Spicer Drive Axles Service Manual Axle Shift Systems, 2-Speed Single Rear Axles - Manual (Page 4)

1
Electric Shift System
Introduction
The service procedures and specifications in this publication
cover the current Spicer 2-Speed Axle Shift Systems.
Maintenance and overhaul instructions for the Spicer 2-Speed
Axle carriers are covered in the publications listed on the back
cover.
This manual includes information on two types of Shift Sys-
tems currently in use for Spicer 2-Speed Axles; Electric and
Air.
Spicer 2-Speed Axles are driver-controlled by means of a shift
unit operated from the vehicle cab. These shift units are acti-
vated by air or electric power depending on the convenient
source in the chassis.
Because of this variation, this publication is divided into two
major segments: Electric Shift System for hydraulic-brake
chassis and Air Shift System for air-brake chassis.
Electrical Operation
Note: For component identification and wiring schematic,
refer to illustrations on pages 1, 2, 3, and 4.
Unit in Low Range Shifting to High Range
Current flows through upper contact of control switch, closed
contacts of high-range switch, and motor to ground which
starts the motor rotating. Current also continues from com-
mon motor terminal through low-range switch and to ground
through the resistor.
When motor starts, rotation of the gear allows cam ramp to
apply pressure on low-range cam pin, which allows low range
switch to open. The path to ground (through resistor) is open
and the diode prevents speedometer adapter solenoid from
being energized.
Motor rotation continues to shift axle to high range. As shift is
completed, cam ramp of gear releases high-speed cam pin to
open high-range switch and creates an open circuit to turn off
power to motor. Motor rotation is stopped quickly by means
of dynamic braking through resistor.
If, during rotation, driver decides to switch back to low range,
motor continues to turn.
Opening of high-range switch has no effect since motor is
now being powered by the circuit from control switch,
through diode and low-range switch to ground at motor. In
this instance, motor continues to turn until cam pin opens
low-range switch to turn off power to motor.
Unit in High Range Shifting to Low Range
Current flows through control switch lower contact to ener-
gize speedometer adapter solenoid and through the diode and
low-range switch to common motor terminal and ground at
motor. Motor starts rotating. Current also flows through
closed contact of high-range switch and to ground through
resistor. Once gear rotates enough to apply cam pin pressure
on the high switch, circuit to ground through resistor is open.
As motor rotation continues to shift axle to low range, gear
rotates and releases cam pin on low-range switch to open
switch and open motor circuit. Motor power is turned off.
Once again, the resistor portion of the circuit provides braking
to stop motor quickly.
If, during motor rotation, driver decides to shift back to high
range, the motor continues to turn. Opening of low-range
switch has no effect since motor is now being powered
through control switch. In this instance, motor continues to
turn until gear rotation opens high-range switch to open
motor circuit.
The shift unit always remains synchronized with position of
driver's control switch.
ELECTRIC SHIFT UNIT CUTAWAY
Wiring Harness
and Connector
Black Wire
Green Wire
Red Wire
Worm Gear
Cam Pin
(High Range)
Slider
Block
Flat Washer
(0.100",
2.54 mm
thick)
Gear Pin
(Eccentric)
Gear
Switch
Spring
Cam Pin
(Low Range)
Circuit Board
Assembly
Motor