Testing the 4WD

[Steveindar]

Hi All,

Been a while since my last post. Still have my original HZJ 81 and have recently supplemented that with another HZJ 81, but this with a turbo.
Was checking the undercarriage and the general workings and thought to check whether the 4WD works. So I jacked up the front right and left rear, started up and put her into drive and...only the rear wheel spun! Thinking I had something wrong, I did the same to my older cruiser and..only the front wheel spun! Confused!
Am I doing something wrong? Both cars have full time 4WD with no free-wheeling hubs so I would expect a wheel at each end to spin.

S

 

[Chris]

Well all 4x4s are only 4 wheel drive when all 4 wheels are on grippy ground. Forget lockers etc and traction control. A 4x4 will put all drive to the wheel with the least resistance. This may mean that despite 2 wheels being off the ground, that the front wheel somehow has more resistance than the rear. It could be that the handbrake is on or that the brakes are binding slightly so the front wheel is the easiest to turn. Or it may meant that you have some sort of disconnect on the front prop or drive flanges. I'm not altogether up to speed with the 81 drive train

Edit - I realised it was the rear turning and edited the post but didn't change the bit about handbrakes. So it might be the front brake binding or as Rich says, an LSD or something.

 

[clivehorridge]

Only applying some logic here, but I suppose the one that had the front wheel spinning may have an LSD at the rear, forcing the drive to the wheel with least resistance at the front.

I think LSD’s are common or an option on JDMs.

 

[frank rabbets]

Well you defo have drive to the rear so you could put the handbrake on or put the rear wheel on the ground and SLOWLY lift the clutch pedal to see if you have drive to the front as well. If you only have drive to the rear you'll feel the car trying to drive forwards.

 

[Chris]

Putting it drive might suggest it's an auto.

 

[frank rabbets]

Foot SLOWLY on throttle then.

 

[white90]

Hi All,

Been a while since my last post. Still have my original HZJ 81 and have recently supplemented that with another HZJ 81, but this with a turbo.
Was checking the undercarriage and the general workings and thought to check whether the 4WD works. So I jacked up the front right and left rear, started up and put her into drive and...only the rear wheel spun! Thinking I had something wrong, I did the same to my older cruiser and..only the front wheel spun! Confused!
Am I doing something wrong? Both cars have full time 4WD with no free-wheeling hubs so I would expect a wheel at each end to spin.

S

Won’t work unless you lock the centre diff

 

[MarkW]

Finally...............…

 

[Steveindar]

What if I jack all the wheels off the ground then put power, with no resistance on the wheels should i get an even front/rear power split? Or depending on which wheel turns then block that one and see what happens?

 

[Steveindar]

So White90, you say lock the center diff to get even power front and rear?

 

[Firewout]

So White90, you say lock the center diff to get even power front and rear?

I think you should have at least one wheel spinning in front as well.

 

[white90]

Center diff acts like an axle diff, it needs resistance both ends to work, if you jack one front and one rear up and drive it may only spin one wheel, either the front or the back, lock the centre diff and it should drive both ends.

 

[white90]

I think you should have at least one wheel spinning in front as well.

He’s only jacked up one wheel so it won’t drive until the centre diffs locked

 

[Chris]

81's don't have a centre VC then I guess.

 

[white90]

81's don't have a centre VC then I guess.

The fact that only one wheel turns when jacked up and driving suggests it doesn’t, also forgot to say you need the handbrake off when testing it.

 

[Iwan]

I seem to remember reading that the 1990 to late 1992 80's didn't have the VC and it was introduced in the 1993 80 series onwards and apparently the 7 pin mod doesn't work on a pre 93. Not sure what that is as I've got a 1991 mongrel!

 

[Dave2000]

The resistance needed to transfer drive from one side of an open differential to the other can be as little as resting your hand on the tyre.

As per @Chris's post assuming no VC, the 80 will only move if all four wheels have traction, jack one and car does not move.

Engage centre diff lock and now just two wheels front or rear need to have traction to move car.

Regards

Dave

 

[Steveindar]

Got around to actually checking the 4x4 yesterday by driving into some slippery stuff. Seems only the back diff was under power as it slid all over the place with no help coming from the front. Does that mean that I have to engage center diff to get front traction? That's not the way it works in SWAMBO's 80, if you hit the smelly stuff there's always a front wheel chucking mud over the mirrors.
What to do? I don't want to start stripping out transfer cases yet.

 

[clivehorridge]

As said above, with lockers open, power will go to the wheel(s) with least resistance, that’s why there’s lockers, to direct the power to wheels with grip.

One rear wheel spinning in mud, the truck will go nowhere.

CDL will then direct 50/50 to the front axle.

If then you have one front and one rear spinning, the truck will still go nowhere.

In the order of rear axle first, the axle diff locks will divert power to the non spinning wheel on each axle, simples.

After locking all the diffs, all 4 wheels spin, then you need a tow, or a winch.

I suspect there’s nothing wrong with your 80, if the diff locks are operating properly, nothing you’ve written suggests they’re not.

The only variant to the above is the effects of a torque converter (TC) (which mine doesn’t have) so it’s hard for me to comment. AFAIK, the TC has the effect of the Centre diff behaving like a limited slip diff, where yes, more power will go to the front axle, before having to lock it up.

All JMHO of course,

 

[moggy1968]

In a full time 4wd (or anything 4wd actually)If you had power being transmitted equally front and rear you wouldn’t be able to go round corners very well and the transmission would go boom. To get around this problem you have a centre differential which works the same as your axle differentials allowing the wheels to turn at different speeds when cornering. As has been explained well above, if you have a centre differential, rather than some sort of centre viscous coupling, you would need to lock that to stop all drive going to the wheel with the least amount of grip (in your first example the wheel in the air) what isn’t clear is whether you have indeed applied the centre differential, if you have and drive is going only to the rear, you have a mechanical problem. If you haven’t, you have an operator problem!