Testing the 4WD

[moggy1968]

Post script
Only a full time 4wd has a centre differential, a part time 4wd doesn’t need one because on pavement you should only be in 2wd and then engaging 4wd mechanically locks the front and rear together for off road use.

 

[Dave2000]

Just to clarify.....

When the rear diff on the 80 is locked the drive goes equaly to both wheels regardles if one is on glass and the other on tarmac.

The same applies to the front axle as well.

Regards

Dave

 

[Dave2000]

I note the OP said he had drive to the rear and then asked if he should engage the centre diff, surely the centre diff has to be engaged to get the rear to lock?

In which case he would (should) have solid drive to both rear wheels and solid drive to one of the front wheels, i.e. the front wheel with least traction would be spinning.

Regards

Dave

 

[moggy1968]

Just to clarify.....

When the rear diff on the 80 is locked the drive goes equaly to both wheels regardles if one is on glass and the other on tarmac.

The same applies to the front axle as well.

Regards

Dave

That’s the same in any vehicle on any axle equipped with an axle locking diff, not just an 80.
What we haven’t established from the op is what, if anything, he has locked. It looked as though none of his diffs were locked, centre or axle.

 

[Dave2000]

Yes I know, but terminology was going awry, so felt it necessary to clarify.

Regards

Dave

 

[moggy1968]

I note the OP said he had drive to the rear and then asked if he should engage the centre diff, surely the centre diff has to be engaged to get the rear to lock?

In which case he would (should) have solid drive to both rear wheels and solid drive to one of the front wheels, i.e. the front wheel with least traction would be spinning.

Regards

Dave

No, if you have locked the centre differential you only need one front and one rear to be spinning to be stuck, your just locking the front and rear together, not across the car. for both rears to be spinning you need a rear axle diffloc as well.

 

[Dave2000]

I know how it all works, I was pointing out the rear diff lock does not engage unless the centre lock is engaged first. He said he had rear wheel drive, I assumed he meant he had engaged the rear diff lock, and I was then asking how he did that without engaging centre first?

Regards

Dave

 

[moggy1968]

I know how it all works, I was pointing out the rear diff lock does not engage unless the centre lock is engaged first. He said he had rear wheel drive, I assumed he meant he had engaged the rear diff lock, and I was then asking how he did that without engaging centre first?

Regards

Dave

Ah with you,
from the way it read it looked as though you were expecting the centre lock to also lock up the rear (a common misconception).

 

[Dave2000]

Ah with you,
from the way it read it looked as though you were expecting the centre lock to also lock up the rear (a common misconception).

Nah, BTDT, LC electric lockers with CDL button, ARB air lockers in my competition Discovery, got it covered.

Regards

Dave

 

[Steveindar]

So it's getting close to mud season and I really need to nip off some time to sort out the 4WD.
I see in the manual there are various options of transfer case coupled to transmission according to the engine mounted.
I have tried to find the codes stamped on the casings but just can't find them. Where are they located on the transmission and transfer case?
The vehicle specs say there is a 442F transmission mounted. I need to know whether it is coupled to a full time 4WD transfer case, HF-2A, or a part time 4WD transfer case, HF-1A.
Engine is 12 valve 1HD-T.
So where to look to find the various markings for HF-2A or HF-1A on the transfer case?

Cheers
Steve

 

[Steveindar]

So it's getting close to mud season and I really need to nip off some time to sort out the 4WD.
I see in the manual there are various options of transfer case coupled to transmission according to the engine mounted.
I have tried to find the codes stamped on the casings but just can't find them. Where are they located on the transmission and transfer case?
The vehicle specs say there is a 442F transmission mounted. I need to know whether it is coupled to a full time 4WD transfer case, HF-2A, or a part time 4WD transfer case, HF-1A.
Engine is 12 valve 1HD-T.
So where to look to find the various markings for HF-2A or HF-1A on the transfer case?

Cheers
Steve

Again, it's been a while. So at the end of July after a full mud season with no 4x4 and several tows later I got under the car. Seems there have been some "modifications" done by the PO. The transfer case currently mounted is for the part-time 4wd version with the short extension housing to the rear prop-shaft. So that explains away the 2wd only. What wasn't working was the CDL actuator. After loosening the mounting bolts enough I lowered the gearbox and transfer case enough to get access to the actuator. Stripped out and opened it was solid rust/gunk/mould etc. Managed to get a working 2nd-hand unit, installed and.....Dammit, 4wd is back when the CDL is activated! So now just waiting for the next mud season to start to try her out. Slowly, slowly learning stuff and wondering why I didn't do this sooner.

