Bench Bleeding; Metering Valve; Proportioning Valve; Brake C Om Bination V A L V E - Chevrolet CHEVY VAN G10 SERIES Service Manual

C A U T IO N : See "C autio n"
section.
8
. Install the reservoir diaphragm in the reservoir cover and
install the cover on the m aster cylinder. Assemble the
bail wires in to position to retain the reservoir cover. The
m aster cylinder is now ready for " Bench Bleeding" as
outlined below.

Bench Bleeding

1. Install plugs in b o th outlet ports.
N O T E : Plastic plugs th at come with a replacement
cylinder are recommended for this operation.
2. Clam p the m aster cylinder in a bench vise w ith the front
end tilted slightly dow n.
C A U T IO N : Do n o t tighten
damage to the master cylinder could result.
3. Fill b oth reservoirs w ith clean brake fluid.
4. Insert a rod w ith a sm ooth ro u n d end to the prim ary
piston and press in to com press the piston return spring.
5. Release pressure on rod. Watch for air bubbles in the
reservoir fluid.
6
. R epeat step 5 as long as bubbles appear.
7. R eposition m aster cylinder in vise so th a t the fro n t end is
tilted slightly up.
8
. R epeat steps 4-5-6.
9. Install diaphragm and cover on reservoir.
Installation
1. Assemble the push rod through the push rod retain er, if
it has been disassembled.
2. Push the retainer over the end o f the m aster cylinder.
Assemble new b o o t over push rod and press it down over
the push ro d retainer. Slide new m ounting gasket in to
position.
Secure the m aster cylinder to the dash panel w ith
m ounting bolts.
C A U T IO N : See "C a u tio n "
section.
3. C onnect the push rod clevis to th e brake pedal w ith pin
and retainer.
C A U T IO N : See "C a u tio n "
section.
4. Connect the brake lines to the m aster cylinder.
C A U T IO N : See "C a u tio n "
section.
5. Fill the m aster cylinder reservoirs to the levels shown in
8
Figure . Bleed the brake system as outlined in this
section.
6
. If necessary, adjust the brake pedal free play as outlined
in this section.
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vise too tigh tly as
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B R A KE C O M B IN A TIO N V A L V E
N O T E : The brake com bination valve is a non-
adjustable, non-serviceable valve. If defective it must
be replaced.
Functions

Metering Valve

This section o f the valve operates to " h o ld -o ff' hydraulic
flow to the front disc brakes until a predeterm ined pressure is
reached. This " hold-off" action allows the rear drum brakes to
build up sufficient hydraulic pressure to overcome the force of
their retracting springs. This m etering or hold o ff valve then
provides for balanced braking.
N O T E : When bleeding the brakes; the pin in the
end of the metering portion o f the combination
valve must be held in the open position (n o ta llo w e d
to close). This can be accomplished by installing
Tool J-2 37 09 under the mounting bolt and de­
pressing the pin a slight am ount. Be sure to re­
torque the mounting
J-23709 (Fig. 6).
Warning Switch
The w arning sw itch is the pressure differential ty pe. It is
w ired electrically to the warning lamp on the in strum ent panel
to warn the vehicle o perator o f a pressure differential betw een
the fro n t and rear hydraulic systems. Once the sw itch is
activated " o n," it will n o t " reset" until the defect in the
hydraulic system has been repaired. H ydraulic reset to the
" o f f ' position occurs w ith the application o f equal fro n t and
rear pressures.

Proportioning Valve

The function o f this valve is to prevent prem ature rear
wheel slide. Line pressure is allowed to increase norm ally up to
a certain po int (determ ined by vehicle w eight and braking
distribution). When the predeterm ined pressure is reached, the
valve begins to function and lim it the am o unt o f increase in
hydraulic pressure passed to the rear brakes. This prevents the
rear brakes from locking up before the full effective braking
effo rt is produced by the fro n t disc brakes.
N O T E : In the event o f "fro n t hydraulic system
failure" the proportioning valve has a "b y pass"
feature th at assures full system pressure to the rear
brakes.
Removal (Fig. 42)
1. D isconnect electrical lead.
2. Place dry rags below valve to absorb any fluid spillage.
3. Wipe o ff any dirt and disconnect hydraulic lines from
valve — cover open lines to prevent foreign m atter from
entering the system .
4. Remove m ounting screws and remove valve.
BRAKES 5-23
b o lt after removing Tool
C H E V Y V A N SH O P M A N U A L