to skid on the pavement. If a lockup occurs, a computer takes over and orders the system to begin pulsing the brake, in a somewhat similar fashion to a manual pumping of the brake to prevent a loss of control.

But in an anti-lock system, the pulsing is very quick-roughly 12 times per second. Every system works differently, but generally the pulsing occurs so quickly that you could not really detect it from the feel of the brake pedal.

If you experience a pulsing or jerking from the brake, it is far more likely that it was caused by a defect in the brake rotor or drum than it was from the anti-lock system. A warped rotor or out-of-round drum can cause pronounced pulsating in the brake pedal.

The failure of the pad to retract is not uncommon. In older drum systems, the brake shoes are pulled back from the drum by strong springs. But in a disk brake system, the pads are pulled back from the rotor (or disk) by the resiliency of rubber seals. As these seals age or are damaged by contaminated brake fluid, they can fail to do their job. The result is that the pad will ride against the rotor and wear out prematurely.

If your rotor is warped, it can cause the pad to wear out even without a failure of the rubber seal. A warped rotor will wobble as it rotates, thereby scraping the pad as it turns. Eventually the pad wears out and the metal backing plate will damage the metal rotor.

Pads no longer contain asbestos, but that does not mean they wear out faster. The new semi-metallic pads are quite hard and actually outlast the older asbestos pads. In addition, they don't cause lung cancer.

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