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There is some confusion out there among the four-wheel drive community. It seems some feel that having diff locks fitted to a vehicle is overkill, yet having a big lift kit and a catalogue worth of weighty accessories is money better spent. If you genuinely feel that way, ask yourself: why do most new four-wheel drives come with (or have the option of) at least one diff lock from the factory? Yet how many new vehicle manufacturers offer a lift kit as part of their factory optional accessories? Not many!

It is quite simple when you break it all down – traction is king off-road. Setting up a four-wheel drive in my opinion takes a three-pronged approach. You need clearance, which comes from fitting slightly taller suspension. You need better tyres for puncture resistance and off-road grip (a taller size will provide more diff and ground clearance too), and (at least) one cross-axle differential lock to provide you with a minimum of 3WD when required. In fact, it is amazing where you can take a stock four-wheel drive these days thanks to having just one locker.



Enhanced off-road traction (well… duh)

Stronger than factory components (like the differential carrier)

The ability to continue driving in an emergency situation with a broken axle or CV joint (with the offending part removed)

Unmatched off-road control with the ability to drive obstacles slower

Minimised track damage thanks to reduced wheel spin

Less chance of breaking driveline components

Lifting a wheel no longer translates to “get the winch out”

Increase in vehicle resale value

Pneumatic lockers require compressors that in some cases will inflate tyres too

Air lockers make that cool ‘PSSSSHHTTT’ noise… You know what I mean!



Some four-wheel drives are offered with the option of installing factory diff locks. Think Jeep Wrangler Rubicon, Mitsubishi Pajero, Toyota LandCruiser… there are plenty. In fact, a rear diff lock was only a $500 option on Mitsubishi Tritons… you would be mad not to tick that box! It must be mentioned though, that factory lockers if not standard inclusion can cost more then aftermarket units, so always do your sums before signing on the dotted line. Also, tracking down replacement components for factory diff locks could prove tricky in remote settings, whereas aftermarket suppliers will have the parts on the shelf ready to send out (well, in theory).



The cheapest form of traction enhancement is known as a lunchbox, drop in or simply an auto locker. These units are designed to sit inside the factory differential carrier, replacing the stock spider gears and in some cases the side gears and cross-shafts. There are no compressors or external lines required, operation is automatic and completely mechanical.

These lockers are actually un-lockers, as in a straight line with power applied they offer drive to both wheels, but will un-lock when different torque loads are detected, such as with no power being dialled in while going around a corner. And this is how you need to use them… power on – locker is engaged, lift off the accelerator for a corner and the device will un-lock.

They can be quite agricultural in operation though, with many users reporting clunking and banging noises similar to a pistol shot when driving on high traction surfaces. Keep in mind, fitting any auto locking differential to the front differential of a full-time 4X4 will make it drive worse than a poorly-maintained steam roller, but they can be installed front or rear in a part time four-wheel drive. Many choose to install them in the front differential, as with the hubs unlocked (in the ‘free’ position) the locker has no affect whatsoever. Put the vehicle into 4WD with the hubs locked though, and you will experience a want for the vehicle to keep travelling straight, no matter how you’ve got the steering wheel turned.

For sheer simplicity and cost effectiveness, lunchbox lockers are a great entry-level option for those who are prepared to alter driving styles and live with their quirks.

Examples: 4WD Systems Lokka, Powertrax Lock-Right, Yukon Spartan, Detroit EZ Locker, Aussie Locker

Perfect for: Those on a budget, or in the front differential of a part-time four-wheel drive for weekend warrior types



The holy grail of auto lockers are known as full carrier replacements. They do just that; replace the stock diff carrier and internal gears with the only components retained being the factory crown-wheel and pinion (this is the perfect time for a diff-ratio change if you have larger-than-stock tyres).

Locker activation is more civilised compared to lunchbox lockers, as by design the engagement is less vicious. This is due to the gradual teeth engagement profile, and ratchet style locking mechanism. As with lunchbox lockers, full carrier replacements are always locked, yet will unlock while cornering with less throttle applied. More specifically, they will not allow a wheel to spin slower than the input from the driveshaft. They will however allow one wheel to spin faster than the driveshaft, which is exactly what the outside tyre wants to do while cornering.

