GMC 4000 Series Service Manual page 219

Sec. 5B
Page 212
AIR BRAKES
4. Depress and hold brake pedal in full-down
position.
5. Turn adjusting bolt and stop plate assembly
up until plate contacts brake pedal, with pedal in
full-down position.
6. Release brake pedal and turn adjusting bolt
and stop plate assembly up (toward brake pedal)
three full turns.
7. Hold adjusting bolt and stop plate assembly
and tighten lock nut.
8. Start engine and build up air pressure in
system .
9. Check operation of brake pedal. Make sure
pedal contacts stop plate before piston bottoms in
application valve.
BRAKE LINING WEAR ADJUSTMENT
(Refer to Fig. 6)
NOTE: On vehicles equipped with "Stopmaster"
brakes, brake shoe adjustment is covered under
"Stopmaster Brakes" near end of this section.
Slack adjusters functioii as adjustable levers
and provide a quick and easy method of adjusting
the brakes to compensate for normal lining wear.
Positive-locking type slack adjusters are used on
all vehicles. Internal construction of all slack ad­
justers is as shown in figure 7; however, lever
arm (body) may be offset to suit installation re­
quirements. Refer to "Air Brake Specifications"
at end of this section to determine slack adjuster
type used.
The most efficient brake action with "S" cam
brakes, will be obtained when the arm travel of the
slack adjuster is held to a minimum so that the
full length of the lever is utilized during brake ap­
plication. Minor adjustment to compensate for
normal lining wear should be confined to the slack
adjusters.
G M C S E R V I C E M A N U A L
as possible without brakes dragging (refer to fig.
6). Push rod travel should be checked after every
2,000 miles of operation to determine whether ad­
justment is necessary. Brake linings should be re­
placed before wear exposes rivet heads and causes
drum damage.
worm shaft until brake drags, then back off until
wheel turns freely.
jvorm shaft can be turned (fig. 7). Make sure sleeve
is pushed in far enough to clear hex end of worm
shaft before turning shaft.
fully released. After completing adjustment, make
sure lock sleeve comes out and engages hex end
of worm shaft (fig. 7). Pry sleeve out with screw ­
driver if necessary. Coat lock sleeve and end of
worm shaft with wheel bearing grease to keep out
dirt and moisture to assure free movement of
sleeve at next adjustment.
SLACK ADJUSTER OPERATING TEST
ers rotate freely and without binding. Release
Figure 7—Slack Adjuster
Push rod travel should be maintained as short
1. With wheel jacked up, turn slack adjuster
NOTE: Lock sleeve must be pushed in before
2. Be sure wheel turns freely with brakes
SLACK ADJUSTERS
Apply brakes and make sure all slack adjust­