[MikePL]

What pushed me to do the viscous coupler removal?

First of all when I made turns, for example, in a parking lot, I heard my tires scrub against concrete and one of the wheel stopped turning intermittently to relieve the stress on the drivetrain. Please note that my tires weren't squeaking but really dragging to the point that the truck would not roll while making a turn. Instead, it behaved as if the parking brake were applied. If your tires just squeal, especially on the slick kind of concrete found in shopping malls, then the VC (viscous coupler) is not your problem. Another way to find out if your VC is dead is to raise one wheel (tranny in N, transfer case in N). In the N/N position the wheel should move rather freely when you rotate it by hand. If you lock the center differential the wheel should not move (it might have play but you definitely can't make turns).

What can be the cause of the VC seizing?

The most often mentioned cause is running tires of different sizes. This causes the VC to operate all the time, heat up and seize permanently. I will not discuss the principles of the VC as this can be found in other threads and has already been explained extensively. In other words, the PO of my truck must have been a dummy and killed even such a friendly and simple device as the VC.

What can a seized VC damage?

First of all, a seized VC acts as a permanently locked differential. So when you drive in a straight line nothing happens but once you turn, even a little bit, the differences in tire rotation are not absorbed by the center diff but transferred onto all the drivetrain components. This puts enormous stress on your axles, driveshafts and all differentials. This, in turn, speeds up wear and sometimes may even break an axle or grind teeth in a diff. Such damage will surely cost you lots of time and $$$.

What does the VC give me?

It acts as a 'semi-locked' center differential. It means that if one axle loses grip, the engine torque is gradually transferred onto the other one. This is good not only for off road but also icy, snowy or wet roads. It's a kind of primitive traction control. Maybe 'primitive' is a bad word, as the VC is quite piece of engineering and craftsmanship, very simple but quite effective.

What will I get when I remove the VC?

I will simply get an open center differential. One can drive without the VC indefinitely and this will do no harm to absolutely anything.


PREPARATION FOR THE OPERATION.

You will need...
--- a garage where you have easy access under the truck.
--- 4 or 5 hours (if you do it alone)
--- a set of professional wrenches (very important, read further about it)
--- a 2ft steel tube to give leverage to your wrenches
--- a penetrating oil spray to loosen stubborn rusted nuts
--- gear oil if you don't plan to use the old one
--- RTV silicone or any kind of gasket material
--- a hard nylon sponge from your kitchen.
--- a file
--- a thread locker or at least dense paint if you want to lock the threads the redneck way (like me)
--- at least 4 kinds of snap ring pliers, you never know which will work for you
--- at least three flat screwdrivers of different sizes, including one which is very wide and hard
--- lots of paper towels or simply toilet paper
--- a camera or paper and pencil
--- a big syringe or pump to fill the differential with oil
--- patience
--- anything else that you will find necessary


1. Start with disconnecting the rear driveshaft. It is held by four screws, which you have to spray a bit to reduce friction and facilitate unscrewing. This is absolutely the point where you need the best quality wrenches. These nuts transfer big forces so they are really tight. The size of the nut is 14mm (as far as I remember) and you will probably have to use the steel tube for leverage. Chock the wheels to prevent the truck from moving. In my case, the small 14mm wrench had to withstand a 2ft leverage and a 160lb guy hanging on the end of it with full weight. A cheap wrench will snap right away causing danger or will deform itself and round the nut edges (say bye bye to driveshaft removal). So remember to use good stuff here.

2. Once the nuts are off you can pull the driveshaft away from the transfer case flange. If you have greased the shaft regularly it will probably be full of grease and won't retract. It this case you will have to remove the grease port on the shaft and use a big screwdriver to separate it from the flange. Use a file to scratch the flange and shaft joint to make sure you put it back in exactly the same orientation. Use a cord or wire to attach the shaft to the frame or exhaust tube, so that it doesn't hang around and make your work difficult.

Photo of rear of transfer case with driveshaft removed and attached to muffler.

3. Disconnect anything that connects to the back of the T-case. These will be...
a) speedometer cable which is in the middle of the photo below. This is a socket, so don't try to rotate anything, just lower the rubber boot, press the tab and pull.
b) grounding cable, seen below speedometer cable and a bit to the left.
c) two electrical plugs on top of back of T-case, not seen on the photos but easy to find. Mine snapped off with ease (remember to press the locking tabs) and probably yours will also be easy.
d) there might be some other stuff connected by previous owners so inspect the back of the transfer case.


