Rebuilt transfer case options with viscous coupling discussion.

[eaglefreek]

Due to another thread regarding viscous coupling availability,  I made a couple phone calls. Both were to companies who supply rebuilt transfer cases to Autozone. This was to see how they handle the viscous coupling issue. If others want to grab the torch and call other rebuilders and pick their brain and add that info here, it would be great.

First call went to Midwest Transmissions. After a getting transferred a few times and making a couple more calls to them, I finally received an answer. They say they have a supplier who rebuilds the VC's for them.

Second call went to Rockland Standard Gear. I called and had to leave a voice mail. I got a call back the next day. The gentleman was quite knowledgeable about the AMC Eagle. He said he had owned several over the years and his dream car was an AWD Pacer using Eagle drivetrain components. I felt bad misleading him into thinking I was looking to purchase a rebuilt transfer case. If he reads this I hope he understands. He first tried talking me into swapping to a different case. He said all his Eagles got a NP231 and he modified the linkage of the NP229 range lever to work with the 231. I told him I wanted to know what they do about the VC. He stated they haven't been available for 20 years and before going to work for RSG he had a tranfer case company where he was the only one in the country who rebuilt VC's. He developed an apparatus to test them. He says they have to be heated up by turning them and that you can think you have a bad VC but once the fluid is warmed up the VC will work properly. He had to abandon the VC rebuilding business because the the fluid was considered toxic and was getting alot of heat from the EPA. He stated that Rockland Standard Gear tests used couplers and reuses ones that pass their test and they do not rebuild the coupler or use rebuilt ones.

Please only add technical info to this thread.

[A-A EAGLE]

Thanks for the info, egg for you.

Although not very technical, I rebuilt my VC by bolting the friction plates that are inside the VC together. Not an option for full time 4x4 and those who don't want to loose the pro's of the working of the VC. But for those who use 4x4 only for off road and snow and ice conditions, its a solution which will cost 3.00 USD.... Beware, in this case you can't use 4x4 on normal road conditions as the transmission will wind up and will cause damage.

Anjo

[Jurjen]

Here are four videos of a VC rebuild (for a VW T3-synchro).
It is in German, but still self explanatory.
It also lists the sort of silicone oil used.

http://www.2wd-goes-syncro.de/

[rohnk]

Very cool Jurjen! Do they say why the reason for the rebuild?

[captspillane]

I would be excited if their testing procedure could give a tangible rating on a used coupler, like several torque factors in in-lbs or even just a performance rating from one to ten. Just knowing it still works doesn't pass judgement on how long it will continue to work. Mileage doesn't say much about a VC's status with some Eagles left in all wheel drive and others driven routinely in 2wd.

Specifically I wouldn't trust their testing procedure without a description of how they compensated for a lower initial viscosity. That would effect how long it would take for the fluid to reach operating temperature. Worn fluid may still reach a necessary torque value when actively spun, but would not be as responsive as new fluid. In normal operation the two differential outputs are usually married together without VC assistance, so it would not have the relative motion to build up heat with.

I'm imagining a device that clamps the housing still and measures the applied torque necessary to keep it still while the center turns a known RPM. I would expect an initial torque value for the fluid cold, a normalized torque value for the fluid after a standardized number of applied rotations, and a concluding torque value once the fluid reaches an optimal temperature. All three are necessary to quantify how worn a unit is and how responsive it will be relative to a new unit. 

I would love to be able to strip all my VCs out and send them to a testing location if I can get a formal report for each one that indicates exactly how worn it really is. The new old stock units are expensive enough to make that worthwhile.

[captspillane]

His statement that Viscous Couplings haven't been produced in 20 years is exaggerated by a few years. They were last installed by New Venture in a production Jeep in the 1998 NP249. The 247 took over in 1999 using a limited slip differential. The switch was performance driven and other makes still produce viscous couplers. 

Here are some quotes I found at this website regarding the 247 limited slip versus the 249s viscous coupling:

http://www.allpar.com/mopar/transmissions/NVG-history.html

"It's all in response time. The new unit essentially works in two-wheel drive until wheel-slippage is detected; then reaction time (to send drive to the other axle) is about 40 milliseconds. A viscous coupling can take two or three seconds to do the same thing."  It also “integrates seamlessly with antilock braking; viscous-coupled diffs have to allow 'freewheeling' under braking to avoid potential conflict between trying to drive all four wheels and trying to brake wheels that may be working with difference coefficients of friction. ... the interplay between the geroter pump and the progression of clutch lockup allows the unit to more easily tailor performance characteristics to a wide range of applications.”

