Locking the Differentials and Improving Traction

locking the differentials and improving traction

We all think we know how to cope in low traction situations, but how much do we really know how to go about locking the differentials and improving traction? The team at Meritor have come up with some straight forward guidance to avoid confusion.

First of all when looking at using different locking techniques to overcome poor traction conditions, we need to understand just what is built into the differentials in the drive axles.

When the truck is in a low traction situation, there is a danger either of the wheel ends may lose traction, causing spinout and damage to differential components. There are two components designed to overcome this issue and keep the truck moving, the DCDL and the IAD.

The Driver Controlled Differential Lock (DCDL) locks the main differential allowing equal torque applied to both driving wheel ends on the same axle assembly. The lock position maximises traction to both wheels on the same driving axle and protects against spinout damage to the main differential.

Activating the DCDL:

1. Driving on a good traction surface, without the wheels spinning at different speeds to each other, slipping or losing traction, flip the DCDL control switch to the ‘LOCK’ position while maintaining a constant vehicle speed under 40km/h. Prior to driving on unfavourable road conditions.

2. Let up momentarily on the accelerator to relieve torque on the gearing, allowing the DCDL to lock.

3. When the DCDL is activated, the indicator light will be on and there may also be an

audible signal.

4. When the DCDL is fully locked, the vehicle will have an ‘understeer’ condition when making turns. Proceed cautiously over poor road or highway conditions, NEVER exceed 40 km/h, and use good driving judgment.

To de-activate the DCDL:

1. Once you are back onto a good traction surface, flip the DCDL control switch to the ‘UN-LOCK’ position while maintaining a constant vehicle speed under 40km/h.

2. Let up momentarily on the accelerator to relieve torque on the gearing, allowing the DCDL to Un-lock.

3. When the DCDL is de-activated, the indicator light will be off and or the audible signal will switch off.

An Inter-Axle Differential (IAD) works in a similar manner to the main differential except it splits the torque equally between the two axles (hence the common reference to ‘Power Divider’) of a tandem, rather than the two wheel ends of an axle. The IAD Lock can be applied at any safe speed (assuming both axles are rolling and that spinout has not started to occur) and/or remain engaged for long periods of time at any safe speed depending on road and weather conditions.

Activating the IAD:

1. Maintain vehicle speed while on good a traction surface.

2. Flip the IAD switch to the ‘LOCK’ position then let up momentarily on the accelerator to relieve torque on the gearing.

3. The inter-axle differential lock will engage. Proceed to drive cautiously.

To De-Activate the IAD:

1. Maintain vehicle speed while on good a traction surface.

2. Flip the IAD switch to the ‘UN-LOCK’ position then let up momentarily on the accelerator to relieve torque on the gearing.

3. The inter-axle differential lock will diss-engage. Proceed to drive cautiously.

SUBHEAD///Using the DCDL and IAD at the same time

The DCDL works in conjunction with the IAD Lock to provide maximum possible traction when the vehicle requires it. The IAD Lock ensures there is maximum traction potential for both the forward and rear drive axles of the tandem. Locking the DCDL on each axle ensures maximum traction at each wheel end of each side.

When approaching poor traction conditions, first engage the IAD switch. As conditions worsen and when vehicle travel speed is 40 km/h or less, the DCDL lock can then be engaged for added traction

When the DCDL is locked, the vehicle’s turning radius will increase. This condition is called ‘understeer’. The driver must use caution, good judgment and drive at low speeds when operating the vehicle with the DCDL locked.

It is recommended that in a tandem drive axle the IAD is in the lock position prior to engaging the DCDL.

locking the differentials and improving traction