The only way you’ll be able to get the most out of your 4X4 vehicle is if you understand the fundamentals and that involves getting to grips with the various components that make your 4X4 behave like an off-road vehicle. The locking differential is as good a place as any to start.

Understanding differentials

The differential has three jobs – direct engine power to the wheels, slow the rotation speed of the transmission before it hits the wheels and transmit power to the wheels that allow them to rotate at different speeds. 

A differential will always, by default, direct power to the wheel that’s easiest to rotate. This allows the vehicle to turn more efficiently and is perfectly fine in conventional circumstances. But we’re not interested in conventional circumstances.

What is a diff locker?

Often shortened to “Diff-Lock” or “Diff-Locker,” locking differentials are modifications to the standard differential that exist to restrict the wheels on an axle to the same rotational speed, regardless of how much traction is available to each wheel. 

You see, whilst a locked differential makes sense for a vehicle that only travels on hard surfaces like roads, when you start navigating uneven off-road surfaces, it represents a few problems. 

Say, for example, you get stuck in a situation where your rear wheel is left spinning in the air after a particularly nasty bump. 

An open differential will send all of its power to the wheel that’s stuck in the air and you’ll be unable to move as a result. If that differential was locked, however, it would spin both wheels and allow you to escape.

On the other hand, in low-traction scenarios, with one wheel spinning faster than the other it can cause the wheel to ‘dig in’ and make the situation worse. 

This is why they are so useful in 4WD and off-road vehicles – they allow you to lock the differential with just the flick of a switch and increase traction to help you out of sticky situations. 

But what are the different types of diff-lock on the market and should you install them on the front axle, the rear axle – or both?

Front or rear? 

Installing locking differentials on both is obviously the best option if you can afford it. However, if you can only afford one then it depends on how you’ll be using your 4X4.

If, for example, you will be using it as a tow truck in light road use then a rear locker would be the best option. When doing general off-roading, however, a front locker would generally be more helpful.

E-lockers or Air lockers? 

As the names suggest, E-lockers are controlled electronically while air lockers are controlled by air pressure. 

The benefit of air lockers, like those made by ARB (the leader diff lock brand in the world), is 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. 

E-lockers, such as those produced by Harrop, don’t require an air compressor to be installed, which greatly simplifies installation. 

As for which choice will benefit you and your vehicle more? That, once again, depends on what you’ll be using it for. For light off-road use, both will be able to lock the differential on command to increase traction when required. 

However, for overland use, E-Lockers are generally more reliable. Air lockers are perceived by many, meanwhile, to offer a competitive advantage for professionals.

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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.