4WD DIFF LOCK COMPARISON – FRONT VS REAR VS TWIN LOCKED + AIR VS AUTO VS E-LOCKER
If there is one question we get asked most at 4WD 24/7, it is usually “Should I fit a diff locker?” or “Should I get a front or rear locker?”. Jocko tests this question with his Hilux to see which differential locker works best, while explaining how a differential works, and how lockers work too.
WHAT IS A DIFFERENTIAL?
A differential is a component of your 4WDs driveline, which essentially allows your tyres to spin at different speeds as your vehicle turns corners. As you drive in a straight line, your tyres move at the same speed as each other, but when you turn a corner, your outside wheel has to spin faster than your inside wheel because it has to cover more distance in the same amount of time. If your axels are connected together, when turning, the inside wheel would bind up and not allow you to turn properly.
The gears within your differentials allow each axel – therefore each wheel – to spin independently. This system works perfect for on road driving but faces problems when 4WDing. When offroad, once you get a tyre in the air, one side is holding pressure so it can’t spin while all of the drive will go to the tyre in the air, which is useless.
The best way to fix all the drive going to one wheel and not the other is to install a locking differential. There are plenty of brands and types on the market, but essentially you either have selectable lockers or automatic lockers.
Selectable Diff Locker
The way a selectable differential lock works is by physically sliding a locking ring onto one of the side gears inside the casing. This essentially locks all the gears together, providing 50/50 drive to each side, which means even if you are 4WDing and a tyre goes in the air, the tyre on the ground will still have drive and you can continue moving forward. A vehicle without a locker will only power the wheel with the least resistance – the tyre in the air.
All selectable lockers follow the same principle, the only differences are the designs of the mechanism and how the locking ring gets activated. Electronic lockers use an electromagnet to activate, and air lockers use compressed air.
REAL WORLD DIFF LOCKER TEST
Jocko has gone out to test out all kinds of diff locks and to answer the questions about what types you should get, whether to choose a front or rear locker first, and which ones make the biggest difference.
Intense Steep, Slippery Rock Crawl Climb
TEST 2: Slippery Rock Climb, Less Intense
For these tests, Jock used selectable air lockers – front and rear – in his Hilux. We drove a steady 1500rpm up the test track, with tyres at 15psi, driving unlocked until we stop, then repeat the test with only the front diff lock engaged, then only the rear, and then finally with both diff locks on.
No Lockers Engaged
TEST 1: The vehicle was only able to start the rock step climb, coming to a point where both the front and the rear of the 4WD were trying to climb to separate steps. Wheels were lifted and therefore, traction and drive was lost, and the unlocked vehicle couldn’t climb the step without strenuous track building or winching.
TEST 2: Same results as above – struggled for traction and drive and couldn’t pass the track without track building or winching.
Rear Locked Only
TEST 1: Similar results came in this test as the unlocked staying at around 1500rpm, but with a bit more momentum the vehicle should be able to make it further – given you don’t drive to hard and potential damage your 4WD. Again though, traction was lost in the front of the vehicle and the Hilux was unable to progress through the challenge.
TEST 2: With lack of grip and power due to the unlocked front axle, the 4WD got stuck early on the track when driven steadily around 1500rpm. Again, more momentum without pushing the vehicle too hard would likely help.
Front Locker Only
TEST 1: With the rear diff lock disengaged and the front locker turned on, the 4WD was able to have continuous drive from both the front wheels and could make it pass the rock step with a bit more momentum, just not around the 1500rpm range. Traction and drive were now lacking in the rear of the vehicle, still making it difficult to climb.
TEST 2: With only the front diff lock engaged, it made a noticeable difference as the nose of the vehicle was able to climb obstacles and pull the rest of the 4WD without the use of a rear locker. This was able to finish the less intense slippery rock climb on its own power, not pushing over 1500rpm.
Fully Locked – Both Front and Rear
TEST 1: With slightly more momentum, the vehicle was able to conquer the huge and slippery rock steps and finish the track on its own power.
TEST 2: When twin locked, the 4WD was able to get the most traction possible in both the front and rear of the vehicle and was easily able to steadily drive the whole track. The more technical and difficult lines are easier to drive with slow control provided by the diff locks.
