Transfer Case help

[priya]

i am wondering the same thing about my np119.  i changed the fluid and i had think gray stuff dripping out of the case ater all the rest of the fluid came out.. is this the vc fluid.  i was reading on here that when the vc fails it acts like an open differential.  does that mean it still works more or less?  im a little confused on that. 

Yes that means it still works fairly well.  There was one year of Eagle that came with an open differential so the factory thought that worked well enough for a new 4 wheel drive vehicle.

[carnuck]

Yay! Board is working again! If you need a VC or a NP129 tcase I have both for sale. It's even working for my phone!

[captspillane]

i was reading on here that when the vc fails it acts like an open differential.  does that mean it still works more or less?  im a little confused on that. 

The Subaru version of All Wheel Drive is open differential. With your empty viscous coupler your Eagle still performs better than a Subaru, it's tougher than a Subaru, and is capable of getting the exact same gas mileage for a third the maintenance cost as a Subaru.

Today only top end all wheel drive cars have limited slip differentials in their full time transfer cases, and they all use different technology to accomplish it. The Eagle was the first AWD car and it was quite advanced even by today's standards.

[jspeez13]

now that the captain has spoken i feel better about not getting stuck on the beach while surfing a noreaster in december.  however, my brain is fried trying to figure out how it works with no fluid in it.  i would like to have a fully functioning unit this one has 130k on it. 

[captspillane]

The Eagle in stock form without a viscous coupler is amazing in snow and I've driven around several stuck wide tire trucks with ease. It does work rather well as is.

The only time you'll see one wheel spin is if it has absolutely no resistance to it, and that is not common in real life. Any resistance to the wheels at all, even just slight brake pressure, creates a torque split. If the car is moving you won't be able to know if the Viscous Coupler is working or not. Anything over 15 mph its impossible to get one wheel to sit still while the other spins because a wheel can't just stop while the car is still moving forward. As long as all the wheels are spinning all of them are getting some of the torque.

If you try to move very slow while offroading the stock Eagle transfer case is useless. Even a NP219 is near useless. They are meant for driving on a road in severe conditions, not crawling through mud. The first time you sit still with weight off one wheel you won't easily get it to start moving again. I plan on moving slow so any transfer case without a fully locked transfer case option is useless to me, and only one exists with an all wheel drive mode available. It's called the NP242. I personally am going NP242 in nearly all my Eagles. It has an open differential for responsive all wheel drive going down the road or going fast in sand. If I come to a complete stop in the sand, it will have a great deal of trouble starting up again. For that I pop it into "full time" and I have a fully locked transfer case as well as a fully locked low range.

Jeep also has an LSD transfer case commonly available today. The NP247 directly replaced the NP249. It has a LSD that works a thousand times faster and more reliably than the 249's Viscous Coupler.

[captspillane]

my brain is fried trying to figure out how it works with no fluid in it.

An Eagle viscous coupler is shaped like a donut. One half of the donut is splined into the forward output of an open differential and the other half of the donut is splined into the rear output of the open differential. The open differential sits in the middle and works completely independent of the viscous coupler. If in normal operation it lets the forward and rear outputs spin at different speeds in relation to each other, then the two halves of the donut splined rigidly around them must also be spinning at different speeds than each other. If you have no fluid they will just sit and spin along for the ride. If you have a 1986 Eagle there is just a space filler and nothing will happen either. In 1986 only AMC eliminated the Viscous Coupler in all Eagles because it was too expensive for what it was worth. Every other part in a 1986 NP128 transfer case is exactly the same as a NP129. That is testament to the ability of the open differential to operate on its own with or without a working viscous coupler.

If the outputs are spinning at different speeds and in turn the halves of the donut are spinning relative to each other, the fluid inside the viscous coupler will start to heat up as the plates inside the viscous coupler slide in close proximity to each other. As it heats up the fluid's viscosity increases and that makes it heat up even faster. As it heats and increases viscosity it puts increasing pressure on the internal plates to stop spinning relative to each other, which in turns puts increasing pressure on the two donut halves to lock together which in turn slows and stops the difference in transfer case output speed. It is designed to not lock up immediately and to need time to heat up before locking up.

