Sorry if this is a little long. I want to relay the problem as accurately as possible.

After a short highway drive I noticed what I can only describe as a "funny feel" in my 94 AWD. It just wasn't driving the same. The next time I went to drive it there was a Grrrrrrinding noise when I put it in drive; Same thing in reverse. It wasn't a loud, destructive sounding noise; just one that you know isn't good. I unplugged the AWD controller to test it, and at first I thought the rear wheels were spinning as I was parked in an icy lot. Not so lucky. The same thing happens on dry pavement. It moves with the AWD disabled, but just barely. After reconnecting the AWD I drove home slowly, and there was a noticeable step/hesitation at the shift points, I'm assuming that that's when it locks the front axle.

I was I was thinking maybe the rear end was shot -- It's a limited slip and I don't have much working knowledge on what goes on inside of them -- so I put the parking brake on, put it in neutral but wasn't able to turn the rear driveshaft. I then unplugged the controller, started it and put it in drive (with the parking brake on and the van parked against a very solid pile of snow). What was unusual was the front drive shaft was turning. There wasn't any movement in the front tires, just the front driveshaft. Is there must be some kind of clutch inside? Does the rear differential have the same setup that could be slipping or is my transfer case toast? What is involved in the rebuild? BTW the fluid level is good.

Thanks of any info.

 

I would tend to guess that you have transmission problems and not necessarily xfer case probs. but I am not an expert. I don't think it is the rear end from what yo described.

 

No it's not the transmission, In 4WD it takes off and shifts really nice. It just won't go in 2wd with the 4wd controller unpluged. the front axle is dragging the van behind it.

 

Let's see if we can narrow this down a little for others to join in the discussion because I, for one, am confused about several of your statements. So far, "the van runs and shifts fine with the 4WD controller plugged in but not when it is unplugged". I am wondering which controller you are unplugging. The 4WD controller is under the driver's seat - is this the one you are referring to?

These vans have all time four wheel drive, a 30/70% split F/R under normal driving. When slippage is detected, the electronic solenoid in the transfer case is activated which locks the clutch pack, delivering a 50/50 split in intervals. Therefore, there is no 2WD drive capability so I'm at a loss as to what your problem may be. It sounds suspiciously like the transmission may be locking in overdrive but that is just a guess at this point. Any further details would be helpful.

 

If your front drive shaft is turning and none of your front tires are turning, that means:

1) Your front differential is shot. Gears are all busted up.

2) Or, one of the front axle shafts is broken.

When you disable the AWD, the T/C does what a regular differential would have done, it spins the side that is easiest to spin. In this case, it's the front axle, since the front differential is not putting up any resistance. The result is that it barely put any torque on the rear axle, and that's why the van barely moved when you unplug the AWD.

I would suggest checking your axle shafts. if they are OK, start "shopping" around local junkyards for a diff.

 

I'm unplugging the one under the seat. Your deduction of a broken axle makes sense. It's like a light just came came on above my head. Nothing looked out of the ordinary when I looked underneath, but I did see a broken CV boot that I put on my to do list. It may be broken there and I just didn't look to see if there is any movement when it was in gear. The movement in the front drive shaft is what had me confused. I thought there may a clutch inside the front differential that would allow movement at idle. Of course having to do this diagnosing in the dark isn't helping any. I'm planning to punch out early either today or tomorrow so I can get a good look in the daylight. Replacing an axle has got to be a lot cheaper and easier than a transfer case.

wish list: Lighted and heated garage

 

No, there is no clutch inside the front differential. If the front driveshaft is turning, at least one of the front tires ought to be turning also.

 

Thanks for the enlightenment. This is beginning to make sense. When I noticed the front driveshaft turning I was kneeling/lying down next to the van on the drivers side. I wouldnt' be able to see the passenger side from there, so I bet the axle was turning. I may not know much about t/cs and differentials, but I have enough sense not to crawl under there when it's running to get a better look! If the axle isn't broken it is most likely the front diff. I can't wait to get home and verify.

 

Update
I had a better look at things last night, aided by my Maglight. It looks like the front differential is shot. I read in another post that after removing the differential, the front axles can then be removed fairly easily. This would be a good opportunity to take care of the CV boots. I'm not sure if I should have this diff. repaired or start scouring junkyards for a replacement from a cost aspect. Does anyone know if these came with different gear ratios in the 4X4 model? I learned from previous problems with different sized tires how critical this is. Aerocolorado, Copper, thank you for your guidance on this

I Can't wait for the cold (along with these 12 hour workdays) to ease up so I can attack this project. Although I've only had it a short time I miss the Aero. It's the best all-around vehicle I've owned and I've owned many, both new and used. I now understand the loyalty the folks in this forum have for them.

At the risk of being a pain in the neck, does anyone know how the t/c separates the torque? I've looked at exploded views and assumed (what happens when we assume?) that the rear driveshaft was more or less direct driven, and clutch pack siphoned 30% of the power and directed it to the front, with the Electro-magnetic clutch delivering full power to the front when needed. Now I see it works some other way with some sort of voodoo happening inside there to ration the torque, and lock both driveshafts when needed.

 

Pbrunner:

It's done through chain and gears. The mechanism is really similar to what you have in the differential itself. You have two axles. If both axles have traction, the torque is divided 30/70 to the front and rear, respectively. However, once one axle looses traction (the front one in your case, I assume) that axle would be spinning freely, unless the clutch is applied, in which case it would force both front and rear axles to rotate at the same speed.

That's why when you plug in the T/C module under the seat, the van would move and shift. There is torque on the rear axle in that case. However, once you disconnect the T/C module, the clutch is off and the front axle is turning freely, therefore you have no torque on the rear axle to move the van with.

Now that brings us to the next question, what really happened with your van. I suspect that there is something wrong with the speed sensors in your T/C to begin with. Take them out and measure the resistances between the pins. They should be about 1000, 2200 and 3200 ohms between different pins. The reason I suspect that is because of the obvious lockup of your T/C clutch that caused your drivetrain to "wind-up."

When the clutch is applied (perhaps by a false signal) the front and rear axles are forced to rotate at the same speed. However, the tires and gear ratios are never exactly the same between the two. After a while, this disparity would cause the gears in the two differentials to work against each other. Think of it as one fast walking guy trying to hurry a slow walking guy along at the same speed. On snow and ice, this doesn't hurt anything, since the slow guy can slip and be dragged along. However, on dry asphalt it's different; there is no relief by slipping, so there is a lot of stress on the gears which would lead to failure of the weaker axle, which is the front one in this case.

So, even after you repair the front differential, you would still need to diagnose your T/C to make sure it's not the cause of the trouble.

I'm still willing to bet that one of the shafts broke inside your differential. If that's the case, it'll be fairly simple to repair. It's hard to imagine the gears all gone. Or you can just get a used Dana 28 differential from a junkyard. But make sure you change fluids (Mercon) and put in new seals before you put it back in the van.

Good luck

 

Thanks again for the great info.


As a sidenote, is there any way a mod can fix my typos in the subject line so others can learn from my experience?

From mistakes comes experience and from experience comes wisdom

 

Normal men learn from own mistakes. Wise men learn from other's mistakes.

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