SEQUENCE OF EVENTS
pressure is applied to the brake pedal and is transmitted from the push rod to the
piston in the main cylinder,
the primary cup closes the compensating port and fluid is forced
through the holes in the valve
cage, around the lip of the rubber valve cup, into the pipe lines and into the
wheel cylinders. This pressure
forces the pistons in the wheel
cylinders outward, expanding the brake shoes against the drums. As the pedal is
farther depressed, higher
pressure is built up within the hydraulic system, causing the brake shoes to
exert greater force against
the brake drums, Fig. 1.
pedal is released, the hydraulic pressure is relieved and the brake shoe
retracting springs draw the shoes
together, pressing the wheel cylinder pistons inward and forcing the fluid
out of the wheel cylinders back
into the lines toward the main
cylinder. The piston return spring in the main cylinder returns the piston to the
pedal stop faster than the
brake fluid is forced back into the lines, creating a partial vacuum in that
part of the cylinder ahead of
the piston. This vacuum causes a small amount of fluid to flow
through the holes in the piston head,
past the lip of the primary cup and into the forward part of the cylinder.
This action keeps the cylinder filled with fluid at all times, ready for the next brake application.
As fluid is drawn from the
space behind the piston head it is replenished from the reservoir through
the inlet or breather port.
When the piston is in a fully
released position, the primary cup clears the compensating port, allowing excess fluid to
flow from the cylinder into the
reservoir as the brake shoe
retracting springs force the fluid out of the wheel cylinders.
The passenger car emergency brake
lever is located under the dash
on the left of the steering column and is connected to the idler lever
with rod-type linkage. The
idler lever is mounted in two
brackets riveted to the center of the second frame cross member. Two one-piece cables are
pivoted at the center of the
idler lever and are attached
to the rear brakes.
rod from the control lever is yoked at one end of the idler lever and provides
proper torque for emergency brake application, Fig.
properly maintain the braking system, servicemen must appreciate that a thorough