How Does a Power Divider on a Semi Work?

by Robert Morello
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Truck image by JASON WINTER from

The semi or tractor-trailer truck engine and drivetrain are complicated mechanical systems designed to create the most pulling power. The power divider is common on large trucks and aims to provide better traction for the driver in certain situations.

Power Divider Function

The power divider is a separate differential box located between the already existing two differential boxes at the rear end of the truck. This differential can be locked and unlocked by the driver in situations when there is little or no traction for the drive wheels. When engaged, the power divider delivers more power to the wheels that have grip and less or none to those that are slipping.

Power Divider Effects

When engaged, the power divider locks the gearing between the first and second differentials into place, thus creating a rigid power train system and more directed power. The power divider is similar in effect to a locking differential or a traction control system you might see in a passenger car.


The power divider must be operated manually and only in times of low traction. To leave the power divider engaged full-time would result in broken axles, shredded gears or broken seals at the wheel points. Due to the extremely heavy loads carried by semis, the power divider, engine break and spike are essential tools to provide proper control for drivers.

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