Chevrolet 1977 light duty truck Service Manual page 394

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 m ade with the brake pedal
firmly depressed (approxim ately 90 lbs.) while the brakes
are cold.
C-K-G M a n u a l .........4.5"
C-K-G P o w e r.........3.5"
P (Except J F 9 ) ...... 3.5"
P ( J F 9 ) .............. 6.0"
O n power brake-equipped vehicles, p u m p the pedal
a m inim um o f 3 times with the engine off before making
pedal travel checks. This exhausts all vacuum from the
power booster.
STOP LIGHT SWITCH
Adjustm ent
The stop light switch is mounted on a flange
pro truding from the brake pedal support.
1. Release the brake pedal to its normal position.
2. Adjust switch by turning in or out as necessary.
Electrical contact should be made when the brake
pedal is depressed 1.0-1.24" (C-K models), .70" (G-P
models) from its fully released position.
3. Tighten switch locknut, if so equipped, and
connect electrical harness.
BLEEDING AND FLUSHING BRAKE SYSTEM
Bleeding Brake Hydraulic System
A bleeding operation is necessary to remove air
w henever it is introduced into the hydraulic brake
system.
It m ay 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 m aster cylinder and wheel cylinders, then all
wheel cylinders served by the disconnected pipe must be
bled.
M anual Bleed
If the vehicle is equipped with power brakes, deplete
the vacuum reserve by applying the brakes several times.
1. Fill m aster cylinder with brake fluid and keep at
least on e-half full o f fluid du rin g bleeding operation.
Bleed right rear brake, left rear brake, right front
brake and left front brake.
2. W ith the proper size box end wrench or Tool
J-21472 over bleeder valve, attach bleeder tube to valve
and allow tube to hang subm erged in brake fluid in a
clean glass j a r (fig. 5-1).
ON-VEHICLE SERVICE
3.
brake pedal.
4.
5.
Check
required to prevent air from being drawn through
master cylinder.
6.
the entire system is to be bled.
7.
and repeat entire bleeding procedure if necessary.
Flushing Brake Hydraulic System
It is recom m ended that the entire hydraulic system
be thoroughly flushed with clean brake fluid whenever
new parts are installed in the hydraulic system.
Flushing is also recom m ended if there is any doubt
as to the grade of fluid in the system. If fluid has been
used which contains the slightest trace of mineral oil, all
ru bber parts that have been subjected to the contam i­
nated fluid should be replaced.
BRAKE PIPES
Replacement (Figs. 5-2 thru 5-4)
Open the bleeder valve and fully depress the
Close bleeder valve and release brake pedal.
Repeat steps 3 and 4 until all air is evacuated.
and refill master
Repeat the bleeding procedure at all wheels if
Check the brake pedal, feel for "sponginess"
W A R N IN G : NEVER USE COPPER T U B IN G
BECAUSE COPPER IS SUBJECT TO
FATIGUE
CRACKING A N D C O RRO SION W H IC H
COULD RESULT IN BRAKE FAILURE.
cylinder reservoir as