Spicer Single Drive Axles Service Manual: Single Reduction & Single Reduction with Differential Lock - Manual (Page 59)

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Theory of Operation
Ser
vice Procedure
Operate Wheel Differential Assembly
The Spicer Wheel Differential Lock is driver-controlled and
operated by a carrier mounted air-actuated shift unit. In
operation, it positively locks the wheel differential to provide
improved traction under adverse road conditions.
Control Systems for Differential Lock
Two systems may be used to control the differential lock
operation.
Transmission Low-Range Interlock Control System
The wheel differential is locked manually with the transmis-
sion in Low-Range. It is unlocked by the driver or unlocked
when the transmission is shifted out of Low-Range.
Note: The interlock system is preferred for vehicles equipped
with an air-shifted, Low-Range transmission. It is
designed to ensure the differential lock is not left
engaged (and to prevent accidental engagement) when
the transmission is in high range.
Direct Driver-controlled System
The driver manually locks and unlocks the wheel differential,
using a cab-mounted electric switch (or air valve). The follow-
ing description assumes the system includes a cab-mounted
electric switch and a solenoid valve as shown in the illustra-
tion. An air valve may be substituted for these components.
Operation is as follows:
1. With control switch in the “unlock” position, the
wheel differential functions normally.
2. When the control switch is placed in the “lock” posi-
tion, the air supply solenoid valve opens and air
pressure activates the shift cylinder. The shift fork is
moved to engage the curvic clutches, which, in turn,
lock the wheel differential.
3. When the control switch is placed in the “unlock”
position, air pressure supply to the shift cylinder is
shut off and air pressure is released from the cylin-
der. A compression spring moves the shift fork to
disengage the curvic clutch and unlock the wheel dif-
ferential.
1— Cab-mounted control valve (plunger in—valve open)
2— Dry air supply tank 80–120 PSI
3— Preferably equal in length
4— Power supply
5— Fuse or circuit breaker
6— Indicator light or audible signal
7— Wheel differential lock indicator switch (part of axle
assembly)
8— Rear axle wheel differential lock air shift cylinder (part
of axle assembly)
2
1
6 5
4
8
7
3