Drum Brakes

The humble drum brake ruled the brake world in the 1950s till the 1980s and was eventually superceeded by the disc brake system. Although more complicated in construction, its concept is simpler. Two semicircular brake shoes sit inside a spinning drum which is attached to the wheel. When you apply the brakes, hydraulic fluid is pumped into a pistion between the pair of semi-circular brake shoes. These shoes are expanded outwards to press against the inside of the drum. This creates friction, which creates heat, which transfers kinetic energy, which slows down the car. After taking one's foot off the brake pedal there is a return spring that pulls the shoes back away from the surface of the brake drum.
The drum brake is actually highly efficientin its operation, generating lots of retardation with little pedal effort especially for its size. However its non linear retardation and its inability to handle a lot of heat allowed the disc brake to rise to popularity.

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