Why I'll be installing a differential lock

Welcome to class kiddies. This may be obvious information for some, but useful for others.
First lets explore why all cars have differentials:
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The landcruiser/patrol/pajero has a rear limited slip differntial (LSD) and an open differential at the front.
In the simple examples above where one wheel is on a slippery surface, a LSD is usually effective in maintaining progress.
It continually comes as a surprise to most people that find their expensive 4WD is rendered imobile when traction is lost on opposing corners. Examples of this include any occasion where two wheels have more weight on them, like when climbing an uneven step or undulating surface.
It gets a little more complicated than that as well. Due to the design of an open differential, these two pictures below illustrate the bigger problem at hand... when all the power goes to the wheel in the air, that means NO driving force is going to the wheel that is on the ground.

Any time you have a wheel in the air, you've effectively got a 2WD vehicle. Now, consider that all the force required to continue motion up the hill is only driving the back wheels, that's sometimes more traction than the rear wheels combined have and this scenario will often push the drive out the easiest path. Illustrated below:

See how the left front wheel is off the ground (meaning no front drive at all) and the resulting drive going to the back diff only results in spinning the rear left wheel. This calculation all results in no drive going to the ground.

Even one axle with a differential lock makes a huge difference as it doesn't allow this 'cross axel' drive loss to occur. You all understand now? Good.

Once you've decided you want a diff lock a few more questions are put on the table:

What kind?

There are many different kinds of diff locks with many pro's and con's. One of the most common is an air operated locker. These are typically the most expensive option, but they do have the ability to lock and unlock by driver command. The system relies on positive air pressure to hold a locking mechanism in place for duration of the lock. The only problem with this design is it's complexity. It requires air lines to be plumbed into the differential housing, running air lines to a compressor, dash switches, pressure regulators etc. 

The other options are two kinds of automatic lockers.  One is known as a Detroit / Eaton locker which has a interesting set of worm gears that manage to allow a wheel rotation or two before locking the diff. Obvious advantages included lower cost, automatic operation and seemingly unchanged on road performance. I have heard though that you can cause them to lock unintentionally in harmless onroad scenarios like roundabouts - which can have surprising consequences on a wet day.

The other option is an Aussie Lokka - as you guessed, designed and manufactured in Australia.

This is an interesting contender as it's more of an automatic UN-locker. It's locked all the time unless you cause differential action such as turning a corner.

The biggest selling point is the warranty - they will cover it for some 3 years regardless of it's use. You can use it in competitions, super huge power input - no worries. That says to me that reliability must be outstanding.

Which end would I fit it?

There are die-hards that tell you that if you're going to fit a diff lock, you must fit it in the back diff. I challenge these people. Toyota's typically have quite good limited slip differentials in the back diff, so I propose putting the Lokka in the front and leaving the LSD in the rear. Best of both worlds. Excellent on-road manners as it's all factory and epic traction and power delivery when you lock it in 4WD. The funny thing about the picture above with the Jeep, is that it has a rear locker. This guy removed the factory LSD and replaced it with a locker. It's only giving him a little more help in this scenario - installing it in the front would have been smarter. You can see that his right hand front wheel has excellent traction - pity it's receiving no drive.

If it was a constant 4WD vehicle, I would be inclined to use air-operated diff locks as you can't unlock the hubs and you can't disengage 4WD. Our 4WD choice is a part time 4WD - If there were any disadvantages in our Lokka choice, we can simply unlock the hubs and the disadvantages are gone...  Also being around 1/3rd the price is a great help.

This brings me to the topic of Maxtrax. I've had them for years and they are awesome, but they have one downside which is totally user related.

1) You only decide to use them once you've exhausted all other options. Sounds stupid I know, but they work best before you're down to your sills in mud or sand.

2) Usually, after you've left it too late due to the above point, you often only have one front wheel, and one back wheel spinning. Again due to the 'cross axle' condition I describe earlier in this topic.

3) Because you're now down to your sills in mud/sand you struggle to get them in front or behind the back wheels. So, your front wheels are usually the best bet.... however only one of them will spin!

So do you see now how it's all connected? Maxtrax work best with a diff lock.

This is just clarification of one of the reasons I'll be installing a front diff lock! It means climbing up the very occasional step like this on the road of bones should be slower and safer.