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GM COACH MAINTENANCE MANUAL
Sec. 4
Page 51
phragm seat on top of body.
If
damaged in any
way, replace body.
Inspect diaphragm follower
seat for excessive wear or damage. Replace body
if worn excessively or damaged.
Inspect small
bleed hole leading from outlet port to diaphragm
cavity to make sure
it
is not restricted.
Inlet and Exhaust Valve Assembly
Inspect inlet and exhaust valve assembly for
broken spring and worn or damaged valves and
seat.
If
damaged or worn excessively, replace.
REPAffi (Fig. 7)
The following procedure covers disassembly
and assembly of the diaphragm, plunger, and spring
cage assembly for replacement of the diaphragm
or exhaust valve seat.
Disassembly
1. Remove valve cap from spring cage, holding
spring cage with a strap wrench or by using a
special tool in steps at bottom of cage.
Be sure
not to score or damage the spring cage.
2. Remove nut from top of plunger, holding
the plunger with a rod inserted through the ex-
haust holes in the plunger.
Remove flat washer
and shims from top of plunger. Lift spring cage,
pressure regulating spring, and shims off plunger
and diaphragm assembly. Be sure and keep shims
intact for reuse at assembly.
3. Remove snap ring from plunger above dia-
phragm and lift off diaphragm assembly.
Exhaust Valve Seat Replacement
Pull exhaust valve seat from lower end of
plunger.
Press new seat into plunger and ream
to .515" plus or minus .002".
Edge of seat must
be sharp and true to form a perfect air seal.
Assembly
1. Place new grommet in diaphragm assembly,
then place diaphragm assembly over small end of
plunger. Install snap ring on plunger to hold dia-
phragm in place.
2. Place pressure regulating spring shims on
diaphragm plate, being sure the same shims that
were removed are used.
3. Place pressure regulating spring and spring
cage on diaphragm and plunger. Compress pres-
sure regulating spring and install shims, washer,
and nut on top of plunger.
Make sure the same
shims that were removed are used.
Tighten nut
firmly and stake in place.
4.
Thread valve cap into top of spring cage,
tighten firmly and stake in place.
APPLICATION VALVE ASSEMBLY (Fig. 7)
1. Place lower valve body on bench, bottom
side up. Drop inlet valve shims into valve opening
AIR BRAKES
in bottom of body, being sure the same shims that
were removed are used. Place inlet valve assem-
bly in body, with the valve guide inserted in the
bore in body.
2.
Place new inlet valve body grommet in
body on top of inlet valve seat, then install inlet
valve body. Install lock washers and nuts on inlet
valve body studs and tighten firmly.
3. Turn lower body over and place diaphragm
return spring in body.
4. Install new grommets
in
grooves in plunger
and upper body. Coat surface of spring cage and
plunger lightly with petroleum jelly, then insert
spring cage into upper body and align opening in
diaphragm with opening in body.
5. Place upper body and diaphragm assembly
on lower body with the lower end of the plunger
inserted in bore in lower body and with the ex-
haust opening in diaphragm aligned with exhaust
opening in lower body.
6. Align bolt holes in upper body, diaphragm,
and lower body, and install six body bolts.
Make
sure the three long bolts are installed in the cor-
rect holes as marked on lower body prior to dis-
assembly. Install lock washers and nuts on bolts
and tighten firmly.
7. Install rubber boot on top of valve assem-
bly, making sure edges of boot are properly seated
in grooves in valve cap and upper body.
Press
down on valve cap several times to make sure the
spring cage slides freely in upper body.
TEST AND ADJUSTMENT OF
REBUILT APPLICATION VALVE (Fig. 7)
Tests
Install rebuilt application valve in vehicle and
test as previously directed under "Serviceability
Tests" in this section.
If
valve does not meet re-
quirements given in "Operating Test," make ad-
justments described below.
If
valve does not pass
the "Leakage Test," valve must be removed and
leakage corrected.
Adjustments
1.
If
the valve does not release promptly, or
does not fully release, it indicates that the exhaust
valve is not opening sufficiently.
This can be
caused by:
a. Improper adjustment of treadle adjusting
screw, causing roller to exert too much force on
valve cap when treadle is released.
b. Insufficient shims between inlet valve
seat and body of brake valve.
2. If the brake valve does not apply promptly,
or does not fully apply, it indicates that the inlet
valve is not opening sufficiently.
This can be
caused by:
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