Here you can see speedo cable, ground cable, drain plug on bottom, fill plug on upper left.

4. Drain the T-case. On the very bottom there is a plug (24mm). Put a socket wrench and loosen it. Loosen it further by hand. Negative pressure will prevent ani oil from leaking, so hold the plug firmly. When the thread ends it will pop off, and together with it a stream of oil, so have a container ready. Make sure the container is near to the opening as the oil is dense and it could drag itself in different directions. It will drain like this for at least 10 minutes and some dripping will continue for the next 4 hours (it means it's going to spill oil until you close the T-case again). Let it drain and have a break, dring a juice and eat a sandwich.

5. Loosen and remove the bolts that surround the T-case. You will have 9 bolts of different sizes, so remember to put them on the floor in order and take a note of them or take a picture like I did. This is to ensure that if you accidentally move the bolts around, you will be able to retrieve their original position.

Photo of bolts in the right order.

6. Now you have to separate the back of the T-case from the rest. You can use some sophisticated pullers and try to separate it, but you can also go the 'brute-dummy' way and simply point a flat screwdriver to the edge and bang it with a hammer. You will end up with a few dents on the mating surfaces, but you can tap them back to flatness with a hammer. Wiggle the screwdriver around to make sure you gave a gap everywhere. Remember to do it alternatively on both sides (left-right-left-right...) of the case. At this point you should be careful as the oil pump inside the case has a round metal spacer which might fall off. Do not lose it. Mine stayed sticked to the transfer case all the time but yours could fall, so be careful. See photo.


Left upper side shows the pump with the metal ring sticked to it in my case. In your case it could be on the other half of the pump or even on the floor, so be careful.

7. The photo below will show the back of the T-case. The big brown disc inside is the VC. Be careful while pulling the back of the case, as it is quite heavy due to the VC. The other half of the pump (with rotor) is also visible.



8. Now comes the most frustrating part !!! There is a C-clip that holds the VC on the shaft. Too bad the clip is surrounded by the VC flange, too bad the clip is quite hard, too bad the clip has no holes like most C-clips, too bad you have to remove it. You will be my guru if you do it in 20 minutes. I bet it will take you longer. I had to bend mine pretty badly to remove it, see below.


So once you remove the C-clip you can slide the VC off with ease. Damn heavy...

9. Make sure you wipe the mating surfaces with a paper towel. Use a nylon sponge (the hard type) to remove any gasket residue on the mating surfaces.

10. Apply gasket material (RTV silicone or similar) to one of the surfaces. Make sure to make a continuous path of silicone. Do not surround the bolts but make it on the inner side of the bolt holes, you don't want oil to leak through the bolt holes.

11. Put the case back on and tighten the bolts with little force. Before that make sure you align the pump rotor (tab) with the groove on the other half of the T-case. After a while tighten the bolts with proper force. Do not tighten them one by one in series but tighten them across the case to avoid any stress. Do not use too much brute force. Remember that you are working on aluminum and you don't want to snap any threads.

12. Put back all the electrical connectors.

13. Put back the driveshaft.

14. Use thread locker (Loctite or similar) on the driveshaft screws and nuts. I had no Loctite ('ve lost it somewhere) so I soaked the threads in paint. A worse solution (redneck-like) but better than nothing.

15. Plug the bottom of the T-case

16. Unplug the filler hole.

17. Fill with gear oil. You will have to use your intelligence here, as it is not so easy to fit a bottle over that hole. Use a special syringe or some other method. Feel free to experiment.

Inspect everything to make sure you have not missed any screws.

Enjoy.

I hope you enjoyed the tutorial.

Feel free to ask any questions.

Mike

[Hayes]

Awesome writeup and photos.

I hope this doesn't ruin your day, but you can get that c-clip of in 10 seconds with the right set of snap-ring pliers.

GuruHayes

[nakman]

cool. great writeup, thanks! do you know the torque specs for the case? DS is 55 ft-pounds, iirc. Great FAQ material for sure. :beer2:

[eldgenb]

when this is done, does the center diff lock still work if you have the swithch and pin 7 mod? Did you replace the VC with a part time kit or did you just remove it all together?

