Chevrolet 10 Series 1968, Service Manual

Page: 207 / 713

REAR SUSPENSION AND DRIVE LINE 4-38
which pivots on a pin in the nut, winds the torsion spring.
Thus the tension of the spring is increased, and in this
position, the axle is ready to shift into the high speed
ratio as soon as the load on the axle gears is relieved.
The torsion spring is assembled in the unit so that it is
under 65 pounds pressure. When the spring is wound by
the winding lever, this tension is increased to 115 pounds.
This additional pressure is used to shift the axle. When
the shift is completed, the ends of the spring come to­
gether, leaving the original tension in the spring. This
preload tension holds the axle in either range.
Low Speed Range
When the control switch operating arm is moved to the
down (LO) position, current is supplied to the other field
of the motor and to the speedometer adapter. The cur­
rent now causes the armature and screw to turn counter­
clockwise, and the nut travels toward the top of the screw
(fig. 77). This winds the torsion spring for a shift to low
range which is accomplished in the same manner as the
shift to high range.
General Maintenance
The only general maintenance necessary on the shift
control system is to make sure that all wiring is in good
condition, with connections tight at terminals, connectors,
and that the axle shift unit is filled with lubricant to
proper level.
The shift unit should be filled with lubricant to the
fille r opening on the front cover using SAE 10 engine oil.
At ambient temperatures below 0°F use SAE 5W. The oil
level should be checked every 10,000 miles or 3 months,
whichever occurs first.
Shift Unit Service
Rem oval
1. Disconnect one of the battery cables.
2. Remove two shift housing to carrier stud nuts and
lock washer (fig. 75).
3. Remove shift unit assembly from carrier (fig. 78).
Check condition of rubber seal assembly between
shift unit and carrier. This seal must be in good
Fig . 79—Shift Unit Drive Nut Position for Disassembly
condition and be held tightly to the shift yoke by the
spring clamp to prevent axle lubricant from leaking
into shift unit.
4. Disconnect wire at plug.
Disassem bly
Key numbers in text refer to Figure 73.
1. Remove six screws (22) and lock washers which at­
tach cover (20) to shift motor housing (5). Drain
lubricant from housing. Remove gasket (19).
2. After removing cover, the drive screw nut (25) will
be at either top or bottom depending upon the posi­
tion in which the control switch was left.
Fig . 78—Sh ift Unit Removed from C a rrier F ig. 80—Removing Shaft, A ctuating Lever and Spring
CHEVROLET TRUCK SERVICE MANUAL