The idea is to let the front wheels spin slightly faster or slower than the rear wheels in turns and other normal driving conditions without a problem. Only if you are stuck spinning your tires wildly will the fluid have the time to heat up and start working. In my NP242 equipped Eagle I have to reach down and use a lever to manually lock the transfer case. AMC managed to design the Eagle to lock up automatically without any driver input. That's impressive. Its especially impressive that they did it in 1980 before any such technology existed.

In a fully locked transfer case powers is always applied to both axles evenly because the outputs spin locked together, so you can drive with or without either driveshaft. If however, you remove your front driveshaft while locked in all wheel drive in an Eagle you will have an extreme difference in wheel resistance between the front and rear. The bigger the difference in wheel resistance the bigger the torque split, with torque taking the path of least resistance. In an open differential the output with the least resistance gets the most power applied to it. The car won't move with the front driveshaft removed until the fluid heats up and locks the outputs. You'll be able to drive about 20 minutes before the heat expands the fluid so much that it blows the O-ring and your viscous coupler is damaged. Once it dies the car won't be able to move again. The more power you apply to the transfer case the faster the front driveshaft yoke will spin while the rear sits idle. Removing a CV shaft will do the same damage.

The silicone fluid is retained by a single pathetic O-ring. That O-ring is 30 years old. It will leak out. What if you try to fill it? Even if you could buy the special silicone based oil used as fluid you would need to know how high to fill the Viscous Coupler. It cannot be fully filled or it will lock up immediately and not allow the thermal expansion, instantly damaging it. Not enough fluid and the thermal expansion isn't enough to lock up and work correctly. The New Process fluid is toxic and no longer for sale anywhere. The Technical service manual doesn't give any information about how to do this. A similar VW version of the fluid may still be available and may work, but I've never seen a vendor and it may be literally illegal to sell it as well. The VW version has instructions with it for rebuilding and refilling, but no such information is available from New Process for our transfer case. You would need to heat it in an oven to a specific temperature and then apply a torque wrench to measure the holding strength at precisely that fluid level and that temperature, neither of which are published specifications using fluid that is illegal to produce or sell. It's essentially impossible.

The only other viscous coupler transfer case that exists is the NP249 used in Jeep Grand Cherokee's. That VC looks more like a soda can than a donut. The open differential is eliminated and the Viscous coupler is the only component connecting the engine to the rear axle. If it wears out the Jeep will act as if it's transmission is slipping. Eventually the car will stop moving if it totally fails. The good thing about them is that the fluid is retained by a welded plug from the factory. It won't leak out. It only fails if the fluid burns out from high mileage. Eventually the NP247 came out with a LSD doing the same job as the viscous coupler but faster, longer, and better in every way. That is the transfer case to use if you want the Eagle to drive and function exactly as AMC intended.

[TheWraith]

...I personally am going NP242 in nearly all my Eagles...

Captspillane, not to hijack but curious as to what you are using for a np242 SYE.  I'm going this route:
http://www.go.jeep-xj.info/HowtoSYEconversion.htm

Hope it is ok to put that link on here.

I'm not going to cut the output shaft myself as the author does in his article.  Instead I intend to have a local machine shop cut it and drill it for me.

Thought you, or others, might find this helpful.  Sorry for hijacking.

[jim]

For those who haven't seen one, this is the vc from my 83 wagon.





I think I still have it around here somewhere.  I can make someone a good price for it.

[captspillane]

Thanks Jim for those pictures. It shows the teeth in the front and back of the donut that spline to the front and rear output of the transfer case, and it shows the open differential nestled in the center. They are exactly the pictures I needed to make my description easier to understand.

Thanks Wraith for the link. I'm not sure if I'm going to go that route eventually or not. My Red SX4 has had a NP242 since 2006. I used the slip joint from a 1992 era XJ that came with the transfer case. I found out that the slip yoke Ujoint was exactly the same size as the Eagle Ujoint and mated the two like it belonged there. The original slip joint in the Eagle driveshaft needed to be disabled. For that I unscrewed the grease collar and popped the end off the splines. I inserted a piece of handrail that hammered perfectly snug around the splines and put it back together. This is the finished product. With this modified Eagle driveshaft I had no noticeable vibration and minimal cost or hassle. I still have a ten foot section of that handrail pipe I found for free. The NP242 was abandoned at a junkyard after someone pulled the transmission. I picked it up and walked out with it for $45 along with the driveshaft. It was nearly a direct bolt in, making it one of the cheapest and easiest upgrades I ever installed. The exception is that I never installed a shift handle, so it was left in all wheel drive the whole time I drove it. I do not know the best or cheapest route to install the handle. I'm playing with an Advanced solid shifter intended for an NV3550 and looking at the Novak cable shifter. I might attempt to make my own if the solid shifter doesn't work for me.

