Need Help Analyzing AWD system

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livelarg

livelarg

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When I bought this my 1991 80, the AWD was a little confusing. †he previous owner said that the guy he bought it from (got it?) had converted the AWD system to be a part time system. Ok, that is all I know about what was done to it.
This is what I know about what it actually does.
It has Aisen manual hubs.
I have to drive with the CDL button in Locked position. The truck only drives when CDL is locked. when it is not Locked, the whole system seems to be in neutral, No matter if the hubs or locked or not.
I want to get back to the normal AWD set-up. I don't know much about the AWD system, though I have read about it here on ih8mud. What would be changed to make it work the way mine does, and how can I fix it?
Thanks for any info you can give me.

Thanks
Kent:cheers:
 
You will need to convert your transfer case back to full time. Did the PO install Marks part-time kit? Perhaps someone with a full-time case would like to swap with you.
 
I think he still has the fulltime case, he just has to drive it with the cdl button depressed to move.

First, it's not AWD. It's full time four wheel drive. There are differences betweent the two, but that's a different thread.

If you want to be in full time four wheel drive, lock in the front hubs and turn off the center diff lock.

With your front hubs unlocked, the center diff must be locked to transfer power to the rear wheels. Otherwise it acts like a standard vehicle axle with one tire up in the air; the differential sends all power to the end of least resistance. In that case it's the elevated wheel, in your case it's the front axle.
 
shocker said:
If you want to be in full time four wheel drive, lock in the front hubs and turn off the center diff lock.

With your front hubs unlocked, the center diff must be locked to transfer power to the rear wheels. Otherwise it acts like a standard vehicle axle with one tire up in the air; the differential sends all power to the end of least resistance. In that case it's the elevated wheel, in your case it's the front axle.
Click to expand...
Only problem with that is, he said it won't move if the CDL is unlocked, with hubs locked or unlocked. :doh: :grinpimp:

livelarg- Stating the obvious here, but you do hve the front driveshaft hooked up, right? It goes from the tranfer case to the front axle.
:)
 
firetruck41 said:
Only problem with that is, he said it won't move if the CDL is unlocked, with hubs locked or unlocked. :doh: :grinpimp:
Click to expand...

Ahh... missed the part where he said it still wouldnt move if he had the hubs locked.

I'd look for the front driveshaft too. Maybe the front gears were never put back in? Front flange worn? Missing front axle?
 
Thanks for all the ideas.
I do know that the front driveshaft is installed :)

I lifted all 4 wheels off the ground and did some testing. and this is what I found out.
With the CDL ON. The back wheels work and the front driveshaft spins, But the front whells don't drive even when the hubs are locked. The driveshafts seem to be going the same speed
The the CDL OFF. The back wheels spin, but very slowly, and when you put any resistance to them, the back wheels stop. The front driveshaft spins alot faster than the rear.
Knowing what I know about the system, that seems to be the way it should work, but of course the front wheels should be spinning.
So my guess is that somehow the front axles/hubs are disconnected from the drive shaft . I am wondering if the gears from the front differential have been removed or disconnected? That would explain the way it is working now. Any ideas on that?
So for a guy that has never looked inside of a differential. How should I go about checking it out?

Thanks
Kent
 
Sounds like the birfield and hub spline engagement isn't happening or the front diff is toast.

I would start by pulling the hubs. If everything looks OK, pull the axles and diff.
 
before opening up the diff and dealing with the gaskets/seals etc, maybe you can open a hub and see if the axles are there and spinning? Might be easier?
Is it possible that the manual hubs are just busted?

add: overlapped with Cman
 
e9999 said:
before opening up the diff and dealing with the gaskets/seals etc, maybe you can open a hub and see if the axles are there and spinning? Might be easier?
Is it possible that the manual hubs are just busted?

add: overlapped with Cman
Click to expand...
The hubs could be busted.
I need to take off the hubs anyway to replace my brake discs. I can just look at them then.

