Good brakes are a critical element for ensuring the
safe operation of equipment. The brake system applies
to all vehicles or equipment, such as pickup trucks,
jeeps, tractor-trailers, and construction equipment.
Braking systems must not only stop the unit but also
must stop it in a smooth, uniform motion.
Friction is the resistance in relative motion between
two surfaces in contact with each other. When a
stationary surface is forced into contact with a moving
surface, the rubbing action between the two surfaces
slows down the moving surface. In nearly all brake
systems, the brake drums provide the moving surface,
and the brake shoes provide the stationary surface. The
friction between the brake drum and the brake shoes
slows the drum and wheel; and the friction between the
tire and the road surface slows and stops the vehicle.
Part of your prestart and operator maintenance
responsibilities consist of the following:
Using the proper brake fluid
Checking the brake fluid level
Inflating tires properly
Checking for loose connections or parts
Checking for leaks in the system
Draining air reservoirs daily
Checking the self-contained lubricating oil
system of air compressors daily
Brake troubles in vehicle operations that you may
encounter and must document are as follows:
The brake pedal goes to the floorboard with
One brake drags.
All brakes drag.
The vehicle pulls to one side when braking.
Soft or spongy pedal.
Excessive pedal effort required.
Air in the system.
Loss of brake fluid.
The brakes heat up during driving and fail
Leaky brake cylinders.
Grabbing braking action.
The brake pedal can be depressed without
slowing the vehicle.
On modern equipment, individual service brakes
are provided for each wheel and are operated by a foot
pedal. The equipment also has an emergency or parking
brake. The parking brake is operated by a separate pedal
or a hand lever.
Individual brakes are classified as the external
contracting brake, the internal expanding brake, the disc
brake, and the mechanical parking brake.
External Contracting Brakes
External contracting brakes are sometimes used for
parking brakes on motor vehicles, for cranes, and for
controlling the speed of auxiliary equipment drive
In operation, the brake band (or shoe) of an external
contracting brake is tightened around the rotating drum
by moving the brake lever. The brake band is made of
comparatively thin, flexible steel, shaped to fit the drum,
with a frictional lining riveted to the inner surface (fig.
3-38). his flexible band cannot withstand the high
pressure required to produce the friction needed to stop
a heavily loaded or fast-moving vehicle, but it works
well as a parking brake or hold brake.
Figure 3-38.-External contracting brake.