Warning Switch; Proportioning Valve; Brake Warning Light Checking; Testing Warning Switch - Chevrolet 10 1971 Series Chassis Service Manual

HOLD D O W N
PIN
Fig. 51— Rear Brake - Used with R.P.O. H-22
parts together by installing the clip in groove of pin.
7. Fasten two brake shoes and linings together by in­
stalling connecting spring. Move the shoes toward
each other and install adjusting screw.
8. Lubricate the backing plate contact surfaces. (Very
light coat of lube).
9. Place shoe and linings in position on backing plate.
When facing the brake assembly, the
NOTE:
shoe with the short lining should be to the left
with the lever assembled to it.
10. Pull brake shoes apart and install strut lever and
spring between them. The loop on the strut spring
should be in the "up" position.
11. Install hold down pins, washers, springs and cups
from backing plate to shoes.
12. Place guide plate on anchor pin.
13. Install pull back springs.
14. Remove the "knock out" plug (if necessary) and
install a rubber plug in the brake drum adjusting
hole.
15. Install the brake drum.
16. Install the propeller shaft.
BRAKE CO M BINATIO N VALVE
Metering, Warning and Proportioning (Fig. 50)
The brake combination valve is a non-
NOTE:
adjustable, non-serviceable valve.
it must be replaced.
Function
Metering Valve
This section of the valve operates to "hold-off" hy­
draulic flow to the front disc brakes until a predeter-
minded pressure is reached.
allows the rear drum brakes to build up sufficient
hydraulic pressure to overcome the force of their re­
tracting springs. This metering or hold off valve then
provides for balanced braking.
When bleeding the brakes; the pin in the
NOTE:
end of the metering portion of the combination
valve must be held in the open position (not
ACTUATING LEVER
ADJUSTING C A M
ACTUATING
LEVER LINK
OVER RIDE
LEVER
RETURN
\ SPRING
ACTUATING
LEVER
If defective
This " hold-off" action
allowed to close). This can be accomplished by
installing tool J-23709 under the mounting bolt
and depressing the pin a slight amount. Be sure
to re-torque the mounting bolt after removing
tool J -23709.

Warning Switch

The warning switch is the pressure differential type.
It is wired electrically to the warning lamp on the
instrument panel to warn the vehicle operator of a pres­
sure differential between the front or rear hydraulic sys­
tem. Once the switch is activated "on",
"reset" until the defect in the hydraulic system has
been repaired. Hydraulic reset to the "off" position
occurs with the application of equal front and rear
pressures.

Proportioning Valve

The function of this valve is to prevent premature rear
wheel slide. Line pressure is allowed to increase nor­
mally up to a certain point (determined by vehicle weight
and braking distribution). When the predetermined pres­
sure is reached, the valve begins to function and limit
the amount of increase in hydraulic pressure passed to
the rear brakes. This prevents the rear brakes from
locking up before the full effective braking effort is
produced by the front disc brakes.
In the event of "front hydraulic system
NOTE:
failure" the proportioning valve has a "by pass"
feature that assures full system pressure to the
rear brakes.
Removal
1. Disconnect electrical lead.
2. Place dry rags below valve to absorb any fluid
spillage.
3. Wipe off any dirt and disconnect hydraulic lines from
valve - cover open lines to prevent foreign matter
from entering the system.
4. Remove mounting screws and remove valve.
Installation
1. Make sure new switch is clean and free of lint. If any
doubt exists, wash the switch in denatured alcohol
or brake fluid and allow to dry.
2. Place new switch in position and secure with screws.
3. Connect hydraulic lines to valve.
4. Connect switch electrical lead.
5. Bleed the brake system.

Brake Warning Light Checking

1. Set parking brake and turn the ignition key to "ON" .
2. Warning lamp should light.
3. If lamp does not light: bulb is burned out or elec­
trical circuit is defective.
4. Turn ignition key off.
5. Replace bulb or repair circuit if necessary.

Testing Warning Switch

1. Raise vehicle on a hoist and attach a bleeder hose to
a rear brake bleed screw and immerse the other end
of hose in a container partially filled with clean
brake fluid. Be sure main cylinder reservoirs are
full.
When bleeding the brakes; the pin in the
NOTE:
end of the metering portion of the combination
valve must be held in the open position (not
allowed to close). This can be accomplished by
BRAKES 5-25
it will not
10-30 CHEVROLET TRUCK SERVICE MANUAL