Rebuilt transfer case options with viscous coupling discussion.

[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)