Chevrolet 30 Series 1967 Service Manual page 195

Maintenance and adjustments for the two-speed axle
are performed the same as those outlined for the Chev-
Service operations in this section are restricted to
those operations pertaining to items peculiar to the two-
speed axle only. For those operations common to both
An electric shift control is used on conjunction with the
Chevrolet 2-speed axles. The information necessary to
understand the construction, operation, maintenance, and
CONSTRUCTION
The electric shift control system is composed of the
manual control switch, speedometer adapter, axle shift
unit, circuit breaker, and connecting wiring or "harness"
(fig. 74).
MANUAL CONTROL SWITCH
The control switch, incorporated in the transmission
control lever (fig. 75), has two positions, up for high axle
range and down for low axle range. When the switch op­
erating knob is in either of these positions, a wiper con­
tact on the arm completes a circuit between the battery
and the motor in the axle shift unit (fig. 74).
To inspect or replace the control switch, disassemble
the transmission control lever knob by removing the
screw at top center of the knob, then lift off the knob top
half to expose the switch.
SPEEDOMETER ADAPTER
The speedometer adapter, installed behind the speed­
ometer, provides correct speedometer reading with the
axle in either high or low range. By introducing a gear
reduction into the speedometer drive upon shift to axle
low range, the unit compensates for the increased pro­
peller shaft speed relative to vehicle forward speed en­
countered in axle low range. When the axle is shifted to
high range, the speedometer drive is "straight thru" the
adapter.
The inner mechanism is prelubricated and sealed by
the manufacturer. In the event of failure, the adapter is
replaced as a unit.
AXLE SHIFT UNIT
The axle shift unit is mounted on the differential car­
rie r as shown in Figure 76. This unit contains a rev ers­
ible electric motor, which when energized, shifts the axle
into the desired range through the mechanism contained
in the unit (fig. 74).
MAINTENANCE AND ADJUSTMENTS
COMPONENT PARTS REPLACEMENT
ELECTRIC SHIFT SYSTEM
REAR SUSPENSION AND DRIVE LINE 4-37
rolet single-speed axles. Refer to "Rear Axle (Chevro-
let) Single-Speed."
the two-speed and single-speed axles, refer to applicable
procedure as outlined in "R ear Axle (Chevrolet) Single-
Speed."
repair of the electric shift mechanism is presented here
under self-explanatory headings,
WIRING SYSTEM
The power lead for the shift unit is connected to the
"cold" side of the ignition switch at the accessory term i­
nal, therefore, the entire system will be "dead" until the
ignition switch is turned to the "ON" position.
A thermal type circuit breaker installed on the front of
the dash panel provides protection in case of a short c ir­
cuit in the electric shift system during vehicle operation.
Should a short circuit occur the breaker will intermit­
tently de-energize the circuit until the trouble has been
corrected.
Three wires in the shift main harness (fig. 74) are
connected to the control switch. The red wire connects
the battery (thru the ignition switch and circuit breaker)
to the control switch. The white wire connects the con­
trol switch (thru the automatic switch) to one field of the
axle shift unit motor. The black lead connects the con­
trol switch (thru the automatic switch) to the other field
of the axle shift unit motor and also connects the speed­
ometer adapter.
OPERATION
The operation of the units in each speed range is ex­
plained in the following paragraphs.
HIGH SPEED RANGE
When the control switch operating arm is moved to the
up (HI) position, current is supplied to one field of the
motor in the axle shift unit. This current turns the a r­
mature and the drive screw in a clockwise direction and
moves the nut toward the bottom of the screw (fig. 77).
When the nut has traveled far enough to wind the
spring, a contact bumper on the nut breaks an electrical
connection on the automatic switch which de-energizes
the motor and stops armature rotation. The nut is held
at the end of its travel on the screw by a detent spring on
the shift housing front cover.
CHEVROLET TRUCK SERVICE M ANUAL