Lesson 1/Learning Event 1
When a brake shoe or a brake band is applied against the outside of a
rotating brake drum, the brake is known as an externalcontracting
brake. On this type of brake, the nonrotating braking surface must
be forced inward against the drum to produce the friction necessary
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.