« Reply #4 on: June 05, 2012, 02:10:49 AM »
You must have the silicone fluid in the viscous coupler for it to be able to work. This fluid is retained by a single O-ring. All the cases I've opened had globs of the thicker silicone fluid at the bottom of the case because it leaked out past that O-ring. Once that O-ring fails and the silicone fluid leaks out the viscous coupler is a fancy paperwieght. If you drain it during the rebuild process then you just destroyed it in a sense. No replacement fluid is available anywhere because its toxic and out dated.
The good news is that the viscous coupler has an open differential incorporated into the design. The car drives perfectly fine without it. In fact a 1986 Eagle or Full Size Jeep will have the exact same transfer case except the viscous coupler is eliminated. Those are called NP128 and 228. Few customers knew the difference. The all wheel drive is still much better than rear wheel drive in every driving condition even without the viscous coupler.
In later Jeep Grand Cherokees they made the 229. It has a different viscous coupler without an intergrated open differential. When it fails the vehicle must be towed. The smaller 249 viscous coupler is much more robust and reliable however than a 229 unit. It has much more than the dinky O ring keeping the fluid inside it. Because its smaller, the extra room in the case allows for a nifty oil pump that circulates transfer case fluid better than the older cases. The 229 was replaced by the 247. The 247 has a more durable limited slip differential that does the same job as a viscous coupler except faster and without the toxic silicone fluid.
I personally am scrapping all my old 129's. I only use the NP242. It's a very easy and cheap conversion. I used my original driveshafts without any welding or fancy modifications. A 247 is a great choice too but I value the two extra functions that the 242 has more than the 247 traction benefits. Do not use a 231 or a 241. A 249 works well and are common but the New Old Stock viscous coupler's are already expensive and they will never be made again. They'll continue to get expensive and rare. Avoid a 249 from an early year of production because they do not have a fully locked 4 wheel drive. You might need that to limp home if your VC burns out.
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Topic: Where to find parts to rebuild/fix Transfer case (Read 8332 times)