Spicer Drive Axles Service Manual Axle Shift Systems, 2-Speed Single Rear Axles - Manual (Page 24)

21
Air Shift System
Troubleshooting
Check for Air Leaks
A simple method for quickly locating troubles in the system is
to listen for possible air leaks and for sound which would indi-
cate shift unit operation. Proceed as follows:
1. Turn ignition switch “ON” to energize and open sole-
noid valve. Move shifter knob to “HI”. In this posi-
tion, air pressure should be present in the entire
system. Check for air leaks.
2. With shifter knob in “LO”, air pressure should be
present only up to the shifter valve.
3. To check axle for shifting, operate shifter knob back
and forth from “LO” to “HI”. If the shift unit is oper-
ating, a definite reaction will be evident by sound of
parts movement.
4. If air pressure is satisfactory and shift unit does not
operate, disassemble and inspect shift unit.
Check Pressure Switch
In Low Range, the pressure switch is closed and electrical cir-
cuit is complete to the speedometer adapter. In High Range,
air pressure opens the pressure switch, and breaks the elec-
tric circuit to the speedometer adapter.
To check pressure switch operation, shift to High Range and
probe switch terminals. No voltage should be present.
Replace a faulty pressure switch as an assembly.
Check Electrical System
(with solenoid valve)
1. When ignition switch is “ON” solenoid valve is ener-
gized and air pressure is available to operate the sys-
tem. When ignition switch is “OFF”, solenoid valve is
de-energized and exhausts the system which down-
shifts axle to low range. Check wiring and circuit
breaker for defects that would cause shorts or open
circuits.
2. Make sure valve has a good ground connection to
the frame. With power at valve, check operation as
follows:
Disconnect lead wire and air line outlet at valve
and install air pressure gauge.
Apply power to valve and observe air gauge
reading. Operating pressure should be approxi-
mate reservoir pressure.
If gauge indicates approximate pressure, valve
is okay.
If gauge indicates low or no pressure, valve is
faulty. Replace valve assembly.
Check Quick Release Valve
The quick release valve provides a means of quickly exhaust-
ing air from system when axle is shifted from High to Low
Range.
To check valve operation, listen for audible air exhaust from
valve when shifting axle from High to Low Range. Replace a
faulty quick release valve as an assembly.
Check Speedometer Adapter
1. Make sure adapter is grounded to vehicle chassis.
2. Check wiring for shorts or grounds and trace electri-
cal circuit from ignition switch to speedometer
adapter.
3. Check for power supply at adapter terminal. With air
shifter valve in High Range, pressure switch is open
and power is not delivered to adapter. With shifter
valve in Low Range, the pressure switch is closed
and power is delivered to operate the speedometer
adapter. If power supply is okay, adapter is faulty.
Replace adapter assembly.