[eaglefreek]

I have no idea the procedures they use. I don't know if it's scientific or a a drill and a vice is used. I don't think it has been confirmed the 249 VC is the same as the Eagle's VC and that is the one he was referring to when saying they weren't produced for 20 years. He seemed to be a really friendly guy. Unfortunately I was driving when he called and didn't catch his name. If you call RSG  and tell them you have a technical question regarding transfer cases you will get transfered to him.

[Jurjen]

Here  i found some interesting torque curves for the VC.
Note that this curve is for the VW synchro again, but this website has lots of interesting information.

http://www.syncronauts.org.uk/syncro-technical/syncro-transmission/viscous-couplings/refurb-vcs-torque-curves

Use the tab "synchro technical" to find out more.

[Jurjen]

I also found some information from GKN:
http://shufti.files.wordpress.com/2010/04/viscous-engl.pdf

GKN is the company in the UK that Roy Lunn approached for the viscous biasing differential.
The viscous unit was developed by FF Devolpments Ltd in Coventry UK, but they had sold the manufacturing rights to GKN.

For production Roy Lunn used  a 15,000 centistoke silicone oil at a fill rate of 70%.
I guess that Roy Lunn wanted to prevent the Eagle going in "Hump" mode (viscous  coupling lock-up) to compensate for normal variation of the rolling radiuses between front and rear tires.

I sometimes wonder, if broken half shafts are the result of a locked up viscous coupler?
The VW guys say that the "Hump" can be recognized on a dry pavement going through a corner feels like it doesn't want to go and one of the tires will be slipping.

[68AMXGOPAC]

I also found some information from GKN:
http://shufti.files.wordpress.com/2010/04/viscous-engl.pdf

GKN is the company in the UK that Roy Lunn approached for the viscous biasing differential.
The viscous unit was developed by FF Devolpments Ltd in Coventry UK, but they had sold the manufacturing rights to GKN.

For production Roy Lunn used  a 15,000 centistoke silicone oil at a fill rate of 70%.
I guess that Roy Lunn wanted to prevent the Eagle going in "Hump" mode (viscous  coupling lock-up) to compensate for normal variation of the rolling radiuses between front and rear tires.

I sometimes wonder, if broken half shafts are the result of a locked up viscous coupler?
The VW guys say that the "Hump" can be recognized on a dry pavement going through a corner feels like it doesn't want to go and one of the tires will be slipping.

I have felt the hump on the VW setup.Have a 91 ( ermmm oh yeah it says a 72 ) here in states to make it legal,lol. It is a Transporter with the 4wd synchro, sold a convereted to synchro Vanagon a couple years ago.Both are great vehicles, never knew the AMC and VW had something in common.

[carnuck]

Did you know the 2.0L in Gremlins and '79/80 Postal Jeeps was Audi/VW? SX-4 would have had the 2.0L if it wasn't for the complaints of Grem owners due to it being "gutless", yet Porsche liked the motor enough to stick it in their 924s and some got turbos!

[68AMXGOPAC]

Now that's interesting, so find an old postal jeep, pull the engine and add a Porsche turbo !! Sweet.

[eaglefreek]

Getting a little sidetracked, let's stay on the original subject. Thanks

[Draekon]

So when in comes to rebuilding the viscous coupling, does anyone know how much fluid is supposed to go in it?

I assume the seals and such are out there, although it may take quite of bit of work measuring, and tracking them down.

[Hawk258]

I believe the Eaglepaedia has something in there about fluid levels and volumes. But you could google NP128/np129 for that info. But someone here may know as well, I will update this if I find it first.

ok here is the link for the TM, scroll down to the NP 128 is says 3.3 liters (7 pints)

http://www.amceaglenest.com/~iowaeagl/guide/index.php?title=July_1985_-_IS_7E_-_General_Information_and_TSM_Pages_for_the_NP_128_Transfer_Case

[mudkicker715]

I believe the Eaglepaedia has something in there about fluid levels and volumes. But you could google NP128/np129 for that info. But someone here may know as well, I will update this if I find it first.

ok here is the link for the TM, scroll down to the NP 128 is says 3.3 liters (7 pints)

http://www.amceaglenest.com/~iowaeagl/guide/index.php?title=July_1985_-_IS_7E_-_General_Information_and_TSM_Pages_for_the_NP_128_Transfer_Case

That would be magic for a vc to hold that much

[captspillane]

The service manuals don't detail how to rebuild a viscous coupler. Its supposed to be done in a factory. The 3.3 L capacity is for the whole transfer case.

