4WD Systems - How they work.

OK.
How about using a GXL as an example.

So the centre diff splits drive 50:50. - Is this usually engaged when 4H or 4L is selected.

Diff lockers split the drive again?

The centre diff splits the drive forward & rear, but not necessarily 50:50, it works on the same principle as any other 'open' diff, it will provide drive to the wheel(s) with the LEAST traction.

Think of the GXL as an 'all' wheel drive, like a subaru or territory. The centre diff lock simply converts the 'All' wheel drive 100 GXL into a true '4' wheel drive GXL.

Diff lockers lock the left and right axles together, that way regardless of which tyre has what traction they both spin (drive) at the same rate. Air lockers are switched on when needed, and HAVE to be switched off when not, auto lockers are 'on' all the time and 'auto unlock' when needed (turning etc).

First, a very simple explanation on how a diff works and what it does.

A diff allows drive to be transmitted to both wheels on the same axle, and at the same time, allowing the wheels to travel at different speed and distance.
A centre diff allows drive to be transmitted to both front and rear diff at different speed and distance.

GXL is a constant 4wd. It has a 3rd diff which allow the vehicle to be driven on the road with out getting transmission wind up.

Power is delivered to all four wheels, but if any of the 4 wheels are off the ground or can spin, then all the drive will go to that wheel. The vehicle will not go anywhere.

With the centre diff lock engaged drive still goes to all four wheels. If a wheel can spin or is off the ground 50% of the drive will be lost through that wheel.
The other two wheels that have traction will drive the vehicle.

Even with the centre diff lock engaged and a wheel on the front and back loose grip at the same time, all the drive will be lost.

The centre diff lock can be locked in high range by the push of a button. This puts the vehicle into 4wd and should not be driven on a hard surface.

When low range is engaged the centre diff lock is lock by the shifting of the transfer leaver. Again the vehicle should not be driven on a hard surface when in low range.

The reason why vehicles should not be driven on a hard surface when 4wd is engaged because of transmission wind up. Transmission wind up accrues when a vehicle is driven on a hard surface and then has to make a turn.
The inside wheel on the front or rear diff will make a smaller radius than the out side wheel on the same diff. The front and rear diffs will also travel different distances If the vehicle continues to drive, the transmission could break.

A diff lock, as the name implies will lock the diff and both wheels on the same axle will turn at the same rate. if all three diffs are locked ( front, rear and centre diff) all 4 wheels will turn at the same rate. It would be almost impossible to turn the vehicle in this mode with out breaking some part of the drive train.

This is a very simple answer and there are a few variables that will only confuse things

What ever vehicle you decide to get, do a 4wd driving course to find out how your vehicle works.

Wayne

Thanks for that.

I found a link directly explaining diff lockers, which was useful.

o4dirt it probably hasn't been explained much above but the comment was made about the contact with the ground with a lot of the 4bys.

Where you don't have equal contact all round (and traction of course), you need lockers more than is the case with thos enjoying contact. Look for trouble where you have wheels in the air crossing holes or rocks ans spinning madly. If you have flexibility and wheel travel with suspensions you can avoid problems better. IFS does not guarantee better wheel travel and wheel contact with articulation, quite the contrary.

Gday Kingo

I'm ion the same boat as you, and traction should be the same with in auto or lock, as in auto they should automatically lock. Going downhill with engine breaking shouldn't unlock them, as the practice of driving backwards to unlock has the wheels revolving backwards, shaft trying ro be stationary (but with very little resistance) With this in mind, going down hill will have the front wheels trying to go faster than the tailshaft, which is the opposite of goeng in reverse to disengage them........Therfore they would be at greater risk of disengaging while going forwards..........maybe there is someone out there who can explain this and how they work better...

Hope this did'nt spread too much dark on the subject...

Cheers Andrew

....should read "risk of disengaging while going forwards (once the fun is over and 2wd is selected)

Kingsley,

You have got your self stuck, the vehicle is not moving. Easy to get out the vehicle moving again, engage 4wd. Auto hubs will engage and the vehicle will be on the move again. Wrong!!!

