Center differential problem?

[Turboturd]

I already tried posting about this on Talk, but haven't received much help. Essentially, I rebuilt my AWD trans, I did a Jack's stage 2.1 except that I didn't modify the center diff. Now the rear wheels aren't spinning while driving. Neither is the driveshaft. I removed the TC, it looks great, and spins fine (I used another output shaft I have laying around. The output shaft from the trans and the TC show no signs of wear or damage to the threads.

So, do I have a center diff problem? Or maybe the viscous coupler is bad? What should I try next to determine what is wrong?

There were no bad noises from the trans while driving, it works fantastically, it's just FWD!

Also, the trans is a 90 model, but I have another 92 trans at home, will the center diff and viscous coupler swap?

Any help appreciated,
Connor

 

[donniekak]

So when you drive the back wheels are locked up? That is not spinning. For the driveshaft to not spin while moving, the rear end, and transmission have to be broken.

 

[Turboturd]

No they aren't locked up, if you spin the rear wheels they turn fine, and the driveshaft rotates when you turn the rear wheels. There is a problem somewhere between the center diff and the transfer case.

What I meant by not spinning is that they are not turning when the car is in gear, it is essentially a FWD car and is driveable as such. On a lift, with the car in gear, only the front wheeels spin

 

[Canadian_CD9A]

No they aren't locked up, if you spin the rear wheels they turn fine, and the driveshaft rotates when you turn the rear wheels. There is a problem somewhere between the center diff and the transfer case.

What I meant by not spinning is that they are not turning when the car is in gear, it is essentially a FWD car and is driveable as such. On a lift, with the car in gear, only the front wheeels spin

Your viscous coupling sounds like it's worn out. The viscous is the limited slip function - without it, the wheels with the least resistance will be the ones being powered.

 

[4g63t]

Call Jack's since that is where you go the parts from?
I know my car goes into FWD mode when i have broken rear axles.

Either way the CD is easy to take out with the transmissions still mounted on the car. There are tons of threads on it

 

[donniekak]

When you launch a Dsm without a welded diff usually the right front tire spins. If you don't have a welded diff there is no way your car is still driving around with no power to the rear wheels. The vc would be burned up by now, and the car would barely move in gear.

 

[Turboturd]

When you launch a Dsm without a welded diff usually the right front tire spins. If you don't have a welded diff there is no way your car is still driving around with no power to the rear wheels. The vc would be burned up by now, and the car would barely move in gear.

Well you say that, but it drives just fine, spins the shit out of the front tires, especially the left one oddly enough. It shifts like butter in all gears. Believe me it's the weirdest thing I've ever seen.

I called Jack's, and unfortunately they don't have the same sales guy, it was some lady that didn't know what I was talking about and just told me to email the sales team.

 

[donniekak]

Usually this is how it happens. When you launch, the car squats and transfers weight to the rear. This gives the rear tires more traction, this also gives the front tires much less traction. The vcu is a pretty weak LSD, and is overpowered, allowing the front to spin, and minimal power transfer to the rear. I bet if you did a burnout in gravel all 4 tires would spin at first.

Although, you may have a bad viscous coupling exacerbating the situation.

 

[Turboturd]

Although, you may have a bad viscous coupling exacerbating the situation.

This is what I wanted to know from the beginning.

UPDATE:
With the TC off and the car in gear the output shaft of the trans turns normally.

The TC off the car turns perfectly with ease on its own. Even took the side cover off and inspected the bearings and teeth on the gear, everything looks good, almost no wear at all.

Put the TC back on the car, left the driveshaft off, and the output of the TC does NOT turn!

I'm very confused, but looking more like it's the viscous coupler to me.

I also found out that despite the fact that both of my TC's are 90 models with the iron front housing, they have different spline counts, one is a 22 and one is a 23. That and the other TC is frozen, it won't spin (probably because it sat for 5-10 years)

 

[pauleyman]

if one is 23 it isn't original to a 90 car

 

[Turboturd]

if one is 23 it isn't original to a 90 car

Yeah I know, you sold me the extra TC I have paul! Any ideas on my problem?

 

[bastarddsm]

grab the output shaft of the trans and see if it spins independantly of the front tires. (It shouldn't)

 

[4g63t]

This is what I wanted to know from the beginning.

UPDATE:
With the TC off and the car in gear the output shaft of the trans turns normally.

The TC off the car turns perfectly with ease on its own. Even took the side cover off and inspected the bearings and teeth on the gear, everything looks good, almost no wear at all.

Put the TC back on the car, left the driveshaft off, and the output of the TC does NOT turn!

I'm very confused, but looking more like it's the viscous coupler to me.

