Operation
When highway conditions improve (good traction), the PDL
should be disengaged, again at a low, even speed. Letting
up on the accelerator momentarily will unlock the interaxle
differential.
Tandem axle power dividers or interaxle differentials
in the forward rear axle are controlled by the
dash-mounted power divider lock (PDL LOCK)
switch.
The switch indicator will turn on when the PDL is
engaged (locked). The vehicle may be electronically
programmed to provide an alarm when a speed is
reached where it is not appropriate to have the power divider
locked. In this event, an alarm will sound (5 beeps) and the
switch indicator will flash slowly (once per second). A fast
flashing (twice per second) switch indicator signifies a problem
in the PDL system.
Under normal highway conditions (good traction), the PDL
should be disengaged, which allows differential action between
the forward rear axle and the back rear axle, preventing interaxle
differential wear due to unequally worn or mismatched tires, etc.
Driver-Controlled Differential Lock
The differential lock feature locks together the axle’s
left and right axle shafts for improved traction on
reduced traction surfaces.
Some vehicles are equipped with this optional
driver-controlled differential lock feature (DIFF LOCK).
The air-actuated traction device can be manually
shifted from the vehicle cab. By actuating a switch,
mounted on the instrument panel gauge cluster, the driver can
lock or unlock the rear axle differential(s) when the vehicle is
moving or stopped.
Other vehicles with tandem rear axles
(6X4) are equipped with two optional
driver-controlled differential lock features
(DIFF FR AXLE/LOCK and DIFF RR
AXLE/LOCK). The air-actuated traction
devices can be manually shifted from the
vehicle cab. By actuating the switches,
mounted on the instrument panel gauge cluster, the driver can
independently lock or unlock the forward-rear and/or rear-rear
axle differentials when the vehicle is moving or stopped.
When the differential is fully locked, the vehicle will have a slight
understeer condition. This will increase the turning radius of the
vehicle.
On vehicles with multiple drive axles, the differential lock can be
used in conjunction with the Power Divider Lock (PDL) to achieve
maximum available traction in adverse road surface conditions.
To limit stress on the axle and tires during vehicle turning
maneuvers and improve stability, the use of the differential lock
must be limited to low vehicle speeds, under 25 mph (40 km/h).
Also, to maintain vehicle stability, the differential must not be
locked when the vehicle is traveling down steep grades and
traction is minimal. DIFF LOCK will automatically disengage
when vehicle speeds exceed approximately 25 mph (40 km/h).
Do not engage the locking differential when the tires are
spinning.
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