Pontiac FIREBIRD 1972 Service Manual page 500

DISC BRAKES 5E-5
WITH BRAKE APPLIED
COOL ROTOR FRICTION ON ROTOR
FIRST CONTACTS CAUSES IT TO HEAT
Fig. 5E-3 Disc Brake Heat Patterns
In actual practice the application and release of the brake
pressure causes a very slight movement of the piston and
claiper. Upon release of the braking effort, the piston and
claiper merely relax into a released positon. The shoes do
not retract any appreciable distance from the rotor sur-
faces.
As the brake lining wears, the piston moves out of the
caliper bore and the caliper repositions itself on the
mounting bolts. In this manner, disc brakes are self-
adjusting.
Some inherent features of disc brakes are:
1. They are self-adjusting.
2. They are less subject to fade than are drum brakes
because heat expansion pushes the rotor into, rather
than away from the linings.
3. The centrifugal force of the spinning rotor allows the
disc to throw off water.
4. Disc brakes are less subject to pull because they do
not have the inherent self-energizing feature of drum
brakes.
Disc-Brake Pad Wear
Disc brake linings normally wear more in the front of the
lining than in the back (tapered wear). This is due to the
presence of greater heat in the front as illustrated in Fig.
5E-3. The rate and the type of wear will vary considerably
with driving conditions.
COMBINATION VALVE
A two function or three function combination valve is
used on all cars equipped with disc brakes. The two func-
tion combination valve, used on station wagon models and
all B Series vehicles, combines the functions of the front
brake metering (hold-off) valve and distributor switch (the
hydraulic differential pressure switch) into a single hous-
ing. In addition to the above two functions, the three
SWITCH TERMINAL
FRONT MASTER CYLINDER
\
REAR MASTER CYLINDER
INLET PORT
OUTLET PORTS TO
OUTLET PORT TO
FRONT BRAKES
REAR BRAKES
SECTION SECTION
--
Fig. 5E-4 Cross Section of Two Function Combination Valve