Chevrolet Light Duty Truck 1973 Service Manual page 328

5 -6 2 BRAKES
In this position there is vacuum on both sides of the
power piston, and the power piston is held against the
rear of the housing by the power piston return spring. At
rest, the hydraulic reaction plate is held against the
reaction retainer. The air valve spring holds the reaction
levers against the hydraulic reaction plate and also holds
the air valve against its stop in the tube of the power
Fig. 8 7 -Typical Circuit - Released
piston. The floating control valve assembly is held
against the air valve seat by the floating control valve
spring.
With the power brake at released position, the master
cylinder primary seals on both the rear (primary) piston
and the floating (secondary) piston are back past the two
compensating ports in the bore.
LIGHT DUTY TRUCK SERVICE MANUAL