[eaglefreek]

  Even a NP219 is near useless. 

Not if you put it in 4 low.

[jspeez13]

capt.

"If I come to a complete stop in the sand, it will have a great deal of trouble starting up again. "


this is exactly what i will be using mine for.  drive to beach, drive on beach, park, surf, drive off beach.

now im back to being worried about my transfer case.  i think i need to get a fully functioning unit somehow.

[captspillane]

Low range is the single most important upgrade you can perform. The difference is extreme. Every Eagle should have had a NP219 from the factory. In light sand my 2.35 axle ratio Eagle sedan got stuck because the transmission refused to move the car no matter how high I revved the engine. Not a single wheel broke free and spun, it just sat there as if I was holding the brake down. The car didn't stand a chance without low range no matter which transfer case was there. I cannot recommend the 219 but it's obviously a huge upgrade to the 119.

I also put driving in sand as a very high priority. My Jeep Rubicon needed low range and all four lockers working feverishly to get going on the Beach. The wide tires create terrible rolling resistance and plow sand ahead. No matter how knobby and cool looking big tires are they are absolutely terrible in snow and sand. Eagles perform much better than Jeeps because of their stance and thin tires. I simply needed a low range, a fully locked 4high, and a positraction rear to make my Eagle put the Rubicon to absolute shame on the beach.

If you go with a Viscous Coupler transfer case you will be relying on that to lock your outputs consistantly and effectively over the entire trip out on the beach. This is not realistic. The 119 and 219 version is not reliable or robust. If you consistantly heat it you will blow the Oring and send the critical fluid into the case, where it is abrasive to the bearings. The 249 Viscous Coupler has a much longer duty cycle but it has a terrible reputation. It is known to get very weak and pathetic with moderate mileage on the car.

I firmly believe a selectable locked output is necessary for a vehicle consistantly used in low traction situations. Specifically if its used for a long period of time. The 219 coupler was not designed to lock up for hours, only to be a responsive aid in poor road conditions. Having disassembled one, I do not trust it to last any degree of abuse and thus cannot recommend it.

With my 242 I lock the outputs when driving on the sand and bear no worry of damage or wear. I have low range at demand. I have effective all wheel drive while on the road. I have a 2 wheel drive mode for towing conditions. The transfer case is very common and cheap to replace, a huge advantage to the 219. The 242 has an internal oiling pump that the 219 does not. The 4Lo is fully locked, which puts it on par with the 231 in slow speed crawling. It is a very easy upgrade and it offers a great deal of diverse advantages over the other choices.

The absolute best plausible transfer case would be a 242 front half mated to a 249 rear half. They share the exact same casing halves and look identical until the tailshaft extension, where the viscous coupler is added. The two of them share the exact same case and use the exact same splines in the exact same spot, but on the 249 those splines just keep going further instead of stopping early on the 242. I looked seriously at this possibility by tearing down two of them next to each other. It is easy to see how it could be done. The problem is you would literally have to cut each mainshaft and join them precisely together. If I had the tooling to machine my own mainshafts I would do exactly that. It is literally the single piece that would have to be custom made, everything else would be stock components from one or the other. Imagine if the full time 4wd had a viscous coupler as well. It's easy conceptually to accomplish.

[jspeez13]

Well I guess I start shopping for a 242 today. The sand is deep and rutted where I go. Hey capt. Will the 242 bolt up to a sr4 tranny any mods needed there?  Did I read correctly that you just cra under the car to lock the 242 transfer case.  I'm convinced that my 119 isnt going to cut the mustard.

[mudkicker715]

I had a 242 behind my sr4. i took it out to put the 242 in another eagle

[jspeez13]

Good I'm really hoping it just bolts in. I spent money on a new clutch and got a low mileage sr4 from a nest member.  How did you work the shifter?