GMC 4000 Series Service Manual page 144

Drive Screw
The drive screw assembly is serviced only
as an assembly. While holding the nut, rotate the
screw from one end to the other. It should rotate
freely. When the nut gets to either end of the screw,
the screw should continue to turn, but the nut should
not jam or run off the ends.
Electric Motor
The motor (serviced only as an assembly) is
reversible. With the motor housing connected to
one battery terminal, and either one of the two
motor w ires connected to the other battery term ­
inal the motor will run in one direction. With the
other motor wire connected to the battery, motor
will run in the opposite direction.
The motor has a stall torque of approximately
6 inch-pounds. Clamp a small crescent wrench on
the rectangular drive on the armature shaft. Place
motor in vise, and grasp wrench handle with one
hand. Connect one motor wire to a battery terminal
and connect motor housing to the other battery
terminal. The wrench should tend to turn with a
torque of about 6 inch-pounds. Allow wrench to
turn VERY SLOWLY, making sure that this pull or
torque is present the FULL 360 degrees turn of
the wrench. If one armature is burned out, the
torque will disappear for a small part of the 360
degrees. Do not overheat the motor while making
test. Motor must be replaced as an assembly, and
is lubricated for life of motor. The motor used is
12-volt type which is the same as truck electrical
system . When installing a new motor use care to
select motor of proper voltage. Voltage is stamped
on motor housing and on side cover of shift unit.
Miscellaneous Parts
Gaskets should be replaced at assembly.
Inspect bearing. If balls are rough or chipped,
replace with new bearing and snap ring assembly.
Pack bearing assembly with clean grease (Chassis
Grease) - Symbol "C" in LUBRICATION (SEC. 0).
Inspect torsion spring (23, fig. 11 and 18) for
breaks or wear at lever contact points. Make ce r­
tain that correct replacement spring is used.
ASSEMBLY (EATON AND CORP.)
Key numbers in text refer to figure 11.
1. Install automatic switch assembly (17) into
housing. Use flat head screw (18) to attach switch
to housing. On outside of housing, install two bush­
ings (11), fiber washers (10), and jam nuts (9) over
switch terminal screw s. Tighten nuts firmly.
2. Install motor assembly grommet (7), then
install gasket (5) on housing. Install motor (6) and
cover (4) into housing. Install three screws and
lock washers (1) and two stop nuts (2). Install
motor cover cable clip (3) under outer screw.
Tighten screws and nuts firmly.
G M C S E R V I C E M A N U A L
The red or longer wire attaches to bottom term ­
inal. Tighten inside terminal nuts (19) firm ly.
drive screw (20), install bearing (12) on end of
screw with shielded side of bearing toward inside.
Retain bearing with bearing lock nut (13).
slotted end of screw into housing, meshing slotted
end with armature shaft.
must be toward switch.
screw s and lock washers (16). Tighten screws
firm ly.
tuating lever (22), torsion spring (23), and spring
winding lever (24) has been separated, reassem ble.
With shift fork actuating lever (22) in vise, assem ­
ble parts as shown in figure 21. Turn the spring
REAR AXLE A N D CONTROLS
Figure 19— Rem oving Torsion Spring (Rockwell)
3. Attach motor w ires to switch terminals.
4. With a screwdriver inserted into slot of
5. Run nut to center of screw, then insert
NOTE: Fiber bumper contacts on drive nut
6. Install gasket (14) and cover (15) with three
7. If the assembly consisting of shift fork ac­
Figure 2 0 — R e m ovin g Torsion Spring (Rockwell)
Sec. 4A
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