Drive Axle Feature Operation

Differential Lock

The driver-controlled differential lock feature (side-to-side wheel lock, traction control, or traction equalizer) provides maximum traction for slippery conditions by forcing the wheels on each drive axle governed by the switch to rotate together. When the differential lock is engaged, the clutch collar completely locks the differential case, gearing, and axle shafts together, maximizing the traction of both wheels.

Differential Lock Switches

There are several differential lock options available:
a switch to control the differential lock on the forward drive axle.
a switch to control the differential lock on the middle drive axle.
a switch to control the differential lock on the rearmost drive axle (see Fig. 16.1 , Item 3).
  • 1. Interaxle Lock Switch
  • 2. Fifth Wheel Slide Switch
  • 3. Rearmost Axle Differential Lock Switch
  • 4. Air Suspension Dump Control Switch
Fig. 16.1, Axle and Suspension Switches

Differential Lock Operation

NOTE: On some vehicles, the differential lock system is connected through the low speed range of the transmission. If this system is used, the transmission must be in the low speed range for the wheels to fully lock. In addition, shifting out of low speed range will also disengage the differential lock.
WARNING
Locking the wheels when the vehicle is traveling down steep grades or when the wheels are slipping could damage the differential and/or lead to loss of vehicle control, causing personal injury and property damage.
NOTICE
Engage the differential lock only when the vehicle is stopped or moving at less than 5 mph (8 km/h). Engaging the differential lock at high speeds can cause internal axle damage.
1.
With the engine running, move the differential lock switch to LOCK to engage the differential lock.
2.
If the vehicle is moving, briefly let up on the accelerator to relieve torque on the gearing, allowing the differential to fully lock.
WARNING
Be especially careful when driving under slippery conditions with the differential locked. Though forward traction is improved, the vehicle can still slip sideways, causing possible loss of vehicle control, personal injury, and property damage.
3.
Drive cautiously and do not exceed 25 mph (40 km/h). When the differential is fully locked, the turning radius will increase because the vehicle understeers. See Fig. 16.2 .
  • A. Turning Radius When the Differential Lock is Engaged (understeer condition)
  • B. Turning Radius When the Differential Lock is Disengaged
Fig. 16.2, Turning Radii
4.
Move the differential lock switch to UNLOCK to disengage the differential lock after leaving poor road conditions.
NOTE: If the differential lock is engaged when the engine is shut down, the differential lock will disengage.
5.
If the vehicle is moving, briefly let up on the accelerator to allow the wheels to fully unlock, then resume driving at normal speed.

Interaxle Lock

The interaxle lock (axle lock, interaxle differential lockout) feature is available on vehicles wth tandem- or tridem-drive axles. The interaxle lock causes the drive axle shafts to rotate together, and is recommended for use under adverse road conditions where greater traction is needed. Do not wait until traction is lost and the tires are spinning before engaging the interaxle lock.
See the axle manufacturer's website for more information.
When engaged, the interaxle lock essentially makes the driveshaft a solid connection between the drive axles. Power entering the forward drive axle is transmitted straight through to the rearmost axle(s). Driveline torque is now delivered equally and the drive axles, and wheels, turn together at the same speed. The interaxle lock increases drivetrain and tire wear and should be used only when improved traction is required.

Interaxle Lock Switch

The interaxle lock switch allows the driver to lock the drive axles together. See Fig. 16.1 , Item 1.

Interaxle Lock Operation

NOTICE
The interaxle lock should not be engaged on a vehicle with obviously spinning wheels. Engagement at high speed or power can damage the axle(s).
1.
With the engine running, move the interaxle lock switch to LOCK to engage the interaxle lock.
2.
If the vehicle is moving, briefly let up on the accelerator until the interaxle lock engages.
NOTICE
Do not operate the vehicle continuously with the interaxle locked during extended good road conditions. To do so could result in damage to the axle gearing and excessive driveline and tire wear.
3.
Proceed over poor road conditions with caution.
4.
Move the interaxle lock switch to UNLOCK to disengage the interaxle lock after leaving poor road conditions.
5.
If the vehicle is moving, briefly let up on the accelerator to allow the interaxle lock to disengage, then resume driving at normal speed. Once the interaxle lock disengages, the indicator light will go off.