Where can I buy new viscous coupling for transfer case?

[priya]

It has been in a different spot several times for me.  Not that it matters too much for this since it doesn't find anything for a 129 coupler, but the address is google.com/prdhp .  That is the product search that the "shopping" selection brings you to.

Thanks Hokie Eagle, that took me there.  I put in 119 viscous coupler and it gave me 3 links for shopping, most of the links listed a wide array of products that had nothing to do with a transfer case and one link had one link that listed a 249 viscous coupler, but no 119.

[Hokie Eagle]

Glad that worked out.  I use the shopping on there quite a bit.  It is pretty useful most of the time.  Not that great with car parts though.

[Draekon]

An easier URL to remember for google shopping is simply shopping.google.com
Takes you to the same place.

[captspillane]

I got home today and went right to work dismantling a 129, a 242, a 231, and a 249 Transfer case. I learned alot in a short amount of time. The 249 viscous coupling is drastically different than the 129 viscous coupling. This first picture shows the 129 on the right and 249 closer to the left, the second shows the front of the 129, and the third shows the front of the 249

[captspillane]

The 129 is the same as the 229 from the chain back, because the low range planetaries in the 229 are all located deep into the case near the transmission. The 129 input shaft goes through a differential before getting to the output shaft. This diffential is in the center of the viscous coupling. The clutch plates and silicone oil actually form a donut around the differential. The outside of the donut is splined into the rear driveshaft and the center of the donut is splined to the front driveshaft through the chain. The inner and outer parts of the viscous coupling are held together by a big snap ring, which I opened to reveal the plates inside.

In contrast, the 249 Viscous coupler does not have a differential in the center. The unit is welded together and does not seperate like the 129 does. In the first picture you will see the three components that make up the 129 viscous coupler next to the single black object that is the 249 viscous coupler.

The 129 has the widest chain. 129 chain is 1 7/8" wide, 249 is 1 1/4" wide, and the 242 is only 1" wide. The second picture shows the internals of the 129.

[captspillane]

I also took apart a 242. I was rather impressed by it. Its alot more complex than the other two. It has an extra function than all the other Jeep transfer cases. It has both "4wd full time" and "4wd part time." This means that it can lock the two outputs together or leave them connected through an open differential. My dream transfer case would be a 242 with viscous coupling instead of an open differential in "4wd full time." I found that it is indeed possible to do, but it would require a custom output shaft. If I was willing to pay the machinist costs for that one part, all the rest would be factory parts from either a 242 or a 249.  There are the right splines near the right places already on the 242 shaft for the 249 viscous coupler, but putting it there would bridge the front and rear driveshaft yokes in both "2wd" mode as "4wd full time." It turns out then that the reason New Venture didn't put a viscous coupling in the 242 is that it would eliminate the 2wd function.

First picture shows the inside of a 242, the second shows the inside of the 249, and the third shows the 249 with its viscous coupler in place.

[captspillane]

The original question is about replacing 129 viscous couplers. I dislike them immensely now. When I opened this transfer case I found that all of the viscous silicone oil had leaked out of the coupler and filled up the case. This has the potential to damage the other parts of the case. I was surprised and even horrified to see how easily the viscous coupler came apart. It has one puny O ring underneath the snap ring with the task of keeping all the silicone fluid inside. The 249 unit in contrast is welded together and cannot be taken apart without destroying it.

Its my steadfast opinion now that the 129 should be replaced by a 249 or 242. The 249 viscous coupler is much more reliable and robust, although it does not have an open differential incorporated into it.

This picture shows a 129 the front driveshaft yoke of an Eagle next to the front yoke from the 242 and the 249. They're different but directly interchangeable.

[priya]

My head is spinning.  Captspillane earlier it was suggested the 119 and 229 VC's are the same, are they also the same as an NP249?  Can I get an NP249 VC and put it in my 119 transfer case with no modifications?  There are a number of NP249 VCs available on ebay for reasonable prices.

I am also confused by several people telling me I will still have power to both front and rear wheels if the viscous coupling is bad.  According to this description:

http://auto.howstuffworks.com/differential5.htm

of a VC posted on the nest the only thing connecting the front wheels to the rear wheels is the VC and to me that means of the VC is bad there can be no power to the front wheels.  How do the front wheels get power if the 119 VC is bad?

[BenM]

Do you know what year the 249 is? There were two distinct 249s, one that locked in low and another that didn't, and I've been wondering if the earlier one had an open differential. I do know some of the late 249s had "249OD" stamped on them.

It's also nice to see the 242 and 249 have fixed rear yokes. I believe the change was in 1995 to 1996.

[Draekon]

My head is spinning.  Captspillane earlier it was suggested the 119 and 229 VC's are the same, are they also the same as an NP249?  Can I get an NP249 VC and put it in my 119 transfer case with no modifications?  There are a number of NP249 VCs available on ebay for reasonable prices.

I am also confused by several people telling me I will still have power to both front and rear wheels if the viscous coupling is bad.  According to this description:

http://auto.howstuffworks.com/differential5.htm

of a VC posted on the nest the only thing connecting the front wheels to the rear wheels is the VC and to me that means of the VC is bad there can be no power to the front wheels.  How do the front wheels get power if the 119 VC is bad?

Based on the description that Captspillane gave, the 249 VC will not work in the 119.  Also, with the 119, the front and rear wheels are connected through an open diff, but if the speed difference is too great, the VC heats up locking the front and rear together instead.  In contrast, in the 249, there is no open differential connected to the VC, so if the VC goes bad in a 249, you will not have any power to the front wheels.

[priya]

Thanks Draekon, I understand that.  The viscous coupling is basically performing the same function as a clutch pack in a limited slip rear end differntial.

I'm still wondering about the 249 working in the 119 as Captspillane talked about it not being compatible with the 129 and never mentioned the 119.

[captspillane]

The first digit is supposed to mean 1 for single speed, and 2 for dual speed (meaning it has a low range). The second digit was supposed to mean the number of modes it had, but then it changed to mean the strength rating. The 231 for instance was intended for Jeeps, while the 242 was intended for militay Humvees and full size trucks.

A 119 became a 129 just by making slight changes to add a 2wd mode. The case and viscous coupler is identical. The 129 had a low range planetary added near the input shaft to become a 229. It also happens that the rear case extension is clocked differently, but all of the castings and the majority of the internals are identical. The 128 uses the same open differential and other internals as the 129, except it doesn't have the viscous coupler around it. It and the 228 are also nearly identical. In other words the 119, 129, 229, 128, and 228 are pretty much identical.

Likewise the 242, 247, and 249 are nearly identical. The 242 has a crazy planetary in it but shares the same case castings and oil pump as the 249 with a shorter case extension. The 247 is essentiall a 249 with a progressive coupler instead of a viscous coupler. New Process based the progressive coupler design directly on limited slip differential designs. It does the same job as a viscous coupler, just superior in longevity, response, and reliabilty.

The 249 is a completely different Viscous Coupler than the old style used in the 119, 129, and 229. It better in alot of ways, but if it fails it doesn't have anything else. The 119 is completely different, it will continue to function just fine without it.

[priya]

Thanks for clarifying Captspillane.

[priya]

What do you guys think of this site. They mentioned they sell trans rebuilds.

http://www.midwesttrans.com/prodlk.html

Thanks to this post by Eagle1984 I found midwesttrans.com sells a rebuilt viscous coupler for my NP119 for $345, I'm going to order one tomorrow.  I contacted drivetrain.com a couple of times but they couldn't be bothered to respond to my inquiry.  Thanks Eagle1984, eggs to you.

[max98059]

why not pull a tcase out of a Cherokee