Diff Lockers Explained


An open differential is designed to permit both wheels to rotate at different speeds, allowing the vehicle to turn properly.  This works fine when you have good grip, but in low-traction scenarios this can pose a problem.  With one wheel spinning faster than the others, this can cause the wheel to ‘dig in’ and make the situation worse.

The most simple solution would be to weld the differential ‘closed’, so that both wheels turn at exactly the same rate.  Whilst this is beneficial in a straight line, this has major drawbacks when turning corners – both on and off road.

Air Lockers

ARB is the leading air locker brand worldwide.  When disengaged, the locker acts like a normal open differential, but when air pressure is applied from a separate compressor, a locking collar slides forward and locks the gears together.

Two significant benefits with air lockers are that they engage in less than a second and can be activated at any vehicle speed – providing the axle shafts are spinning at equal rates.


Harrop E-Lockers use an electromagnet to lock the differential by pulling two roller cams apart, and use bearings to maintain the separation. This drives heavy pins down into the side gear of the differential, locking the unit.

E-lockers do not require an air compressor to be installed. Whilst this simplifies installation, e-lockers rely on roller cams for engagement, which means that some rotation will need to occur in order for the locking mechanism to engage. Improper engagement can cause damage, so some care is needed.

E-Lockers are fitted as OE standard equipment by Toyota and other manufacturers.

“Front or Rear?  Or both?”

Whilst it is optimal to install both front and rear lockers, it is also costly.  If the purpose for installation is to maintain traction while towing or for light off road use only, a rear locker may suffice.  However, for pay-and-play off-roading, a front locker can be more helpful for a 4WD vehicle.

“Air Locker or E-Locker?”

Either type of locker will offer a significant benefit in light off-road use such as camping or green laning, and will effectively lock the diff on demand, increasing traction.  For remote area travel and overland use, E-Lockers excel. For competition or “pay and play” use, air lockers are our preferred choice.

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4×4 Works are one of the UK’s best known premium 4WD upgrade specialists.  We import and sell the best products from around the world.

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