automobiles operates in a way similar to the
system illustrated in figure 2-22.
When the brake pedal is depressed, the
pressure on the brake pedal moves the piston
within the master cylinder, forcing the brake fluid
from the master cylinder through the tubing and
flexible hose to the wheel cylinders. The wheel
cylinders contain two opposed output pistons,
each of which is attached to a brake shoe fitted
inside the brake drum. Each output piston pushes
the attached brake shoe against the wall of the
brake drum, thus retarding the rotation of the
wheel. When pressure on the pedal is released, the
springs on the brake shoes return the wheel
cylinder pistons to their released positions. This
action forces the displaced brake fluid back
through the flexible hose and tubing to the master
cylinder.
The force applied to the brake pedal produces
a proportional force on each of the output
pistons, which in turn apply the brake shoes
frictionally to the turning wheels to retard
rotation.
As previously mentioned, the hydraulic brake
system on most automobiles operates in a similar
way, as shown in figure 2-22. It is beyond the
scope of this manual to discuss the various brake
systems.
Figure 2-22.—An automobile brake system.
2-17