[CJF]

Eldgenb,

Don't confuse the Viscous Coupler with the Center Differential. He simply removed the VC, which, for example, 91-92's never had in the first place. (Other than that the transfer cases are supposedly identical.) He still has AWD, the center diff, and the ability to lock it. Anything like the "7-pin mod" or whatever it is (sorry, that doesn't apply to us 91-92'ers) should work exactly as before. In fact (and I might catch crap for saying this, but...) I doubt most 93-97 folks would even notice if their VC went AWOL (not seized, just removed) other than a little more driveline clunkiness.

Curtis
91FJ80

P.S. Got any more pic's of the pup in your avatar? My wife finds him irresistable.

[Cruiserdrew]

Originally Posted by Hayes

I hope this doesn't ruin your day, but you can get that c-clip of in 10 seconds with the right set of snap-ring pliers.

GuruHayes

Yep-I filed down a set of snap ring pliers to get the c-clip out undamaged. Took about 3 minutes with a file.

I've sort of forgotten how the torque flows, but if you took the VC out, do you still have drive to the rear output shaft?

Just me, but I would have bought a new one, or called Slee for the part time conversion kit.

Just curious-the inside of your case looks really dirty. What is the service history? Normally, the metal surfaces are clean, and brighter.

[CJF]

Originally Posted by Cruiserdrew

Just me, but I would have bought a new one, or called Slee for the part time conversion kit.

I don't get this. You're acting like he pulled out the whole guts of the transfer case. Christo himself has conjectured that the VC was added primarily to control driveline slop and the infamous 91-92 clunkiness. The VC is NOT the center diff, which he still has.

Did you read my post just above yours?

Sorry for getting defensive,

Curtis
91FJ80, same TC as you but no VC.

[eldgenb]

P.S. Got any more pic's of the pup in your avatar? My wife finds him irresistable. [/quote]

PM me your e-mail and I will send you some pics of her.(the pup)

[Doc]

That was a very nice write up, but how does it drive now? I'm assuming it solved your biding issues?

[Cruiserdrew]

Originally Posted by CJF

I don't get this. You're acting like he pulled out the whole guts of the transfer case. Christo himself has conjectured that the VC was added primarily to control driveline slop and the infamous 91-92 clunkiness. The VC is NOT the center diff, which he still has.

Did you read my post just above yours?

Sorry for getting defensive,

Curtis
91FJ80, same TC as you but no VC.

Defensive?-it's just the internet. I've had this apart awhile ago, and what I remember is that the rear output shaft is coupled to the rest of the t-case by the VC. I totally understand that the center diff is still there.

It's been awhile, but there are 2 sets of splines on the VC, and the torque is coupled one way when open and another when the center diff is locked. What I am trying to impagine is how it is coupled at all with the VC out. I'll have to pay closer attention next time I'm in there to replace the output seal. It is not an intuative device like most things with gears and bearings.

If you have pics of the tail section of the 91 transfer case open, I would like to see them for comparison. I thought the VC was added due to the pecularities of the ABS system and to bias some torque to each axle in the setting of one axle wheel spin. I have never heard that it was added to control clunkiness. Maybe, though! It is an odd and poorly understood device in this application, at least by me.

[e9999]

and -as usual- always remove the filler plug first, *before* the drain plug!

[alia176]

So, now what happens? Is he now a part time 4x4? He is no longer full time 4x4, that's for sure. I assume that once the front or the rear wheels lose traction, they'll continue to do so until the CDL is activated. Yes?

[RavenTai]

Originally Posted by Cruiserdrew

Defensive?-it's just the internet. I've had this apart awhile ago, and what I remember is that the rear output shaft is coupled to the rest of the t-case by the VC. I totally understand that the center diff is still there.

It's been awhile, but there are 2 sets of splines on the VC, and the torque is coupled one way when open and another when the center diff is locked. What I am trying to impagine is how it is coupled at all with the VC out. I'll have to pay closer attention next time I'm in there to replace the output seal. It is not an intuative device like most things with gears and bearings.

If you have pics of the tail section of the 91 transfer case open, I would like to see them for comparison. I thought the VC was added due to the pecularities of the ABS system and to bias some torque to each axle in the setting of one axle wheel spin. I have never heard that it was added to control clunkiness. Maybe, though! It is an odd and poorly understood device in this application, at least by me.

