GMC 4000 Series Service Manual page 395

Sec. 6T
Page 384
AIR COMPRESSORS A N D GOVERNORS
REMOVING OR REPLACING
UNLOADER SPRING
not easily removed, build up air pressure in sy s­
tem until governor cuts out, raising piston. If com­
p ressor has been removed from vehicle, use air
pressure as shown in figure 4.
Installation (Fig. 5)
1. Carefully insert each piston, complete with
O-ring and back-up ring, in bore.
2. Slide plunger guide down over unloader
plunger. Place each guide and plunger in position
above unloader piston, then push guide down over
top of piston.
3. Install unloader spring and spring saddle.
Make sure saddle rests squarely on top of plunger
guides, and make sure top of spring engages spring
seat in cylinder block.
4. Install new gasket at air inlet and connect
air inlet elbow.
INSTALLING UNLOADER
PISTON
G M C S E R V I C E M A N U A L
REMOVING UNLOADER
PISTON
Figure 4 — R e m o v in g U n lo a d e r C o m p o n e n ts (B -W )
MIDLAND-ROSS
a new unloader installed in its place, omit the un­
necessary steps.
Removal and Disassembly (Fig. 6)
ernor and unloader. Remove tube assembly.
sembly to cylinder head.
valve plunger and plunger spring.
expander spring from body. Should difficulty be
encountered in removing these parts, apply air
pressure to body to force out these parts.
INSTALLING GUIDE AND PLUNGER
ON UNLOADER PISTON
Figure 5 — Installing U nloader Com ponents (B-W )
REMOVING UNLOADER PISTONS
U6ING AIR PRESSURE
If a defective unloader is being removed and
1. Disconnect both ends of tube between gov­
2. Remove two bolts attaching unloader a s­
3. Remove unloader assem bly. Remove inlet
4. Remove bushing, valve, diaphragm, and
5. Remove rubber retainer from bushing.
INSTALLING UNLOADER
SPRING AND SADDLE