Pontiac FIREBIRD 1972 Service Manual page 413

5-10 1972 PONTIAC SERVICE MANUAL
GUIDE STRUT RETURN
ACTUATING
A
LINK.
A
ACTUATING
A D J ~ S T E R
CONGCTING
SPRING AND
LEVER SPRING WASHER
REAR
RETURN WHEEL CYLINDER
WHEEI
I
SOCKET
STAR
AJUSTING
WHEEL SCREW NUT
FRONT
Fig.
5-3
Typical Right Hand Self-Adjusting Brake Assemblies
If the brake linings are worn enough to allow the second-
ary shoe to move, the adjuster lever will turn the adjusting
screw star wheel one or two teeth, depending on amount
of lining wear. If the secondary shoe does not move, ad-
juster lever movement will not be enough to rotate the
adjusting screw star wheel.
When brakes are released, the actuating lever return
spring will reposition the actuating lever into adjusting
position on the adjusting screw star wheel.
An override feature is incorporated into the self-adjusting
brake which allows the secondary shoe to be applied in
reverse in event the adjusting screw is frozen.
When the car is moving forward and brakes are applied,
the upper end of the secondary shoe is forced against the
anchor pin, and the self-adjuster does not operate.
HYDRAULIC SYSTEM
Depressing the brake pedal moves the master cylinder
push rod and pistons, forcing hydraulic fluid out through
the hydraulic lines into the wheel cylinders, (Fig. 5-18)
forcing the wheel cylinder pistons outward and expanding
the brake shoes against the drums.
When the brake pedal is released quickly, the master cyl-
inder pistons return to the released position faster than
fluid returns from the lines. Holes in the piston heads
allow fluid to pass from the rear to the front of the piston
heads, past the primary cups to fill in this space. At the
same time the brake shoe return springs force the wheel
cylinder pistons to return. Fluid forced out of the wheel
cylinders by this action returns to the master cylinder. As
this fluid returns, the excess portion will return to the
reservoir through the compensating ports which are un-
covered when the master cylinder pistons are in the
released position.
PARKING BRAKE
When the parking brake lever is depressed the cables con-
nected to the rear brakes are pulled taut. Each rear brake
cable attaches to an actuating lever which pivots at a hole
in the secondary shoe web. When the lever is moved for-
ward by the brake cable, it engages a strut which forces
the primary shoe against the brake drum. After the pri-
mary shoe is applied, the secondary shoe is then forced
against the drum.
The rear brake assemblies serve a dual purpose in that
they are utilized both as a hydraulically operated brake
and a mechanically operated parking brake. Adjustment
of the hydraulic brake, also adjusts the parking brake.
NOTE:. Automatic brake adjusters nonnally
keep the parking brake adjusted correctly.
No wever, there may be a condition where the
parking brake system will require additional
adjustment even though the service brakes are
perfectly satisfictory.