Understand Your Power Divider…

It was brought to my attention again this past week that most drivers don’t understand how a differential power divider functions. The Inter-Axle Differential (IAD), commonly referred to as the “Power Divider”, is by far the least understood component of a trucks powertrain.

The most common misunderstanding is that a truck is driven by only using one differential until the power divider is activated or “locked”, when in fact; a truck is driven by both differentials (all 4 wheels) on a tandem tractor whether the power divider is locked or unlocked. Another misunderstanding is that the power divider only operates when it is locked. However, the opposite is true; the power divider only operates when it is unlocked.

The power divider is a driver-controlled, air-actuated traction device that when operated in the unlocked position allows for speed differences between the forward and rear tandem drive shafts while providing equal pulling power from each axle of the tandem. With the power divider unlocked, a tandem axle truck can completely lose traction by spinning one wheel on either axle. Locking the IAD switch on the vehicle dash, improves traction by locking the front and rear drive shafts together, forcing one wheel on the front axle and one wheel on the back axle to spinout before the truck loses traction.

Here are a few “Tips” for proper IAD operation.
• The IAD switch should be in the “Unlock” position for normal operating conditions where there is good traction.
• “Lock” the IAD at any speed when approaching or anticipating icy or poor driving conditions to provide improved traction.
• Always unlock the IAD when the need for improved traction has passed or when the vehicle is on a good road or highway.
• After locking or unlocking the IAD, let up on the accelerator to provide an interruption in torque to the drivetrain. Activating the IAD lock is similar to shifting a manual transmission with a clutch.
• Do not actuate the IAD switch while one or more wheels are actually slipping, spinning or losing traction, or damage to the axle can result.
• Do not spin the wheels with the IAD unlocked, or damage to the power divider could result.

I hope this helps you to understand how your power divider works and how to use it.

Ken Cooke
Coastline Transmission