GMC 1982 Light Duty Truck, Service Manual

Page: 530 / 1435

5-10 BRAKES
ON-VEHICLE SERVICE
PEDAL TRAVEL
At reasonably frequent intervals, the brakes should be
inspected for pedal travel, which is the distance the pedal
moves toward the floor from a fully-released position.
Inspection should be made with the brake pedal firmly
depressed (approximately 90 lbs.) while the brakes are cold.
• C-K-G M a n u a l......... 4.5 " (1 1 5 mm)
• C-K-G P ow er.......... 3.5" (90 mm)
• P (Except J F 9 ) ....... 3.5" (90 mm)
• P (J F 9 )............... 6.0" (150 mm)
On power brake-equipped vehicles, pump the pedal a
minimum of 3 times with the engine off before making pedal
travel checks. This exhausts all vacuum from the power
booster.
STOP LIGHT SWITCH
A d ju stm e n t (Fig. 5-3)
The design of the switch and valve mounting provides
for automatic adjustment when the brake pedal is manually
returned to its mechanical stop as follows:
1. With brake pedal depressed, insert switch and/or valve
assembly into tubular clip until switch body and/or
valve assembly seats on tube clip. N ote that audible
"clicks" can be heard as threaded portion of switch
and valve are pushed through the clip toward the brake
pedal.
2. Pull brake pedal fully rearward against pedal stop,
until audible "click" sounds can no longer be heard.
Switch and/or valve assembly will be moved in tubular
clip providing proper adjustment.
3. Release brake pedal, and then repeat Step 2 to assure
that no audible "click" sounds remain.
Electrical contact should be made when the brake
pedal is depressed 1.0-1.24" (25-31 mm) (C-K
models), .45-.95" (11-24 mm) (G-P models) from its
fully released position.
BLEEDING AND FLUSHING BRAKE SYSTEM
Bleeding Brake Hydraulic System
A bleeding operation is necessary to remove air
whenever it is introduced into the hydraulic brake system.
It may be necessary to bleed the hydraulic system at all
four wheel cylinders if air has been introduced through low
fluid level or by disconnecting brake pipes at master
cylinder. If brake pipe is disconnected at any wheel cylinder,
then that wheel cylinder only need be bled. If pipes are
disconnected at any fitting located between master cylinder
and wheel cylinders, then all wheel cylinders served by the
disconnected pipe must be bled.
Time required to bleed the hydraulic system when the
master cylinder is removed can be reduced if the master
cylinder is filled with fluid and as much as as possible is
expelled before the cylinder is installed on the vehicle.
M a n u a l B le e d in g
With power brakes, remove the vacuum reserve by
applying the brakes several times with the engine off.
1. Fill the master cylinder reservoirs with brake fluid and
keep at least one-half full of fluid during the bleeding
operation.
2. If the master cylinder is known or suspected to have air
in the bore, then it must be bled before any wheel
cylinder or caliper in the following manner:
a. Disconnect the forward (blind end) brake pipe