This seams to come up over and over again, people have the impression that the VC is a transmitter of drive torque to the rear axle, the 80 is not like an AWD Audi or Subaru or LR where thre is no direct connection to one axle, in our case the VC is used differently it is a limited slip device that dampens the center differential. the rear drive runs right through the center of the VC from the center diff to the rear output flange uninterrupted, the VC is splined to that shaft and to the center diff carrier, since for the center diff to differentiate between the front and rear outputs the rear shaft and the diff carrier have to spin at different speeds, the VC splined to both will resist this differential rotation.

now with the VC removed it is still full time 4 wheel drive, both axles are sill driven like before but the center diff is no longer limited slip, if one axle or the other gets on ice for example that axle can receive all the drive RPM (can be either front or rear) , exactly the same as the 91/92 FJ80, same as a open unlocked diff in an axle, the CDL will still work and when needed can be locked to keep the front and rear drive shafts locked to each other rotating at the same RPM like a part time T-case.


http://webpages.charter.net/raventai...20TRANSFER.pdf

[-Spike-]

Yes, he's still full time 4wd. Just like having one drive axle with an open diff is 2wd. He has two driven axles, and no way to disconnect either one. He simply has an open diff in the t-case now, instead of a semi-open diff in the t-case.

-Spike

[RavenTai]

this is likely the clearest picture from that PDF hopefully that will help.

[Hayes]

Yes.

Pretty cool setup, I think.

Originally Posted by RavenTai

This seams to come up over and over again, people have the impression that the VC is a transmitter of drive torque to the rear axle, the 80 is not like an AWD Audi or Subaru or LR where thre is no direct connection to one axle, in our case the VC is used differently it is a limited slip device that dampens the center differential. the rear drive runs right through the center of the VC from the center diff to the rear output flange uninterrupted, the VC is splined to that shaft and to the center diff carrier, since for the center diff to differentiate between the front and rear outputs the rear shaft and the diff carrier have to spin at different speeds, the VC splined to both will resist this differential rotation.

now with the VC removed it is still full time 4 wheel drive, both axles are sill driven like before but the center diff is no longer limited slip, if one axle or the other gets on ice for example that axle can receive all the drive RPM (can be either front or rear) , exactly the same as the 91/92 FJ80, same as a open unlocked diff in an axle, the CDL will still work and when needed can be locked to keep the front and rear drive shafts locked to each other rotating at the same RPM like a part time T-case.


http://webpages.charter.net/raventai...20TRANSFER.pdf

[CJF]

Originally Posted by Cruiserdrew

Defensive?-it's just the internet. I've had this apart awhile ago, and what I remember is that the rear output shaft is coupled to the rest of the t-case by the VC. I totally understand that the center diff is still there.

It's been awhile, but there are 2 sets of splines on the VC, and the torque is coupled one way when open and another when the center diff is locked. What I am trying to impagine is how it is coupled at all with the VC out. I'll have to pay closer attention next time I'm in there to replace the output seal. It is not an intuative device like most things with gears and bearings.

If you have pics of the tail section of the 91 transfer case open, I would like to see them for comparison. I thought the VC was added due to the pecularities of the ABS system and to bias some torque to each axle in the setting of one axle wheel spin. I have never heard that it was added to control clunkiness. Maybe, though! It is an odd and poorly understood device in this application, at least by me.

Ah, I see what you're asking now. Hopefully I didn't get this thread too off track for Mike to respond. Edit: Good ol' Raven's got it covered.

I agree with everything in your last paragraph. But that is a quote from Slee; I'll see if I can dig up the thread.

Edit: Here it is.

http://forum.ih8mud.com/showpost.php...8&postcount=33

Good thread, with an inflammatory post by yours truly on page 1.

Cheers,

Curtis

[Hayes]

That picture shows it well.

Sometimes I find the system hard to visualize. The key is realizing that the VC is connected to the shaft and to the carrier, and the output shaft is splined to the side gears of the diff.
It helps me to think of the shaft being driven by the side gears, and the VC driven by the carrier--when the side gears and carrier are rotating at different rates, the VC applies the brakes (transfers torque) to the shaft/carrier.
Kind over simplified, but it all works out in my head...

[RavenTai]

Originally Posted by Hayes

Yes.

Pretty cool setup, I think.

agreed a "viscous coupling type Limited Slip Differential" is much better than a "Viscous Coupling center differential"

[MikePL]

OK, so now the truck drives like a marvel. I can turn the wheels to the max and drive in circles all day- no squealing, no rubbing, no tension. The truck rolls pretty easily. I do have a bit of clunking in the driveline but it only happens when shifting from R to D and vice versa. During normal driving and shifting gears there are no sounds. This is probably because the PO has been driving the seized VC for over a year and the differentials must have developed play.

