A drum brake is a brake in which the friction is caused by a set of shoes or pads that press against the inner surface of a rotating drum. The drum is connected to a rotating wheel. Some designs have two wheel cylinders.
The modern automobile drum brake was invented in 1902 by Louis Renault, though a less-sophisticated drum brake had been used by Maybach a year earlier. In the first drum brakes, the shoes were mechanically operated with levers and rods or cables. From the mid-1930s the shoes were operated with oil pressure in a small wheel cylinder and pistons (as in the picture), though some vehicles continued with purely-mechanical systems for decades.
The shoes in drum brakes are subject to wear and the brakes needed to be adjusted regularly. In the 1960s and 1970s brake drums on the front wheels of cars were gradually replaced with disc brakes.
Another type of drum brake is where a friction belt is wrapped around the outside of the drum and tightened. This type predated the modern drum brake, and was later often used for the parking brake on the central drive shaft. This type of band brake is also used in automatic transmissions and aerobic exercise cycling equipment.
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