 

[Steveindar]

So leading on from the above post, does anyone now what "other" manufacturers free-wheel hubs will fit the old girl? Pajero's seem to be plenty on the market, but Toyota/Aisan not so.

 

[PeterLC]

Ah, the old diff discussion. Open diffs don't split power equally to both sides, and the fact that they redirect power to the side with the least traction is simply because they spit TORQUE in two EQUALS. In some cases this may make a difference in understanding what is happening.
With three open diffs, central front and rear and one rear wheel in the air, the torque to the rear wheel on the ground will be the same as to the one in the air, so very small, just the drag of the brakes. Hence there will also be a small torque to the rear output of the central differential and so also to its front output and that will end up as the same torque on both front wheels. You will notice it when you do the test, the car may want to move slightly when you spin the wheel in the air. If we have a front wheel in the air too, only the wheel with the least drag will spin as all others get the same torque and that is not enough to spin any of them.

 

[Steveindar]

Ah, the old diff discussion. Open diffs don't split power equally to both sides, and the fact that they redirect power to the side with the least traction is simply because they spit TORQUE in two EQUALS. In some cases this may make a difference in understanding what is happening.
With three open diffs, central front and rear and one rear wheel in the air, the torque to the rear wheel on the ground will be the same as to the one in the air, so very small, just the drag of the brakes. Hence there will also be a small torque to the rear output of the central differential and so also to its front output and that will end up as the same torque on both front wheels. You will notice it when you do the test, the car may want to move slightly when you spin the wheel in the air. If we have a front wheel in the air too, only the wheel with the least drag will spin as all others get the same torque and that is not enough to spin any of them.

Thanks for the explanation Peter, now I'm looking for some freewheeling hubs that will fit.

Any ideas?

Steve

 

[PeterLC]

Steve, you got me confused. If understood that you have AWD trucks, so they have a central differential. Add free wheel hubs and there will be no torque possible towards the front wheels, so no torque on the front output of the central diff, no torque to the rear output, no torque to the rear wheels. You will need to permanently lock the central diff in order to move your truck. The result will be that all parts in the front axle will move as before, just no torque transmitted. The torque formerly transmitted to the front wheels, now goes to the rear wheels, i.e.douled torque there. Nothing to gain by adding free wheel hubs Steve (if you have a central diff).

 

[frank rabbets]

Do Toyota do freewheeling hubs for the 80. I would have thought the 80 was designed for permanent 4wd. Cutting drive to the front wheels would alter cornering characteristics and increase rear tyre wear. With a part time 4wd you could have freewheeling hubs to stop the wheels turning the front axle components, other than that I can't see advantage.

 

[Chris]

I could well be wrong - it wouldn't be for the first time, but I do believe there was an iteration of the 80 that did not have a centre diff. It had a transfer box, but not a diff and these were fitted with FWH. The 105 certainly has this arrangement on some models.

With a UK spec 80 and FWH you would get drive because of the viscous coupling, but anything more than a mild slope and you slow to a halt. With the CDL engaged you'd be off again in rear wheel drive only. I have tried this and it's awful. If you have a farmer's spec 80 with no VC then clearly you'd get no drive at all until you locked the CDL. Which is why I retro fitted a VC to my GS.

Summary. If you have a transfer box only model then you'll already have some form of disconnect in the T box or hubs or both. If you have a full time 4x4 80 then leave it alone. It's an advance on the former design. Don't go backwards. There are no gains to be had in economy. I tried it for almost 6 months and consumption went up.

 

[frank rabbets]

There's a theory that a driven wheel causes less friction and loss than one being pushed round by the road so I'm not surprised by Chris's observations on economy.

 

[Chris]

It also felt like an effect driven by weight transfer Frank. as we know, when accelerating, WT is to the back. On a heavy old tank like this, it felt like it was bogging down a bit and needed a bit more right foot. With the front axle working, there is more of a push me - pull you effect going on where the car is simply more balanced in terms of drive. It's much harder to spin the wheels of a rear wheel drive car as we know and dead easy to spin the wheels of a front wheel drive car. But together, mated through a VC the two work harmoniously.

 

[chapel gate]

Yes, I'm pretty sure some markets were offered the 80 with "selectable four wheel drive".