I also found out that despite the fact that both of my TC's are 90 models with the iron front housing, they have different spline counts, one is a 22 and one is a 23. That and the other TC is frozen, it won't spin (probably because it sat for 5-10 years)

When you say turns normally do you me by hand, or with the car on jack stands idling in gear?

 

[donniekak]

Do you have a 23 spline t case on a 22 spline shaft? Also 1990 t cases have an aluminum front housing for the most part.

 

[pauleyman]

? Also 1990 t cases have an aluminum front housing for the most part./QUOTE]
This is not true. If its original yes but the replacements or a recall unit are cast iron.

You couldve pulled the center diff by now. Something is broken in the viscous, ctr diff or output shaft. Remove and inspect.

 

[donniekak]

? Also 1990 t cases have an aluminum front housing for the most part./QUOTE]
This is not true. If its original yes but the replacements or a recall unit are cast iron.

You couldve pulled the center diff by now. Something is broken in the viscous, ctr diff or output shaft. Remove and inspect.

For the most part is correct. Most 1990 dsms aren't driving around on factory replacement cases.

 

[Turboturd]

Do you have a 23 spline t case on a 22 spline shaft? Also 1990 t cases have an aluminum front housing for the most part.

No, the shaft and TC currently on the car are 23 spline. So it must have been swapped by a previous owner at some point.

Thanks for all your replies, I will be taking the end cases off both my transmissions and checking the viscous couplers friday or saturday, I'm too busy to get it done before then. I will update you then

 

[Turboturd]

So I removed the VC's from both transmissions, tried to test them by securing the inner sleeve to a vice and twisting the outer by hand. Neither would spin. I found a thick grey fluid on the inside of the end case around the VC that has fine metal particulate in it. It is much thicker than the pink redline fluid that I had in the trans. I also removed the output shaft from the trans to get a good look at it and found it had serious wear to the splines. Same thing on the TC input shaft.
Here are some photos, let me know what to try next or what you think is going on

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Bottom shaft is the one that was on the car, top is from spare trans

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[pauleyman]

The problem seems pretty obvious to me. Stripped tcase splines will act just like no tcase. Replace the shaft, tcase (or its input) and the VC. Grease the shaft splines.

 

[donniekak]

Looking at that shaft, there is no way it came out of a jacks transmission.

 

[Turboturd]

Looking at that shaft, there is no way it came out of a jacks transmission.

I didn't send the trans to them, just bought a rebuild kit, and had them upgrade 1st and 2nd gear

I had a friend rebuild the trans, and we didn't even look at the center diff or the output shaft. The output shaft looked fine until I actually cleaned all the rust and grease off, I would never have noticed if I didn't remove it entirely from the trans

The problem seems pretty obvious to me. Stripped tcase splines will act just like no tcase. Replace the shaft, tcase (or its input) and the VC. Grease the shaft splines.

Finding a verified working VC ins't exactly easy. I can replace the shaft with the other one shown in the pic, or I have to swap the 22 spline shaft and TC input I got from you. The TC itself is frozen up from sitting or I would swap the whole thing. The TC gears and teeth are so large I don't see a problem with swapping just the input shaft, I wouldn't expect any abnormal wear, but I could be wrong

 

[pauleyman]

If you do ove that thing at all id pull the diff also and look inside. It shouldnt have driven anywhere. Suggests to me it may be broken as well.

 

[Turboturd]

I changed out the output shaft, put out back together and started it up on jack stands and all 4 wheels turn normally. Before I can even back the car out of the garage it starts spewing white smoke out of the engine bay and exhaust, so I somehow blew the turbo or the HG without leaving the garage. Just my luck with this car

 

[bonecollector]

I changed out the output shaft, put out back together and started it up on jack stands and all 4 wheels turn normally. Before I can even back the car out of the garage it starts spewing white smoke out of the engine bay and exhaust, so I somehow blew the turbo or the HG without leaving the garage. Just my luck with this car

By chance did you happen to have your down pipe off and happen to spill some sort of fluid down it?

When i installed my FMIC i looped the power steering lines and happen'd to spill a good amount of power steering fluid into the down pipe. As soon as i started it the garage and half the block was smoked out.

First thought was head gasket or turbo. I just about sh!t myself, eventually the smoke cleared.

 

[Turboturd]

If you do ove that thing at all id pull the diff also and look inside. It shouldnt have driven anywhere. Suggests to me it may be broken as well.

So I didn't take your advice initially, and didn't pull the center diff because I don't have the tools to take everything apart properly. But ultimately, I got it back in to a friends shop and he found the diff destroyed. Still have no idea how it was driving around FWD with no problem, because I swapped the VC and it would drag badly.
Real problem is that I don't have another 90 center diff! I do however have a 92 model from a spare trans that i will trade if anyone can help me out