Chevrolet Light Duty Truck 1973 Service Manual page 274

5 -8 BRAKES
SWITCH TERMINAL
FRONT INLET PORT-^ SWITCH PISTON
FRONT OUTLET
PORT
BOOT
DIAPHRAGM
FRONT OUTLET PORT
Fig. 11 -Brakes Not Applied
the combination valve reduces the rear brake pressure
and delays the rear wheel skid.
Normal Brake Stops (Fig. 15)
The proportioner does not operate during normal brake
stops. Fluid normally flows into the proportioner,
through the space between the piston center hole and
valve stem, through the stop plate and out to the rear
brakes. The spring loads the piston so that it rests
against the stop plate for normal brake pressures.
SWITCH PIN
'METERING VALVE SEAL
METERING VALVE STEM
Fig. 10--Combination Valve
FROM MASTER CYLINDER
,REAR INLET PORT
VALVE STEM
DETENT
PROPORTIONING NUT'
Fig. 1 2 -Shut-Off Point
Proportioning Action (Fig. 16)
Pressure developed within the valve pushes against the
large end of the piston and when sufficient to overcome
the spring load, moves the piston to the left. The piston
"Contacts" the spherical stem seat and starts proportion­
ing by restricting pressure through the valve.
Overhaul and Major Service
The combination valve is not reparable. If a defect is
PROPORTIONER PISTON
STOP PLATE
REAR OUTLET PORT
LIGHT DUTY TRUCK SERVICE MANUAL