How Do Drum Brakes Work?


Quick Answer

Drum brakes work by pressing brake shoes against the inside of a drum-shaped cylinder attached to the wheel of the vehicle. The friction produced by this contact slows the wheel, slowing down the vehicle. Drum brakes are most common on older vehicles. On newer vehicles, they are often attached to only the rear wheels, and more-efficient disc brakes slow the front wheels.

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Full Answer

A drum brake is essentially an open-ended cylindrical structure attached to each wheel. When the brake is not engaged, a series of springs and actuators hold two semicircular brake shoes away from the walls of the cylinder, allowing the wheel to spin freely. When the brakes are applied, the shoes press outward, contacting the walls of the cylinder and applying friction.

Drum brakes are generally cheaper than disc brakes, but wear out faster due to a larger friction area and more moving parts. As the brake shoes wear out, more force is needed to press them into the walls of the cylinder, which requires more pressure on the car's brake. Commonly, drum brakes have a self-adjusting piston that extends as the shoes wear out in order to balance this wear and ensure the brakes fully engage when applied.

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