A locking differential, differential lock, diff lock, air locker or locker is a variation on the standard automotive differential. A locking differential provides increased traction compared to a standard or “open” differential by restricting each of the two wheels on an axle to the same rotational speed without regard to available traction or differences in resistance seen at each wheel.
A diff lock is designed to overcome the chief limitation of a standard open differential by essentially “locking” both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel individually.
When the differential is unlocked (open differential), it allows each wheel to rotate at different speeds (such as when negotiating a turn), avoiding tire scuffing.
A diff lock forces both left and right wheels on the same axle to rotate at the same speed under nearly all circumstances, without regard to tractional differences seen at either wheel. A diff lock provides a significant traction advantage over an open differential, but only when the traction under each wheel differs significantly.