Why bother looking for that amount until we have a source for the silicone fluid? Its special stuff and some degree of toxic. Is there a place to order the Viscous Coupler fluid for a VW or other make?

[Hawk258]

**Shrug** that's what the book said. it called for dex II and 3.3 liters. check the link I assume that would be from completely empty though.

[Hawk258]

Sorry... the 128 does NOT have a VC... it was a bad example I pulled the wrong case info... sorry.

[mudkicker715]

Sounds right for the case. However some cases use other lube such as 10w30

[Hawk258]

ok here is an update and an image of a VC, this may help and it appears that it is possible to get the VC fluid. I assume that it is possible to order the clutches for the vc not sure still flexing my google fu here.

http://www.vanagon.com/syncros/technica/vc-expert-interview/index.htm

[captspillane]

So when in comes to rebuilding the viscous coupling, does anyone know how much fluid is supposed to go in it?

Its the right answer for the wrong question. The question asked was how much viscous silicone oil is contained in the viscous coupler. It should be less than a pint. Its possible that the fluid from a VW viscous coupler is still in production and available to allow someone to rebuild their own viscous coupler. Its the fluid that loses its viscosity over time, the internal parts themselves are not in contact and should not wear out.

To be clear, the viscous coupler is about 4 inches in diameter and about  4 inches long. It is one internal part inside the transfer case.

[Hawk258]

well, It I think the answer is in my previous post, as there is suppose to be room for expansion. but that's just what I understand at the moment

[eaglefreek]

What I have read there needs to be the right combo of oil and air for it to work properly. The gentleman I talked to at RSG said he used to get 5 gal buckets of the oil from Dupont. No idea what it is or if it is still available.

[Hawk258]

What I have read there needs to be the right combo of oil and air for it to work properly. The gentleman I talked to at RSG said he used to get 5 gal buckets of the oil from Dupont. No idea what it is or if it is still available.

yes I have found some from the manufacturer but they link you to a local distributer, I will post the like for you folks that are interested.

http://www.dowcorning.com/applications/search/products/details.aspx?prod=02967642&type=PROD

[carnuck]

I believe the Eaglepaedia has something in there about fluid levels and volumes. But you could google NP128/np129 for that info. But someone here may know as well, I will update this if I find it first.

ok here is the link for the TM, scroll down to the NP 128 is says 3.3 liters (7 pints)

http://www.amceaglenest.com/~iowaeagl/guide/index.php?title=July_1985_-_IS_7E_-_General_Information_and_TSM_Pages_for_the_NP_128_Transfer_Case

Except the NP128 has no viscous coupler. That's the tcase lube oil they are talking about it.

[carnuck]

So when in comes to rebuilding the viscous coupling, does anyone know how much fluid is supposed to go in it?

Its the right answer for the wrong question. The question asked was how much viscous silicone oil is contained in the viscous coupler. It should be less than a pint. Its possible that the fluid from a VW viscous coupler is still in production and available to allow someone to rebuild their own viscous coupler. Its the fluid that loses its viscosity over time, the internal parts themselves are not in contact and should not wear out.

To be clear, the viscous coupler is about 4 inches in diameter and about  4 inches long. It is one internal part inside the transfer case.

In FSJs, the coupler tears apart and the silicone fluid eats up the bearings like liquid sand.

[Hawk258]

Sorry... the 128 does NOT have a VC... it was a bad example I pulled the wrong case info... sorry.

yeah, I updated that, again I apologize for that.

[Jurjen]

Here is the original GKN patent:

http://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=4022084A&KC=A&FT=D&date=19770510&DB=EPODOC&locale=nl_NL

It makes interesting reading.

The GKN people knew that it worked, but did not know why ....

The original silicone oil also came from Dow Corning ....

Some statements about filling in it too.
The coupler starts really doing something once 100% fill rate is reached due to thermal expansion. So fill it 100% and don't close it. Warm it up to 212F and the excess goop will flow out. Then close the coupler. Now you know that you have a coupler that starts working from 212F. Easy peasy.

Roy Lunn must have done the same experiments and came to a 70% fill rate.

I would do it like this:
Clean the internals with white spirit.
Then fill it to the brim with white spirit.
Empty it in a glass measuring cup (from the kitchen) and make a note of the level.
Use the same cup and fill it with silicone oil 70% of the previous measurement and put that in the viscous coupler.
Why not use the silicone oil to do the measurement? It is too goopy, it won't come out again.
So better use something nice and thin like white spirit.