The only thing is that the vehicle has to be moving to engage the auto hubs. So if you are already stuck the auto hubs will not come in until the front wheels move.

If you are going to go 4wdriving it is just as easy to lock the front hubs in, you can still drive in 2H on the black top but when extra traction is required the auto hubs are ready to go.

Wayne

Gday Wayne

In the GU, under the car, wheels on the ground, turn the front tailshaft about a third of a turn and they lock, so engaging 4wd while stuck in 2wd will lock the front hubs in (I'd be doing it very gently with the clutch though, I think they break easy!

May be different on different makes or models

Cheers Andrew

Wow, that simplified things! Hence the simplicity of manual hubs.

Thanks fellas!

Wayne, I reckon you are on the money, having re-read the manual. The implication is that "fore-warned is for-armed". I have intuitively used the transfer lever to "snatch" into 4H when suddenly coming into a slippery or sandy patch. It works just fine and you can feel the front wheels pulling the vehicle through. From your explanation I won't change my procedures except that I know that if I am in for a day's driving in a mixture of sand/mud and good surfaces (including blacktop) I can safely lock the hubs before hand. The only problem of course is that I have to get out of the vehicle to do that and also to unlock when completed.

I enjoyed using the dial selector on my previous Pathfinder. I presume the Patrol will go over to that system one day.

Kingo

I have also heard that the auto hubs MAY disengage in reverse or if you need to rock the vehicle to build momentum as in if you are stuck in sand

Bware,

I thought that the Patrol was classified as "Part-time 4WD" because it normally only drives the rear wheels unless you physically pull the lever.

Kingo

Kingsley, I don't know; I was questioning the question.
Don't make it any harder than it is... Or did I do that LOL

Bware.

Wayne has answered my confusing question. (Thanks)

I was trying to find out is what makes the cruiser and patrol better than other models in off road performance and how their 4x4 systems work.

When reading magazine reviews and talking to 4x4 owners the Cruiser and Patrol seem to be at the top of the list when it comes to off road ability. For example, in the latest 4x4 monthly they take six rigs up Cape York and the review seemed honest to their word. To throw these things down the gauntlet straight out of the box and onto one of the hardest treks in Aus is a big ask. The Cruiser and Patrol end up on top with the other 4x4's with the fancy traction control systems.
So hence my question about the 4x4 system on these two and what makes them more capable.

In regards to the diff lockers, how necesasary are they to have? I mean if I bought a rig tommorrow, should I drive it straight into a 4x4 shop and get them to fit them? Or can you get away without them by negociating trails to minimise wheels in the air.
If my plan is to build up a confident and capable off road rig what order should accesories be bought in. I'd love to do it all at once but the budget simply aint that big.

I will endevour to join a 4x4 club to gain experience before doing anything on my own.

Thanks for the input so far.

G'day one4dirt,

I have an '02 GU Patrol (TI). It is magnificant off and on road. So far, I haven't been stuck once and it is bog stock. It did the whole of Moreton Island in 4 high as nothing there was strenuous. Also recently been to Cityview 4x4 park in Beaudesert and Crystalvale 4x4 park at Crystal Creek. I have found the standard features of the vehicle to be fantastic. I am probably not as serious as other people in this forum but I put it over the extreme track at cityview (jeepers decent) and it never missed a beat nor did it even bottom out.

Admittedly the GU Ti's come with a vaccume lock diff in the rear which can make it much easier to negotiate the slippery mud hills. I however conquered most of the climbs at crystal creek without using the locker as I was challenging a mate in his rangie!

The standard setup has certainly sufficed for me as we actually purchased the vehicle for a family car. With the standard suspension the car drives like a sedan on the road and it certainly attempts the moderate stuff with no problems at all. I am not into rock climbing or submerging the car in 5 foot of mud bog holes so it does everything i am interested in.

Besides, I dont really attempt the crazy stuff coz I am too lazy to buy the winch let alone walk up the hill first with the cord!

Hope I could be of some help ;-P
Cheers Tom.