Chevrolet Light Duty Truck 1973 Service Manual page 307

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
electrical circuit is defective.
4. Turn ignition key off.
5. Replace bulb or repair circuit as 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 master cylinder reservoirs are
full.
NOTE: When bleeding the brakes; the pin in
the 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 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
(fig- 29).
"
See Caution" on Page 1 of t h i s
CAUTIO N:
s e c t i o n .
2. Turn ignition key "ON". Open bleed screw while
helper applies heavy pressure to brake pedal.
Warning lamp should light. Close bleed screw
before helper releases pedal.
NOTE: To "reset" switch, apply heavy pedal
force. This force will apply hydraulic pressure
which re-centers the switch contact.
3. Attach bleeder hose to front brake bleed screw and
repeat Step 2.
4. Turn ignition key off. See Note under Step 2.
5. Lower vehicle to floor.
NOTE: If warning lamp does not light
during Steps 2 and 3 but does light when the
parking brake is set, warning light switch is
defective. Do not attempt to repair switch. A
defective switch must be replaced with a new
combination valve assembly.
Caution should be taken t o prevent
CAUTIO N:
air from entering system during checks on
switch.
The recommended checking interval should be 24
months or 24,000 miles, any time major brake work is
done or any time a customer complains of excessive
pedal travel.
BRAKE TRAVEL WARNING SWITCH (Fig.
74)
Vehicles with frame mounted vacuum over hydraulic
boosters have an electrical switch that senses pedal
travel. This switch will illuminate the lamp on the
instrument panel whenever the brake pedal is in excess
of 5.10 inches.
Removal
1. Loosen the nut (at the switch) on the failure
warning switch push rod and drop the push rod out
of the way.
2. Remove the switch electrical lead.
3. Remove the two switch mounting screws and
remove switch.
Installation
1. Install the switch to the brake pedal bracket with
two screws and install the electrical lead.
2. Check the length of the failed switch push rod to
see that it is as described in Figure 74.
3. Adjust the switch so that the warning light will be
on after 5.10" pedal pad travel in the following
manner.
NOTE: The brake pedal to master cylinder
push rod will have to be removed to make
test to determine if the switch is properly set.
Adjust the brake pedal push rod travel as
described in this section upon completion of
installation.
4. With brake pedal hard against rubber bumper (A),
rotate brake failure warning switch lever (B)
forward and insert the preassembled push rod (C)
in the switch and brake pedal and lock in place.
BRAKES 5-41
LIGHT DUTY TRUCK SERVICE MANUAL