What are automatic differential locks?

Automatic diff locks will push you further down the track without any driver input.

What are automatic differential locks off roader

When compared to manually-operated differential locks (which we looked at earlier), auto lockers require no driver input, but they also help the inexperienced off-roader to get further down a difficult track than his or her ability might otherwise allow.

This article was originally published in 4x4 Australia’s July 2012 issue

Conversely, they may take such a driver further into trouble as there is no need to read the terrain ahead, as is the case with a manual locker that needs to be switched on and off. The auto locker does all that for you on- and off-road.

These lockers are at work all day every day on all road surfaces. Driving up a slippery boat ramp, skating around on slimy, muddy tracks as well as tackling your favourite rocks and ruts, the auto locker will be helping you look the hero at all times. Besides having a much lower price tag than manual diff-locks, the big plus with auto lockers is the fact that they are more suitable for front diffs as they offer easier steering compared to the (almost) non-existent steering you have with an engaged manual locker.

Now, this is where many people become a little confused with the operation of (most) auto lockers. They are, in fact, in the locked position when you are driving straight ahead and unlocked when you turn a corner when the outer wheel is turning faster than the inner wheel.

This wheel overrun is then re-locked when both wheels are rotating at the same speed again. So now you have a locked diff for those hairy situations plus a diff that’s effectively open for on-road use and ease of steering, all rolled into one.

There are however a couple of negatives including some clicking and/or clunking as the locker’s teeth disengage and engage. Also, with some 4X4s, or when tackling tight turns and roundabouts, you may feel a slight resistance to the steering input and your turning circle may be larger as the locker cuts in and out.

Your driving style may also affect the workings of an auto locker as too much on and off with the throttle while cornering tends to upset some units. You’re also likely to get a little higher tyre wear with this type of on-road use.

In off-road situations, though, while powering through a difficult obstacle, the diff will remain locked regardless of whether you’re turning, during wheel slip or even with wheels lifting off the ground, and that’s exactly what you want. It’s the driving torque from the engine, acting on the diff’s internals, that keeps the locker in the locked position.

So, without any input from the driver and no predisposition of how difficult the terrain, your auto-locker-packed 4X4 will outperform stock-standard vehicles hands down. Onlookers will bow down on the tracks in disbelief at your driving skills – just don’t tell them your ride is modified and no one will be any the wiser.

Oh, and your ride need not be a highly modified semi-competition vehicle to benefit from installing auto lockers. The average family 4X4 will reap the rewards equally, as will dad with his kids strapped into the back seats. Conquering those harder tracks is always news-worthy stuff for kids when they get back to school. 


The Powertrax Lock-Right automatic locker is manufactured in the USA by Richmond Gears and incorporates couplers with ramped teeth that are maintained in the locked position when the vehicle is driven straight ahead. The higher the drive input, the more firmly the opposing teeth are locked into position.

The unlocking happens when the faster (outside) wheel overruns the slower (inside) wheel via the ramping and cross shaft. The Lock-Right replaces the planetary gears, but retains the OE carrier, crown wheel and the ring and pinion gears.

For more information see www.Richmondgear.com.


Probably one of the best known auto lockers in the world, the Detroit was one of the first of its kind to offer a differential effect and total automatic locking. It provides full drive to wheels on both sides of an axle via a series of spring-loaded clutches with interlocking teeth. The automatic disengaging of these teeth happens during wheel overrun (turning corners). The automatic re-engaging happens when the axle speeds equalise. This, in effect, provides (on-road) differential effect while offering off-road locking qualities.

Over the years, the Detroit has evolved to the current Soft Locker version where the interlocking teeth have been ramped on the leading and trailing faces to help avoid the severe clunking often associated with auto lockers during operation. Belonging to the same Detroit family is the No Spin, but it comes without its own hemisphere casing and is aimed more towards industrial and truck use. The Detroit, however, is set in its own case and drops into your diff housing.

Yet another offering from Detroit is the Truetrac. Not really a true diff lock, it uses a helically-geared limited-slip diff centre, as opposed to an OE clutch-pack-style limited-slip diff centre. The Truetrac will certainly get you further down the track than an open diff, but it’ll never perform as well as an proper auto locker for 4X4 use. There’s a comprehensive range of Detroit lockers available for front and rear fitting for most 4X4s.

For more information visit www.harrop.com.au, call 1300-HARROP, or check out Harroptv on YouTube.


Made in Australia, the Lokka has very few moving parts (a pair of cam and axle gears, plus springs and pins) and utilises a cam mechanism to keep itself locked. The heat-treated alloy Lokka replaces the planetary gears, but keeps the OE carrier, crown wheel, ring and pinion gears.

The locking action happens when the pinion cross shaft engages its mating surfaces. The more power that is fed into the diff via more throttle, the harder the surfaces clamp together. The unlocking happens via the ramping effect of the low-profile teeth when one wheel tries to overrun the opposite side wheel. The low-tension springs allow this unlocking action to take place even on surfaces with poor traction.

For more info see www.4wdsystems.com.au, call 08 8369 0033 or drop into the head office at 599 North East Road, Gillies Plains in South Australia.


Manufactured by USA Standard Gear in the States, the Spartan Locker is a mechanical-locking unit that drops into the OE carrier and replaces the spider gears. The Spartan utilises high-nickel-content chrome-moly parts and maintains the standard case.

Low-profile ramped mating teeth, combined with springs and pins allow easy unlocking and locking action.

For more information visit www.wooders.com.au or call Wooders Garage on 02 9477 4312 or drop into unit 2/4 Leighton Place, Hornsby, NSW.


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Mark Allen

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