PROS AND CONS
- More control to get the front tyres up an obstacle
- The vehicle won’t pivot around as much, keeping the front of the 4WD on track
- Can make up for lack of wheel travel in IFS 4WDs
- If you have a tight rear Limited Slip Diff, capability will significantly improve
- Harder to steer in tight & technical situations when engaged
- Can struggle if the rear falls into a hole and there isn’t enough momentum
- Pushes the vehicle forward
- Allows you still use full range of steering while driving
- While descending, it can help to keep your 4WD controlled
- Comes in most new vehicles these days
- A loaded and heavy vehicle will pivot around the rear axle
- Can make wheel lifts bigger as the vehicle torques over while driving
- Ultimate control and driving ability
- Increases capability massively
- Expensive to set up
- Can put you and your 4WD in more extreme and sometimes risky situations
It is no secret that being twin locked definitely give you the most amount of off-road control, plus it allows you to pick more technical lines and tracks, making your driving and 4WDing skills develop to be a lot better as time goes on.
Having a rear locker only definitely gives you a lot of control when 4WDing, and it doesn’t affect your steering. If you have bought a new 4WD, chances are you already have one installed.
Personally, we prefer a front diff lock first from the testing we conducted. Jocko noticed that with just a front locker, the vehicle kept much more on track and kept the vehicle straight. It was also able to climb obstacles easier as the nose of the vehicle was able to continue to crawl in situations where traction would normally get lost. As the locker was selectable, if you did need to readjust, you could simply reverse, turn the locker off, readjust, then engage the diff lock again.
Another reason why Jocko prefers front diff locks is because when he first purchased his Hilux, it was an IFS (Independent Front Suspension) Vehicle, and he installed a second-hand front locker, which took its 4WDing capabilities to the next level. Because IFS vehicles don’t have a large wheel travel range and often lifts wheels, installing a front locker allowed the front to always have drive during these situations.
WHAT LOCKER TYPE SHOULD YOU CHOOSE?
There are essentially 3 main types of lockers on the market today: air actuated lockers, electronic actuated lockers, and mechanical/auto locking diffs. There are also a very uncommon cable actuated lockers which we won’t focus on here.
When it comes to purchasing a diff lock for your 4WD, we consider there to be 2 main factors that will affect the locker that you choose: that being your budget and your driving style.
Selectable lockers like Air and Electronic diff locks are the most expensive to install, but they give you the most control because you can decide when to turn them on or off whenever you need extra traction.
As they are controlled by a switch, when they are not engaged, the differential will act as normal. So, when driving on the road, it will become an open diff and you would not notice that you have a diff lock. Obviously, the disadvantage comes with the cost, with an air locker normally pricing around $1,000 or more depending on the model of your 4WD.
For air lockers you also need an air source installed, so factor that in your budget if you do not have an on-board air compressor. These compressors for your air lockers can be installed under your bonnet like Jocko, or even in your canopy.
Another disadvantage of the air locker is that, if not set up properly, you can get air leaks in the system which can result in a lot of pain when you’re out in the bush and your lockers aren’t working.
Aftermarket electronic diff locks are typically more expensive for the locker itself, but the advantage comes with a straightforward installation. You need to install a wiring loom, a switch, and run power down to your diff when the locker is installed inside. As you don’t need to install a compressor and airline, the pricing turns out to be similar to an air locker.
If you are on a bit more of a budget, bang for buck, it is hard to go past an Auto Diff Locker, like the ones installed in Jocko’s Pony Hilux. These work a bit differently yet are a simple and effective way to gain extra traction.
Auto diff locks are essentially always in a locked state and will unlock when there is differential action. Put simply, when one tyre is spinning faster than the speed of the differential - like when turning a corner – the auto locker will disengage.
These are a great option, particularly if your vehicle does more 4WDing than typical on-road driving. One thing that we have found with Auto lockers when Jocko entered the Pony Hilux into a 4WD competition, was when driving slow and technical tracks it can be difficult to turn. A way around that was to rock the vehicle back and forth, or to unlock one hub to release the locker.
