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Sec. 4
Page 56
GM COACH MAINTENANCE MANUAL
AIR BRAKES
to prevent leakage, otherwise the diaphragm will
become distorted and premature failure will re-
sult.
b. With brakes fully applied, check for leak-
age through the diaphragm by coating the push
rod boot and the drain holes in the non-pressure
plate with soap suds. No leakage is permissible.
If
leakage is evident, replace diaphragm.
3. Check Push Rod Travel
Check push rod travel by holding a rule along-
side the push rod while brakes are applied and
released.
If
travel is approaching maximum dimen-
sion given in figure 1, adjust as previously des-
cribed under "Brake Adjustments" in this section.
BRAKE CHAMBER REPLACEMENT
1. Removal
Disconnect air line. Disconnect push rod yoke
from slack adjuster.
Remove mounting nuts and
remove brake chamber.
2. Installation
Mount brake chamber in position and connect
air line. Connect push rod yoke to slack adjuster.
Adjust brakes as previously directed under "Brake
Adjustment."
Apply brakes and made sure push
rods at front brakes are correct length. Angle
formed by push rod and slack adjuster should be
slightly greater than 90 degrees with brakes re-
leased.
If
necessary, adjust push rod length by
screwing yoke onto or off of push rod.
Push rod
must not extend through yoke far enough to inter-
fere with slack adjuster. Test brake chamber as
previously directed under "Serviceability Tests."
BRAKE CHAMBER DISASSEMBLY
Before disassembling brake chamber, mark
the pressure plate and the non-pressure plate so
they may be reassembled with the air inlet open-
ing in correct position. Disassemble brake cham-
bers as follows:
Front (Fig. 10)
1. Remove nuts
edge of diaphragm
non-pressure plate.
diaphragm.
and bolts clamping the outer
between pressure plate and
Remove pressure plate and
2. Remove yoke, lock nut, and boot from
rod, then remove push rod and spring from
pressure plate.
push
non-
Rear
1. Remove nuts
edge of diaphragm
non-pressure plate.
diaphragm.
and bolts clamping the outer
between pressure plate and
Remove pressure plate and
2.
Unscrew push plate from push rod
move push rod, diaphragm spring, seal
spring, and seal washer.
and re-
washer
BRAKE CHAMBER INSPECTION
1.
Clean all metal parts thoroughly, using a
suitable cleaning fluid.
2. Examine diaphragm and replace with new
part
if
any signs of wear or deterioration are
evident.
Diaphragms should be replaced every
50,000 miles, or at least every year.
3. Replace push rod if bent or distorted.
4.
Examine push rod spring and replace if
weak or broken.
When replacing spring, make
sure new spring has the same tension as the
spring in the brake chamber on the opposite wheel,
otherwise, unbalanced braking may result.
5. Replace push rod boot (front only) if de-
teriorated.
BRAKE CHAMBER ASSEMBLY
Front (Fig. 10)
1. Place push rod and spring in non-pressure
plate, install boot on push rod and non-pressure
plate, and install lock nut and yoke on push rod.
2. Place diaphragm on pressure plate. Posi-
tion pressure plate and diaphragm on non-pressure
plate, being sure the air inlet opening in the pres-
sure plate is in proper relation to the mounting
studs as marked before disassembly.
3. Install bolts and nuts holding diaphragm
between plates.
It is important that all bolts be
tightened evenly and not excessively. Tighten bolts
only sufficiently to insure an airtight seal, but
not enough to distort the diaphragm.
Rear
1. Insert push rod through non-pressure plate.
Place seal washer, seal washer spring, and dia-
phragm spring over push rod, then install push
plate on push rod. Tighten push plate firmly onto
push rod and stake in place.
2. Complete the assembly as directed in steps
2 and 3 under "Front."
SLACK ADJUSTERS
Slack adjusters function 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 at
front and rear brakes.
Internal construction of
both front and rear slack adjusters is as shown
in figure 11; however, lever arms (body) may be
offset or curved.
Slack adjuster consists basically of a hardened
steel gear, which is splined to the brake camshaft,
a brake lever (body), and a hardened steel worm
which is mounted in the lever above the gear and
meshes with the teeth in the gear. Turning the
worm shaft causes rotation of the camshaft in
relation to the brake lever. During brake opera-
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