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Buyers Guide to Aftermarket Diff Lockers

A differential is part of the 4WD driveline, allowing the wheels to spin at different speeds when cornering. This also means that when you’re out four-wheeling and a wheel gets some airtime, the axle sends all the power to that wheel instead of the one that is on the ground. Not very helpful when tackling a gnarly track because it means you lose traction and momentum. 

By adding a diff locker, an equal amount of power is sent to both wheels in a 50/50 split, making this one modification to your 4WD that will help it go a lot further. These days, some modern 4WDs come with rear diff lockers as standard, but this still leaves many people wondering what type of aftermarket diff locker suits their 4WD the best.  

Air locker 

ARB was the first aftermarket company to develop an air locker for 4WDs, with their ARB Air Locker, followed by TJM with their Pro Locker. An air locker engages when air is forced into the diff via an air compressor which must run until you want the locker to disengage. 

ARB Air Locker


  • Manually selectable
  • Quieter operation
  • Provides instant traction
  • Reduces wear on other vehicle components


  • Expensive
  • Not an easy DIY install
  • Susceptible to oil/air leaks

Electric locker

Electric diff lockers, such as the Harrop Eaton E-Locker, engage and disengage by providing 12V power to the unit. In most cases, they use an electromagnet that is powered on and off as needed, making the differential lock and unlock.

Harrop E-Locker


  • Easier to install
  • No need for an air compressor 
  • Up to you as to when you want to engage or disengage


  • Needs to be installed by a professional
  • Can be issues when switching from reverse gear to forward gears
  • 4WD must be stationary to engage the diff locker

Automatic Locker

An automatic diff locker is the simplest option as it is 100% mechanical and always locked until enough cornering force is applied to unlock the differential. What this means is that the auto locker is in the locked position when the 4WD is driving straight and unlocked when turning a corner and the outer wheel is turning faster than the inner wheel. When the wheels return to rotating at the same speed, the auto locker reengages. Automatic diff lockers available in Australia include the Lokka auto locker, Detroit locker and Spartan locker.

4WD Systems Lokka


  • Cheapest diff locker option
  • Easy to install
  • 100% mechanical 


  • The driver has no control over when the locker engages and disengages
  • Can affect the 4WDs drive characteristics
  • Noiser than other diff lockers

Front, Rear or Twin Locked

Front Locker


  • Better control to get the front wheels up an obstacle 
  • Provides better traction for 4WDs with Limited Slip Diffs


  • Difficult to steer when engaged
  • Struggles if the rear wheels lose momentum

Rear Locker


  • Provides better traction
  • Keeps the wheel speed under control
  • Keeps climbs and descents more controlled


  • Inexperience in use can cause issues with control
  • Can cause larger wheel lifts

Twin locker


  • Provides the ultimate traction control
  • Improves the capability of the 4WD
  • Gets you further


  • Expensive to buy and install
  • Can lead to a false sense of security about the ability of the 4WD and the driver

Next steps

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  • John Crocombe: May 17, 2023

    With regard to “Automatic” Lockers, I believe that they are under-rated. They are hands free and take all of the guesswork out of when to lock and unlock them in offroad situations.

    When driving, as far as I am aware, the driver can still get them to unlock in turns, by backing off the throttle, just before starting to turn. Once the vehicle is turning, an automatic locking diff will only drive the “slowest” wheel, until both wheels are rotating at the same speed again, then relock.

    Automatic diff lockers may well be noisier than air/electric lockers, but they are still not that loud to worry about and seem to be more reliable than other types.

  • Jeff: May 17, 2023

    Most 4×4 are only 2 wheel drive, until you add two diff locks

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