Spicer Convertible Tandem Axles - Manual (Page 65)

59
Theor
y of Operation
Theory of Operation
Operate Wheel Differential Assembly
The Spicer wheel differential lock is driver-controlled and oper-
ated 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 oper-
ation.
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
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.