Drive Axles with Main Differential Lock

The main differential lock is a driver-controlled traction device operated from the vehicle cab. A dash switch controls the side to side lock-up of the rear axle, supplying equal traction to both sides. On tandem axles there are three possible differential lock options:

• Forward-rear carrier only

• Rear-rear carrier only

• Both rear carriers.

An indicator light comes on when the differential lock is engaged. An optional buzzer can also be used to indicate differential lock engagement.

The main differential lock provides maximum traction under slippery conditions. When the differential lock is engaged, the clutch collar completely locks the differential case, gearing, and axle shafts together, maximizing traction of both wheels and protecting against spinout. Under normal traction conditions, do not engage the differential lock. Operate the axle with differential action between both wheels.

Main Differential Lock Operation

To lock the main differential and obtain maximum traction under slippery conditions, move the control switch to the lock position.

If the vehicle is moving, maintain a constant vehicle speed while engaging the differential lock. Briefly let up on the accelerator to relieve torque on the gearing, allowing the differential to fully lock. The indicator light should come on and the buzzer should sound on vehicles so equipped. When the differential is fully locked, the turning radius will increase because the vehicle understeers. See Fig.. Drive cautiously and do not exceed 25 mph (40 km/h).

Turning Radius When Differential is Locked (engaged)—Understeer Condition

Turning Radius When Differential is Unlocked (disengaged)

Fig. 1, Turning Radius

To unlock the main differential, move the control switch to the unlock position. Briefly let up on the accelerator to relieve torque on the gearing, allowing the differential to fully unlock.

When the differential lock disengages, the indicator light will go off and the buzzer will stop.