Spicer Tandem Drive Axles Service Manual D170, D190, and D590 Series - Manual (Page 87)

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Theory of Operation
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 transmission
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 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 following description assumes the system
includes a cab-mounted electric switch and a solenoid
valve as shown in the illustration. 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” position,
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 cylinder.
A compression spring moves the shift fork to disengage
the curvic clutch and unlock the wheel differential.
Theo
ry of Operation