My truck has been this way since I bought it, so They must have been like this for quite a while. So now I don't have 4wd at all. I hope it is just the hubs, that would be the easiest to fix.
:rolleyes:
 
The manual locking Aisin hubs use a spring to push/pull the ring gear in or out. If too much or not enough grease is used to lube the hubs, the gear could be bound up and stuck in the unlocked position. As previously mentioned, check the hubs first. Both of them must be working correctly. If only one of them is actually locking, then the power still goes to the unlocked side due to the nature of an open differential (assuming the previous owner didn't install a front locker, different from the center locking diff).

Since you've verified that the front drive shaft does turn when you lock the CDL, but the wheels don't turn regardless if the hubs are locked, technically anything could be broken in the front axle from the hubs, outer axle shafts, birfield joints, inner axle shafts, and differential (everything between the front wheels and front driveshaft). However, if anything else were actually broken I would expect there to be scary noises. I am thinking that it's just the hubs sticking or are incorrectly assembled. The factory Aisin hubs are quite strong and tuff to break. They are all metal construction.

Otherwise, the setup you have is actually rather nice. It will save some wear and tear on the front axle parts. While everything still spins, it's not under load and has less stress on it when 4wd is not needed.
 
Last edited:
mnwolftrack said:
Otherwise, the setup you have is actually rather nice. It will save some wear and tear on the front axle parts. While everything still spins, it's not under load and has less stress on it when 4wd is not needed.
Click to expand...

thanks for all of the info.
The only problem with the set-up is that I don't have 4wd at ANY time. So I need to find the problem.
The hubs may be the problem, but it seems odd that both would be messed up. But I am going to take them apart anyway when I replace the brake discs. then I will also check everything else.


Landtank, I would like to keep the aisen hubs if I can, that way I could turn off the front wheels if I want to, maybe save on a little gas.

Thanks
 
If one hub isn't engaging then it will appear that you aren't getting any power to the front axle, when in fact you are. The problem is all your power will be going towards the hub that isn't engaged. It's like constantly having one wheel in the air.
 
livelarg said:
I want to get back to the normal AWD set-up.
Click to expand...


livelarg said:
Landtank, I would like to keep the aisen hubs if I can
Click to expand...


I only mentioned the flanges because of the first quote. So if you have changed your mind then you'll need to first make sure those hubs are good. I think I have read on here that there was an issue with the stub axle length and those hubs. It's not a setup that I am interested in doing so I can't be more help.
 
landtank said:
I only mentioned the flanges because of the first quote. So if you have changed your mind then you'll need to first make sure those hubs are good. I think I have read on here that there was an issue with the stub axle length and those hubs. It's not a setup that I am interested in doing so I can't be more help.
Click to expand...

The later FZJ80 stubs are longer causing the problem, the Asians fit FJ80s. If one hub is not locking you won't have front drive, unless you have a locker. It's easy to remove the six small bolts and pull the outer part to confirm that their working.
 
livelarg said:
thanks for all of the info.
The only problem with the set-up is that I don't have 4wd at ANY time. Thanks
Click to expand...

Right--I meant your setup is actually nice (in my opinion) once the system is working the way it should have been with locking hubs installed. Perhaps they put the wrong hubs on too. If you do a search on fuel economy (or lack of it) or a search on part time 4wd, I think the consensus will be that part time doesn't offer better mileage. But I will say that it offers less wear and tear on the front axle because there's no load. My '85 pickup has a slightly worn front driveshaft, and there's a huge difference in the amount of vibration between having the hubs locked and the transfer case in 2wd vs. the hubs locked with the transfer case in 4wd (in 2wd with the hubs UNlocked, there is no vibration). There is a lot more vibration in 4wd because of the load on the front driveshaft and the fact that the center diff, aka transfer case, is always locked. I leave my pickup's Aisin hubs locked all winter long even if only in 2wd so I can shift the transfer case in or out of 4wd on the fly. There are plenty of times when a sudden slippery patch comes up out of no where.

The front axle assembly can be rather expensive to have rebuilt if you don't know how to do it yourself, so the less wear and tear, the better in my opinion.
 
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