All About Locking Differentials

The Difference Between Open And Locked Diffs

ARB, Air Locking Rear Differential
ARB, Air Locking Rear Differential. (Richard Harvey/Wikimedia Commons/CC ASA 3.0U)

When it comes to traction in off-road situations, differentials play a key role. Compared to a standard or open differential, a locking differential (also known as a diff lock, locker or differential lock) adds more traction. These are common in four-wheel drive (4WD) vehicles. 

The locking differential limits the two wheels on an axle to rotate at the same speed. In essence, it locks them together as a unified shaft. Both wheels then turn together, regardless of the traction that may or may not ​be available. With a locked differential, each wheel can apply as much spinning force as the traction will allow. This means the torques on each side will be unequal but have equal rotational speeds. 

On the other hand, an unlocked, standard or open differential means that each wheel can rotate at different speeds. This occurs when you turn and prevents tire scuffing. An open differential provides the same torque to each of the wheels on a single action. Even though the wheels can spin at different speeds with this type of differential, they receive the same force for the rotation -- even if one is stationary and the other is moving. This means that each wheel receives equal torque despite having an unequal rotation speed.

Automobiles that have standard four-wheel-drive, also known as all-wheel drive, possess three differentials. There is one differential on each of the two axles, and a central differential between the front and rear axles (known as a transfer case).

Vehicles with a locked differential may be at a bigger advantage when it comes to traction compared to a vehicle with a standard or open differential, but only when the traction under each wheel is different. If you are a serious off-road driver, your vehicle probably has a locking differential. 

Types of Locking Differentials

There are three main types of locking differentials:

  • An automatic lock will lock and unlock automatically; the driver does not have to do anything in this case. These make sure that the right amount of power always flows to both wheels regardless of how the traction is. They will then unlock when one wheel needs to spin faster when turning on a corner. At rest, the position says locked. This type of differential increases wear on the tires.
  • A selectable lock puts the driver in control of turning the differential into the lock and unlock modes. It can use either pneumatics (compressed air), electronic solenoids (electromagnetics) or a cable-operated mechanism to operate. They are more complex and expensive compared to automatic locks. This type lets the differential perform in open mode for better drivability and maneuverability, but there are more parts involved that can fail.
  • Spools are devices that connect the axles and are not featured in most consumer cars -- only competitive driving vehicles.

It may sound like having a locking differential is the best option, but there are some disadvantages to them. Again, there is more tire wear because they do not operate as smoothly as a standard or open differential. They can create banging or clicking noises during the locking and unlocking process. If you are serious about off-roading, however, they may be just what you need.