www.4×4tec.co.za

Firstly, this article is only about Axle diff-locks where the two drive shafts/wheels are locked together on the same axle, to evenly split the power between the 2 wheels.

Many permanent 4wd vehicles also have a differential in the transferbox, which can be locked and this mechanism is called Centre Diff Lock, but this article is not about Centre Diff Locks, it’s about Axle Diff Locks, so please make sure you know which type your vehicle has.

A Diff-Lock does just what it’s name says, it locks the differential. Any mechanism that does not completely lock the 2 wheels together as some point during it’s operation, is NOT a diff-lock.

A quick overview of other traction aiding devices, other than diff-locks.

Limited Slip Diff (LSD) – A mechanism which transfers torque from one wheel to other by means of friction in a clutch pack or a geared system. One wheel has to spin faster than the other to initiate torque transfer.

Viscous coupling – A mechanism that uses the increased viscosity of a liquid during excessive wheel spin to transfer torque from one wheel to the other. Works in a similar way to a LSD, where one wheel has to spin faster than the other to initiate torque transfer.

Traction control – A system that electronically monitors wheel speed and applies the brakes to the faster moving wheel to transfer torque to the other wheel. There are different names for this type of system by they all work in a similar way by using the ABS sensors to monitor wheel speed and then apply the brakes as needed. Again one wheel has to spin faster than the other to initiate torque transfer.

Back to diff-locks. There are many makes of lockers(slang word for diff-lock), but here are a few main types:

Selectable Lockers:

This type of locker can be activated with a switch inside the vehicle. Activation can be achieved in various ways, with a mechanism driven by an electric motor(popular with OEM’s), with air, with hydraulics, with a cable, with vacuum, etc. A selectable locker usually consist of a static and a sliding part which engage onto each other with teeth. Both parts turn with the differential, the static piece is fixed to the diff carrier, while the other slides to either lock one of the gears or a shaft to the diff carrier. When the diff-lock is activated the sliding part is advanced by one of the above mentioned mechanisms. The teeth will then engage onto each other to lock the differential. The teeth will usually not line up immediate and some differential movement is required to make them line up to engage. Switching the diff-lock on while wheel spinning will cause these teeth to meet up at high speed en they could possibly break. The speed at which the diff-lock engages is influenced by the speed of the activation mechanism and the line-up of the teeth.

Here’s a video that shows how Eaton’s selectable E-locker works:

Auto Lockers:

This type of locker cannot be switched on at will. It is basically permanently locked and when you go around a corner on a sealed surface under neutral throttle, it disengages to allow the wheels to turn at different speeds. Without going into too much detail, it works basically with a cam system that pushes toothed discs against each other. Being a cam system, it means the more torque you put into the axle, the harder the diff locks. The same goes for when driving under compression, torque goes from the axle into the prop shaft, putting pressure on the cam system and locking the diff. That’s why neutral throttle around a corner is so important. These lockers also have teeth but shallower that those of selectable lockers and with angles on the side of the teeth to allow slippage between the teeth when not under load.

This type of locker could induce understeer when you don’t want it and that’s even worse on a short wheel base vehicle. Think carefully before installing an auto locker because it can cause problems in certain situations. They are usually a cheaper or more reliable solution, but a selectable locker will usually be the better solution.

This is what a typical auto locker looks like. This one is the EZ-locker I installed in my Land Cruiser a few years ago.

Auto locker with full engage/disengage function:

In the last few years a new type of auto locker has been developed which is very road use friendly. It uses a mechanism that allows the diff to be completely unlocked during normal operation. Then when one wheel looses traction a geared system will spin a small shaft at high speed, that swings out a weight that locks the diff. See the link and videos below for a proper explanation. This is definately the ultimate in auto lockers and the type of reliable machanical system manufacturers can install on daily driven vehicles. The engagement however is a bit violent for my liking.

http://tariqhafez.blogspot.com/2011/01/how-eaton-g80-locker-works_19.html

A video about the Eaton G80:

http://www.youtube.com/watch?v=tTGZOJQQBeE

Diff-lock/LSD combo’s:

Recently manufacturers have been offering Limited Slip Diffs with a selectable locking option. This gives you the benefits of an LSD on loose sufaces like snow, sand or mud as well as the ability to lock the diff for more serious offroading where the wheels will be lifted off the ground.

Lincoln Locker:

This is an American term for a welded diff, referring to the Lincoln make of welder. This is basically an extreme low budget way of locking the differential by welding the gears to the diff carrier or the gears to each other. This is for extreme offroad toys and not at all recommended for on road use. I have done this before on a Series 2A Land Rover and also on a Suzuki SJ410. The SJ410 with it’s light weight was still pretty usable on road and I used it in town eventhough the diff was completely locked….but it is definitely not recommended.

Here’s some pictures of the diff I welded up.

Spools:

Spools are solid replacements for a diff carrier and gears. It’s also permanently locked like the above mentioned welded locker, but you don’t destroy your existing good differential. This means you can change back to the standard diffrential at a later stage. This is also only for extreme offroading and not for on-road use.

A typical Spool:

My vehicle has no diff locks, where do I start, what do I buy?