Full carrier replacements are constructed from stronger than stock materials in most cases, including forged steel or high-grade nickel-chromium molybdenum. There are no buttons to press or activation lines to run which is part of the appeal. These lockers require no input from the driver while off-road, so the chance of getting bogged is reduced. On-road handling is compromised slightly, but as with lunchbox lockers, a change in driving style and an awareness of the locker’s presence is all that is required to combat this.


Examples: Eaton Detroit Locker,
Yukon Grizzly

Perfect for: Those who want added levels of traction without requiring driver input



Air or vacuum operated selectable lockers (pneumatic lockers) have long been favoured in this country by tourers and hardcore four-wheel drivers alike. The reason for this is the fact they can be locked or unlocked with the push of a button; meaning uncompromised handling on-road and traction when you need it off-road.

There are a few different varieties of air operated selectable lockers, however they all work in similar ways. Compressed air is fed into the differential housing from a permanently fitted air-compressor through a pneumatic line. Air pressure is regulated from the compressor to roughly 95-115psi, and this compressed air enters the differential through a specially designed seal housing. Once activated, a piston slides the clutch gear into the locked position. This locks the differential side gears to the housing, thereby locking the differential. Vacuum lockers used by the Land Rover crowd work a bit differently, as they are activated by negative pressure created by the vehicle’s vacuum pump, but it’s essentially the same principle.

Air operated selectable lockers can be fitted to the front or rear diff of both part-time and full-time four-wheel drives. There are negative points though. If a compressor or pneumatic line is damaged, the locker will not activate. Also, as they are manually selectable diff locks, if you forget to switch them on in time it could be too late.


Examples: ARB Air Locker, TJM
Pro-locker, Maxidrive Locker, Ashcroft Air Locker, Yukon Zip Locker

Perfect for: Those who want the best of both worlds. An open differential for on-road use, 100 per cent locked when required off-road.



The latest kids on the locker market are electronic lockers such as the ELocker made in partnership by Harrop and Eaton. Harrop manufacture the diff locks in Melbourne using forged gears sourced from Eaton in America. The benefit of electronic lockers is the fact that no air compressor or pneumatic lines are required. They are still fully selectable as per pneumatic diff locks with simple push button operation; yet need only two wires to be run to the differential. If these wires are damaged off-road, they can be repaired far easier than repairing a pneumatic line.

Operation is damn near silent, and is also instantaneous. The mechanism utilises an electromagnetic locking system with four pinions. This allows the diff to perform as an open differential. When the locker is activated, the electromagnet engages pins that effectively lock the differential’s side gear to the carrier. No fancy pixie dust or black magic, just good old Aussie engineering.

The ELocker comes with everything required for the install too, such as a wiring harness with convoluted tubing, in-dash switches and even a few cable ties to make installation far neater.


Examples: Harrop Eaton ELocker

Perfect for: Those who want a selectable locker, but don’t like the idea of running compressed air or pneumatic lines into their diffs



Kam Lockers: These just look cool! Kam manufacture beefy half-shafts and diff ratios, as well as limited slip diffs and full diff locks. Their lockers are electronically controlled, and protected with their own sturdy diff pan cover.

OX Cable Operated Lockers: Cable operated diff locks? Yep! And they work bloody well too. There is something satisfying about clunking the shift lever into position, even though they can be set up to run pneumatically, too.

Kaiser Lockers: Brazil based Kaiser manufacture auto lockers for a range of outside-the-square vehicles such as the Daihatsu Feroza and Kia Sportage. If you own something other than a Patrol or LandCruiser and can’t find a locker for your truck, it’s time to start learning how to speak Portuguese!

Air Locker (rip offs): You might have seen these on 4X4 forums, or online auction sites. Hey, they might look the same as ‘the branded ones’, but how can you be sure they aren’t made from recycled coke cans and melted down Holden Barinas?

Lincoln Locker: CIG Locker, Lincoln Locker… also known as a welded diff. This involves welding the stock spider gears together, locking the diff solid. Don’t make the mistake of welding the crown wheel to the pinion; actually… just don’t weld your diff at all unless the vehicle is strictly off-road only. It’s dangerous and highly illegal!

Mini-Spool: Spools replace the factory spider gears with a solid piece of metal (usually heat treated steel), locking the axles together. These are permanently locked, and not legal for road use. For off-road use only though they are far neater solution than welded diffs.


Words by Evan Spence


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