Chevrolet Light Duty Truck 1973, Service Manual

Page: 332 / 979

5 6 6 BRAKES
Fig. 91--Typical Circuit • Holding
VACUUM FAILURE
In case of vacuum source interruption, the brake unit
operates in the following manner:
As the pedal is pushed down, the end of the air valve
contacts the reaction levers and pushes, in turn, against
the hydraulic reaction plate. Since the hydraulic reaction
plate is fastened to the master cylinder piston rod, it
forces the piston rod against the master cylinder primary
piston, which builds up the hydraulic line pressure. With
this condition you have, in effect, a standard brake unit.
M A IN TE N A N C E A N D ADJUSTMENTS
INSPECTIONS
1. Check vacuum line and vacuum line connections as
well as vacuum check valve in front housing of
power unit for possible vacuum loss.
2. Inspect all hydraulic lines and connections at the
wheel cylinders and master cylinder for possible
hydraulic leaks.
3. Check brake assemblies for scored drums, grease or
brake fluid on linings, worn or glazed linings, and
make necessary adjustments.
4. Check brake fluid level in the hydraulic reservoirs.
The reservoirs should be filled to the levels shown
in Figure 31.
5. Check for loose mounting bolts at master cylinder
and at power section.
6
. Check air cleaner filter in power piston extension
and replace filter if necessary.
7. Check brake pedal for binding and misalignment
between pedal and push rod.
LIGHT DUTY TRUCK SERVICE MANUAL