[carnuck]

Found out the S10 axles are 5/16" longer fully compressed.

[captspillane]

I dismantled a 129, 242, and 249 transfer case today. The 129 viscous coupler had leaked all of its silicone fluid out. I was horrified to find that the viscous coupler has one puny O ring and a snap ring keeping it together. The 249 Viscous Coupler is drastically different. It is welded together and seems much more robust. I like that the 129 unit forms a donut around an open diffential, so once it fails that continues to let the transfer case have limited function. I don't like that its designed to fail easily and often.

I will be converting most of my Eagles to the 242, and a couple to the 249. I've already had a 242 in my Red SX4 for several years now.

I did find out that a viscous coupler could be added to the 242 at the sacrifice of the 2wd function. I have no need for 2wd in an Eagle, so this is something I would want to do. It would require the 249 output shaft to be grafted where the 242 output shaft was, so it would require a new shaft to be machined. Obviously this is cost prohibitive. It was cool to see tho that everything else would be an unmodified part from either a 242 or a 249. Actually the right splines are near the right place on the 242 shaft and the case itself is easily compatible.

[captspillane]

In FSJs, the coupler tears apart and the silicone fluid eats up the bearings like liquid sand.

The 229 and 129 are identical in the rear half of the transfer case, so I can now see how this could be true. The coupler doesn't tear apart, but the dinky little Oring lets all the silicone oil to leak out. I have trouble believing any 25 year old transfer case still has a working viscous coupler after seeing how one is constructed. The oil doesn't look abrasive to me, but it is very thick and I can see how it will clog and slow the proper oil from getting where it needs to go. I do not want any 129s or 229s in any of my Eagles.

I did figure out why the 229 is still a worthwhile transfer case to find. I want one for my XJ. The viscous coupler is easily drained and pins put in the plates to make a case with the same shift characteristics as a 231. It has a much wider chain than the 231 and also seems stronger. This would be alot cheaper than buying a slip yoke eliminator kit. 

Putting pins in a 129 would limit the car to 2wd except in slippery conditions, so I don't suggest using that method to retain one in your Eagle.

[Jurjen]

Good job Capt'n!
Liked the pictures in the other thread too.
I guess for "normal mortal" Eagle users it would be OK to change oil regularly and accept that the silicon oil slowly drains out?
It will still have the open diff function like the NP128 (1986 only).

[eaglefreek]

Yes, great info there. I have seen a couple pics of cracked VC's over at the FSJ site at one time. I put a 229 in my Eagle and bought another for spare parts and both VC's seem  to function correctly. I guess it's possible if the vehicle is rarely if ever put in 4wd, that it may extend the life of the VC.

[mechanic80]

Regarding the availability of viscous coupling fluid; I spoke with Dow Corning and the quart/pint/gallon/5 gallon sizes are indeed no longer available.  However, under a different number, I was told 55 gallon drums ARE available.  When I thought of the cost and freight charges added, I didn't pursue the matter, but maybe if enough people are interested, it could be economically possible. How many pints to a gallon?!  One downside would be shipping costs both to procure the drum and to the end user, but considering it's status as UNOBTAINIUM  this may be doable. What would spark interest is rebuilding instructions in english.  I'd like to see that! Any thoughts?

[carnuck]

In FSJs, the coupler tears apart and the silicone fluid eats up the bearings like liquid sand.

The 229 and 129 are identical in the rear half of the transfer case, so I can now see how this could be true. The coupler doesn't tear apart, but the dinky little Oring lets all the silicone oil to leak out. I have trouble believing any 25 year old transfer case still has a working viscous coupler after seeing how one is constructed. The oil doesn't look abrasive to me, but it is very thick and I can see how it will clog and slow the proper oil from getting where it needs to go. I do not want any 129s or 229s in any of my Eagles.

I did figure out why the 229 is still a worthwhile transfer case to find. I want one for my XJ. The viscous coupler is easily drained and pins put in the plates to make a case with the same shift characteristics as a 231. It has a much wider chain than the 231 and also seems stronger. This would be alot cheaper than buying a slip yoke eliminator kit.  

Putting pins in a 129 would limit the car to 2wd except in slippery conditions, so I don't suggest using that method to retain one in your Eagle.

If you want a case that's like the 231, but with a stronger chain and fixed yokes, an '80 up FSJ's NP208 is the ticket (just not from a V8 4 speed. They are 31 spline input with the Ford T18As, like the set I have for sale with a 360 from my '82 Honcho)