GMC 4000 Series Service Manual page 394

DRIVE BELT M AINTENANCE
A N D ADJUSTMENT
Drive belts used on models covered by this
manual are made of neoprene rubber with polyester
cord.
MAINTENANCE
Drive belt must be kept at proper tension. A
loose belt will lower output of com pressor, while
a tight belt will cause eventual bearing failure. A
regular, periodic inspection is recommended to
check condition and tension of drive belt. Replace
belt if frayed or badly worn.
ADJUSTM ENT
1. Loosen bolt at adjusting arm. Loosen pivot
bolt at com pressor mounting bracket.
2. Position com pressor so that a reading of
120-130 lbs. (new belt) or 80-90 lbs. (used belt)
is obtained on a strand tension gauge.
3. Tighten adjusting arm bolt and/or nut s e ­
curely. Tighten pivot bolt nut.
NOTE: On a new vehicle, or after a new belt
is installed, check belt tension once in first 200
m iles of operation.
COMPRESSOR REPLACEMENT
REMOVAL
1. Exhaust com pressed air from air system .
2. Disconnect air and oil lines from com­
p ressor.
3. Loosen pivot bolt at com pressor base, then
loosen com pressor adjusting arm bolt. Tilt com­
pressor and remove drive belt from compressor
pulley.
4. Disconnect adjusting arm from compressor
by removing adjusting arm bolt.
5. Remove bolts attaching compressor crank­
case to mounting bracket. Lift air com pressor a s­
sembly off mounting bracket.
INSTALLATION
1. Clean oil supply line to com pressor and if
possible, run engine a few seconds to be sure oil
supply to compressor is flowing freely.
2. Clean oil return line or passage through
com pressor mounting bracket to be sure oil from
com pressor crankcase can return to engine crank­
case.
3. Lubricate compressor cylinder walls and
bearings with lubricating oil before placing com­
pressor in position.
4. Clean or replace any damaged or dirty air
lines which may be corroded before connecting
them to the com pressor.
G M C S E R V I C E M A N U A L
AIR COMPRESSORS A N D GOVERNORS
faces of com pressor crankcase and mounting brac­
ket are clean. Position com pressor on mounting
bracket and attach with bolts. Connect com pressor
adjusting arm to bracket on side of com pressor
cylinder head or block. Do not tighten.
Check all connections for tightness.
adjust belt tension as previously directed.
inghouse and Midland-Ross com pressors can be
replaced without removing compressor from the
vehicle. Since the unloader assem blies differ by
manufacturer, a separate procedure is given for
each assembly.
BENDIX-WESTINGHOUSE
loader assembly. Unloader parts (fig. 3) may be
changed without removing cylinder head as follows:
Removal (Fig. 4)
spring and raise spring off unloader spring saddle.
Remove spring and spring saddle.
and plunger. Lift pistons out of bores. If piston is
Figure 3 — U n lo a d e r A s s e m b ly C o m p o n e n ts (B -W )
5. Use new gasket and make sure mating sur­
6. Connect air and oil lines to com pressor.
7. Place drive belt in compressor pulley and
8. Adjust governor as directed later.
UNLOADER ASSEMBLY
REPLACEMENT
Unloader assem blies on both Bendix-West-
Parts are available in a kit for replacing un­
1. Remove air inlet elbow and discard gasket.
2. Insert screwdriver blade under unloader
3. Lift each plunger guide and remove guide
Sec. 6T
Page 383
Piston