My plans for the future are a new (or used but working) VC because I would like extra traction in winter without locking the center diff. Unless it doesn't lock fast. Here is a question for the guys with working VCs. Does the VC act really fast when one wheel loses traction? Does it act after a full turn of the wheel or maybe require more time?

To sum it all up:
I am happy with the VC removal.
The truck is still full time 4WD
The task was relatively non-complicated

[RavenTai]

the VC does not react in so many revolutions, it is more sensitive to rate, if a tire was slipping slowly it would not do anything ever, not sure about the "Humping" (locking phase) but the resistance phase is instantaneous and strong and gets stronger with more RPM difference

[Rusty Phillips]

Im wondering if you can dissassemble the VC and change / refill the fluid (silicone?) inside it?

kind of like Toys R us was doing with fan clutches

more pics of the removed VC please.....

[MikePL]

Do you think oil is the culprit? The VC is seized. The seizing is caused by overheating, so I suppose some elements are bent, melted or broken. But if it is just a question of oil, then I can disassemble it and have a look. I've nothing to loose anyway.

[Walking Eagle]

Originally Posted by Hayes

Awesome writeup and photos.

I hope this doesn't ruin your day, but you can get that c-clip of in 10 seconds with the right set of snap-ring pliers.

GuruHayes

yep - from the t-case bearing thread

You'll need a Craftsman Lock Ring Pliers (Sears item #00947386000 Mfr. model #47386)

http://forum.ih8mud.com/showpost.php...81&postcount=6

might be a better one out there but this one works, though it is tight. I was probably somewhere between 10 seconds and 20 min.

[Walking Eagle]

Originally Posted by MikePL

6. Now you have to separate the back of the T-case from the rest. You can use some sophisticated pullers and try to separate it, but you can also go the 'brute-dummy' way and simply point a flat screwdriver to the edge and bang it with a hammer. You will end up with a few dents on the mating surfaces, but you can tap them back to flatness with a hammer. Wiggle the screwdriver around to make sure you gave a gap everywhere. Remember to do it alternatively on both sides (left-right-left-right...) of the case.

There is also an 'ear' on the housing, that you can just use a pry bar on on the drivers side, the passenger side there is a point that you can hit with a drift punch. I tried the rubber mallet mehod, that didn't work worth a crap, then I made a little stap holder to mount into one of the threaded holes on the housing and hooked a strap to the frame to try to pull. Nothing. Pry bar on the tab is waht finally did it for me.

here's where Hayes talkes about using a drift punch

http://forum.ih8mud.com/showthread.p...ht=output+seal

borrowed this picture from that thread - the red arrow I added is the tab / 'ear'. I think anyway...

[alia176]

Originally Posted by Walking Eagle

yep - from the t-case bearing thread

You'll need a Craftsman Lock Ring Pliers (Sears item #00947386000 Mfr. model #47386)

http://forum.ih8mud.com/showpost.php...81&postcount=6

might be a better one out there but this one works, though it is tight. I was probably somewhere between 10 seconds and 20 min.

There may not be a Sears in Warsaw, Poland

[MikePL]

I've bought a set of professional lock ring pliers a few hours after the task. I had four kind of such pliers but none of them worked for the tight place where the ring is. Yes, I know I could have written 'get SST no.XXXX and the ring will pop off', but I wanted to do the task with the simplest set of tools possible, to encourage people that such things can be done without a complete car workshop.

[UpsideDown]

I just completed this surgery on IronYuppy's 80 series at my shop this afternoon.

It's a very simple job, and in total the VC removal probaly took about an hour and a half to two hours with a few interruptions from the phone, my apprentice, and ensuring that everything was cleaned and inspected before reassembly.

I can't think of anything that would complicate the Re & Re other than forgetting to install the oil pump drive or something similar. In doing a final inspection of things, I have also decided to replace the rear u-joints as they are not totally smooth anymore (original units still in place).

Anyhow, thanks for the write up and photos. I could post photos as well, but they'd look almost exactly the same.


John

[Romer]

Did this fix Ironpuppy's binding issue? If so, pictures of the coupler with a guess what caused it would be useful in this thread.

[concretejungle]

Originally Posted by Romer

Did this fix Ironpuppy's binding issue? If so, pictures of the coupler with a guess what caused it would be useful in this thread.

yes, please do tell. I have a terrible suspision that i may be having some of the same issues.

When i turn sharp in a parking lot, i feel an almost wiggle as if a wheel is loose, or an inner wheel is binding.