GMC 4000 Series Service Manual page 141

Sec. 4A
Page 134
REAR AXLE A N D CONTROLS
Figure 12— Position of Drive Nut W hen Disassem bling
Figure 13— Rem oving Shaft, Actuating Lever, and Spring
Figure 14— R e m o v in g Drive Screw Bearing
G M C S E R V I C E M A N U A L
black ribbed wire is attached to bottom terminal.
Harness is clipped to cable clip on housing.
place, install shift unit over carrier studs. Make
certain that the swivel block of the shift fork ac­
tuating lever fits into the slot in carrier shift fork.
Tighten stud nuts firmly.
"Hi" range shift. Ignition or control switch must
be turned on before check can be made.
reversible and runs equally well in either direc­
tion. If the terminal wires are reversed, the unit
will shift to "Low" when the control switch button
is in "Hi" position, and will shift to "High" when
the button is in "Lo" position.
REMOVAL OF ROCKWELL SHIFT UNIT
Rockwell electric two-speed unit to remove it from
axle housing. This may be accomplished in the
following manner:
cover (25) (refer to fig. 18), then remove cover.
This also drains the lubricant. After cover is re­
moved, note that drive screw nut is either at top
or bottom (fig. 3) depending on whether axle is in
"HIGH" or "LOW" range position.
stud nuts (fig. 16) to remove preload from shift
unit spring.
way position on drive screw, sim ilar to figure 12.
This is necessary to prevent damage to drive nut
contact bumper.
torsion spring from push rod, then remove spring
and spring winding lever.
2. Install w ires to outside term inals. The long
3. With seal between carrier and shift unit in
4. Check installation by making a "Lo" and
NOTE: The shift unit motor is designed to be
It is necessary to partially disassem ble the
1. Remove five screws from shift unit housing
2. Loosen shift unit-to-differential carrier
3. Turn drive screw by hand to run nut to mid­
4. Pull out lever shaft (fig. 16). Disconnect
5. Remove shift unit-to-differential housing
Figure 15— Rem oving M otor W ires