External- Contracting And Internal - Expanding Brakes

Wheeled Vehicle Braking Systems
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for braking. The brake band is tightened around the drum by moving

the brake lever. Unless an elaborate cover is provided, the

externalcontracting brake is exposed to dirt, water, and other

foreign matter which rapidly wears the lining and drum. This is

particularly true with wheel brakes.

The nonrotating unit may be placed inside the rotating drum with the

drum acting as a cover for the braking surfaces. This type of brake

is known as an internalexpanding brake because the nonrotating

braking surface is forced outward against the drum to produce braking

action. This type of brake is used on the wheel brakes of cars and

trucks because it permits a more compact and economical construction.

The brake shoes and brakeoperating mechanism may be mounted on a

backing plate or brake shield made to fit against and close the open

end of the brake drum. This protects the braking surfaces from dust

and other foreign matter.

Some vehicles are fitted with a third type of brake system known as

disk brakes. The rotating member is known as the rotor. A brake pad

is positioned on each side of the rotor. The brakes operate by

squeezing together and grasping the rotor to slow or stop the disk.