Firstly start off by looking what you use your vehicle for. If you use it as your daily driver and mostly on tar, a selectable locker is your only option. If it is your weekend or touring vehicle, you can consider an auto locker. An auto locker is not very easy drive with on a daily basis and as mentioned can be a problem off-road in certain situations as well.

If you have to go for a selectable locker your options are very limited in South Africa. You can basically choose between a Gearmax diffloc and an ARB air locker. There are many other makes but they don’t have any support or fitment centres in SA. The Gearmax locker is locally developed and although there have been many complaints about them, they do the job well and it’s the cheapest selectable diff lock you can buy. The only problem with the Gearmax is the very limited range and they mostly focus on OEM’s. They did do an aftermarket diff lock for the Land Rover Salisbury diff, but that product has been discontinued. My sources in the industry say they have developed a new more reliable mechanism, but it sounds like they will only supply OEM’s. For a selectable locker this leaves you with ARB. The ARB replaces the whole diff carrier and is actually stronger than the factory differential. They are however very expensive, around R14 000. Even at this price, if you have no diff locks yet, it’s worth it. I fitted a rear ARB locker to a ‘95 Discovery and with stock suspension and small road tyres, there was almost nowhere it couldn’t go.

For auto lockers there are many options. The strongest and the most expensive is the incredibly strong Detroit Locker. Like the ARB it replaces the entire diff carrier. It is probably the strongest and most reliable difflock on earth! Besides the Detroit, there are a few companies that make what is commonly known as a “lunchbox locker”. These lockers are installed into the existing diff carrier and replaces the differential gears. Some of them aren’t very strong and I’ve broken 2 lunchbox lockers of different makes on 2 different vehicles.

Where do I fit a locker, rear, front or both?

If you have no locker and you want to greatly improve your offroad ability, without the need to do extreme car breaking stuff, you should fit a rear locker. Many people with vehicles that are part time 4wd, fit auto lockers to the front axle, that way they can drive in 2wd on tar and not know about the locker and when they engage the front hubs, they have diff lock. People who do this usually swear by it and think it’s the greatest thing on earth. Unfortunately this is only because they don’t know better. The sudden huge improvement in offroad ability far over shadows the fact that a front auto locker is a total pain in the butt! It locks up and has a huge effect on the handling, this is because the wheels are turning at the same speed and fighting the steering. This not only increases the steering effort, but also greatly increases the turning circle. I’ve had a hilux which I bought with a front auto locker and there have been situations where the front diff locks up and I cannot get around a corner due to the wheels wanting to turn at the same speed and fighting each other, basically a seroius understeer situation. Then I have to put it in 2wd to be able to get around the corner. Running only a front locker also isn’t good for your front axle which is weaker than your rear axle, putting a lot of unnecesary strain on the front drive train. I know of a guy who argued that his front locker is lot better than a rear locker, after snapping 4 front side shafts, he agreed it’s not a good idea. In offroad situation a rear locker also works better as you usually need it when going up hills and then most of the vehicles weight is transferred to the rear axle, so you want maximum traction at the rear wheels.

After you have fitted the rear locker and you think you need more traction, you get to the difficult point where you need to decide if you want a front locker as well. At this point I would suggest you first upgrade your suspension and tyres as they offer more benefits if your already have the rear diff lock. A front diff lock will greatly improve the vehicle’s offroad ability, but not as much the improvement you got when you fitted the rear locker. To make full use of a front locker you’ll really be pushing the limits and when you start driving at that level, vehicle damage at some point is almost guaranteed. I’ve had 2 vehicles with front diff locks fitted and it was great, but those were very specialised vehicles built to take on the worst possible obstacles with ease. On the other side of the coin, when you do get stuck in a vehicle with 2 diff locks, you better know what you’re doing when it comes to recoveries.

My diff-locks:

You are probably wondering what experience I have of these different types of diff-locks, so here’s a list of my vehicles and what diff-locks I had in them. As you can see, in some of them I had more than one type of diff-lock as I experimented to find what works best.

-Series 2A landy – Rear welded diff

-Hilux 2.8D – Rear gearmax diff-lock

-Suzuki SJ410 – First a rear LockRight diff-lock, which I destroyed and then I welded the rear diff.

-Isuzu 280DT – Rear gearmax diff-lock

-Hilux Lexus V8 – Rear gearmax diff-lock and front LockRight locker, bought it like this, but front LockRight  I do not recommended.

-80-series 4.5 Cruiser – First I tried a rear EZ-locker which lasted 2 months before stripping it, that was replaced by a Detroit Locker which was very tough, but not switchable. Then I removed the Detroit and fitted front and rear ARB diff-locks and this is by far the ultimate diff-lock solution. The different diff-locks fitted to the cruiser, taught me more than any other vehicle of what works and what doesn’t.

-LR Discovery V8 – Rear ARB diff-lock

-Mitsubishi Triton – Rear factory diff-lock, replaced under warranty at 30 000km due to a factory assembly fault.

Some more diff-lock video’s:

Eaton G80 in action…note the rather violent engagement later in the video.

ARB Air locker demonstration:

ARB Air lockers increase strength:

ARB Air lockers and protecting the enviroment:

Air lockers and on-board air:

Maximising tractibility with air lockers:

How air lockers work:

Air locker comparison – ARB vs cheap copy:

Air Locker vs LSD vs Traction Control:

Part 1:

Part 2:

Installing an ARB Air locker: