What is PDL Lock? How Does PDL Lock Work?

Written by

Charles Bolte


Vernon Hoppe 

what is pdl lock

The inter-axle differential (IAD), also referred to as the “power divider lock,” or what is PDL lock commonly known as, is a drivetrain component that helps to distribute power between multiple axles when one axle may have less traction than the other, such as when driving on uneven or slippery terrain.

It allows power to be transmitted to both axles while allowing them to rotate at different speeds in vehicles with multiple drive axles, such as trucks and heavy-duty vehicles.

Function of PDL

The Power Divider Lock (PDL) expertly regulates wheel power distribution during inclement weather and on muddy or slippery roads.

PDL selectively transmits more power to the wheels that maintain grip while reducing the spinning force of others. Locking them in ensures that regardless of traction loss, each axle runs at the same speed.

They also facilitate cornering by allowing wheels on opposite ends to run at different speeds.

How Does PDL Lock Work?


PDL mechanism works by utilizing “in or out” mode, it ensures optimal acceleration during shifts within various ranges by evenly allocating power between the two axles.

More force goes towards powering up the front axle in “in” mode. At the same time, energy is diverted mainly to the rear axle depending on weight distribution and terrain type on “out mode”.

Engaging Power Divider Lock

1. When to use PDL

The PDL should be engaged to prevent inter-axle differential action in the following situations:

  • Cacking up a tractor under a trailer
  • Starting on a slick surface
  • Operating off-road in muddy conditions
  • Traveling on slick highways

PDL must be engaged only when the vehicle is completely stopped or moving at low speeds.

Attempting to engage the PDL while the wheels are already spinning may result in severe damage to the power divider components and unexpected vehicle shocks.

2. When NOT to use PDL

  • When traversing a dry pavement with good traction, avoid activating PDL. This is because doing so can cause excessive wear on the tires and axles, which can lead to premature failure of these components.
  • Never engage PDL when the wheels are spinning. This can cause the vehicle to lose control and potentially result in an accident.

How to Activate and Deactivate

Knowing how and when to operate power dividers in your truck is crucial to navigating situations such as icy highways or muddy fields, safely and efficiently.

Follow these steps to activate the power divider, if you find yourself struggling with traction:

  • Release the accelerator pedal and check that the truck is traveling straight.
  • Toggle the power divider switch to lock PDL, which is usually found on the dashboard.
  • Continue driving normally after depressing the accelerator pedal.

To deactivate the power divider, perform the following steps:

  1. Drive in a straight line and let go of the gas pedal.
  2. To disengage the mechanism, press the power divider switch.
  3. To resume normal driving, depress the accelerator pedal.

PDL Lock vs. Diff Lock


Ensuring maximum traction when traversing treacherous landscapes is essential for trucks, and two key mechanisms make this possible: the PDL lock and differential locks.

When configured in tandem, the PDL connects front and rear axles, while differential locks ensure both wheels rotate at the same speed even without traction.

This ensures that every bit of available torque is utilized effectively, resulting in exceptional grip on even the most challenging terrains.

Frequently Ask Questions


Is there a PDL on a semi-truck?

An individual and exclusive PDL lock on semi truck exists in the rear section of a semi-truck, placed between two differential boxes.

It is critical to recognize that modern-day semis are equipped with power divider locks. This feature improves traction and stabilizes performance when transporting heavy loads.

What is the function of differential lock on semi trucks?

It is essential for a semi-truck to maintain control and stability while on the road, which makes the function of semi-truck differential lockers, crucial.

The system operates by locking two wheels together, providing heightened traction in situations where it becomes necessary. Ultimately, this ensures energy waste reduction and fuel efficiency improvement.

Difference between Off-road switch vs PDL lock

By disabling the off-road switch, drivers gain increased power delivery capability while maintaining full throttle response when needed most.

On the other hand, PDL locks provide excellent grip by locking both axles together firmly for maximum torque distribution during low-traction scenarios like mud bogs or rock climbs where extra force is required to move forward successfully.

What is a power divider on a truck?

The power divider is one such air-actuated traction device controlled by drivers, which plays an indispensable role in tandem axle truck stability and performance maintenance.

Indicators of PDL in International Prostar?

The International Prostar PDL lock works by securing the inter-axle differential, allowing both rear wheels to turn at equal speeds regardless of which has better traction.

The PDL lock switch on international trucks is controlled on the dashboard which shows engagement or lock status. The international PDL light flashing confirms whether PDL is active or inactive.


Understanding what is PDL lock and how to use and maneuver its system improves driver safety when navigating slippery highway conditions, primarily under adverse weather conditions where low visibility may affect the smooth operation.

As technology advances, manufacturers must improve warning systems that alert drivers to unsafe speed levels with locked power dividers. As we strive for safer driving experiences, including such features will increase driver safety on our roads.

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