Another disadvantage is when they unlock as you drive around corners, they tend to be clunky and loud on the road, and you do notice them in.
The main advantages of an Auto diff lock are the fact that you do not have to run any wires to your differential, and no need for a permanently installed compressor with airlines. They are typically half the price of a selectable locker.
Making Your Choice
It comes down to your budget and being honest with your driving style. Jocko has used Auto lockers in the Pony Hilux, a mostly off-road only vehicle, and air lockers for 5 years in his SASed Hilux that have never let him down.
What matters above all else is how your diff lock system is installed. You need to ensure that it is installed by a professional who knows their way around differentials and lockers – because if they are set up wrong, they will only cause issues and dramas.
THE 4WD 24/7 EXPERTS OPINIONS
Here are some of the experiences, preferences, and opinions from the rest of the team and faces at 4WD 24/7.
If you own a vehicle like his big GU Nissan Patrol, that has a solid LSD in the rear, you can install a front locker and get the best of both worlds. Personally, for Graham though, he prefers the feel of the way a 4WD drives when a rear diff lock is installed opposed to the front. “You push a wheelbarrow; you don’t pull a wheelbarrow” so a rear diff lock – like in the GU and his D-Max - is Graham’s choice.
In terms of types of locker, take auto lockers out of the equation; they do have their place, but Graham has never been a fan. His choice would be air lockers, as he has never had an issue in 15 years, and the compressor kit also allows you to be able to pump up your tyres – two birds one stone!
For Shauno personally, if he had to choose only one diff lock to be installed, it would be a rear locker. As Toyota’s tend to have a weak LSD, a rear diff lock makes your 4WD a heck of a lot more capable, and says a rear locker is the best bang for buck 4WD modification.
Shauno has tried and tested every type of differential locker under the sun, but the strongest from his experience would be air lockers. He previously broke 5 E-lockers in a row before he swapped back to air and has not had any major problems since. Air diff locks tend to be more bush proof and if it is installed correctly it won’t leak.
Rocket Rod – Wholesale Automatic Transmissions
Without a doubt, his choice is a rear diff lock for his 79 Series, as it often lifts wheels when tackling hard obstacles, knowing he can count on his rear wheels when they are the only ones grounded.
From Rocket’s experience of both air and E-lockers, he prefers E-lockers as they tend to come factory with some vehicles and he has never broken one.
Pete – Ultimate 9
In an ideal world with a budget that allows, it is great to have both front and rear. But when forced to choose just one, a rear diff lock is very handy to minimise the roll of the vehicle while descending a steep hill and is also handy through deep ruts and bog holes when you need to push the car through. The front locker is more for the applications of rock steps and hill climbs where you need the nose of your car over that obstacle.
Pete loves the flexibility of instant on and off that comes with using air lockers and has used air diff locks for 20 years. They have always been trustworthy and reliable and are a favourite accessory for his trusty GU.
Rueben – DMW
If you can only choose one locker for your 4WD, you should put it in the rear because when climbing hills, it will transfer more weight, traction and drive to the rear, and the rear diff lock will push you up where you want to go.
Rueben choses an air locker as he already has air compressors on board all of his 4WDs to pump up his tyres, so he utilises the compressor for his diff locks too.
Tim – Mits Alloy
With no lockers at all, choose a rear diff lock first because you tend to have a lot of weight in the back, and you are better off pushing rather than pulling up a hill.
Air lockers tend to be much stronger, but come with the downside of installing a compressor, installing the electrical circuits for it, as well as maintaining the compressor and the airlines. E-lockers are simpler with just a switch running power but aren’t as strong. Depending on your 4WDing demands and how hard of tracks you drive should decide what strength you need.
THE DIFF LOCKER FOR YOU
The best way to understand in the real world for what you should choose is to try and borrow a 4WD with lockers if possible and test it for yourself, ideally in a vehicle similar to yours. If you do not have access to a test drive with lockers and different types, take the above advice from our team to decide which application suits your 4WDs demands the best, as well as properly budget for your locker choice.
Just remember, whatever differential locker you decide to install in your 4WD, ensure it is installed and set up perfectly to give you a long trouble-free life