NP229 Viscous Coupling--What's it do?

[gwinn]

I'm going to have my transfer case overhauled. I've called a few local shops to get an idea of what price to expect. In general, if the viscous coupling is bad, they add about $700 to the job. One shop told me that they replace the VC with something different. They said I'll lose something to do with slippage, but I didn't understand the language. What does the VC do?

[Stuka]

The VC is what allows slippage between the front and rear axles when in 4wd full time mode. In 4wd lock there is no slippage, and you have real 4wd rather then AWD in full time mode. What they probably do is replace the viscouse coupler with a straight through spool, so its always locked. This would mean you would no longer have 4wd full time. So you would have to put manual locking hubs up front. You would end up with 2wd, 4wd lock, and 4wd lo range lock.

[joe]

The VC does allow the function of full-time 4WD as Stuka said and the thing about the options to not use the VC is correct if such a part-time set up even exists for a 229 but $700 for a VC?
Granted they(VC's) are expensive if you can find one(new $300-$400) but since the shop is already inside the case labor is the same so I can't see where the extra $300-$400 comes from over the cost of the VC? If you really want full-time 4WD it's a judgement call I guess as to what it's worth to you but if you can live with part-time 4wd(much more reliable) just swap in an np208 and a rear drive shaft from the donor rig or have your's lengthened.

[ June 11, 2003, 07:07 PM: Message edited by: -joe ]

[Rande]

When a truck turns a corner, the front axle travels in a larger arc than the rear axle does. the two axles start the corner at the same time and finish the corner at the same time but the front axle has to travel farther than the rear axle. That means the front wheels have to turn faster than the rears to get around the corner. If the two axles are locked together, the front can't go faster than the rear and the drivetrain will bind up. On loose surfaces (sand, loose gravel, snow, mud etc) the tires can slip a bit to alleviate the binding. On a hard, high traction surface, this can't happen so the viscous coupling allows for slippage between the front and rear axles so no binding takes place. Its just a limited-slip differential in the transfercase. The earlier Quadratrac used clutches in the transfercase differential and the NP229 and the NP219 use a viscous coupling to do the same job. The NP228 uses an open differential instead of the viscous coupling. It didn't work very well and was used only one year (1986).

In 4HI lock and 4LO lock, the viscous coupling is bypassed and the axles are locked together.

[ June 11, 2003, 07:16 PM: Message edited by: Rande ]

[Thomas DeBusk]

I looked very hard for VC's to rebuild a case about 3 months ago. Jeep dealers wanted almost 800 dollars for the part. I did find an aftermarket source that was selling VC's for $345. They couldn't tell me who made it, though.

Those were the only two sources I found.

Thomas

[irbob]

Cost me $700.02 to rebuild my 229. That includes 350.00 for the VC, all new bearings and seals. No labor cuz I did it myself.

Somthing to do b4 the work is done is to test it to see if it's bad. How to test it is in the servise manual. I don't have it right here with me.

What's wrong with it that u need to overhaul it?

[gwinn]

Other than some fluid leakage, when shifting into 4H the dash light says its in 4H, but the front driveshaft isn't powered up. It will shift into 4L though.

[irbob]

Sounds like a linkage problem.

[fulsizjeep]

Sounds like it could be linkage prob or the VC is really bad. My 229 finally toasted on me in Moab (226k miles on it) back in April and I put a 208 in. It is a very cost effective change over. I got the 208 from one of the front range guys who picked it up at PNS Denver for $60. The rear drive shaft came from a 78 Wag with QT in Farmington for $20.

[SAustinwag]

thats what I need to do... I'm running around with my 229 with no front driveshaft, I hope that I wont screw anything up with the VC. Rockjeep44 told me a couple of weeks ago that It wont.

I've got mix-matched gears in my front/rear axles, so I pulled the front driveshaft. I noticed though, that when I turn the front yoke on the front axle, it free spins.. I guess I coulda left the driveshaft in..?? dunno. I hate xfer case crap.

[irbob]

Let me know if anyone knows of where I can get a trashed 229 with a good back half section. I have sort of a cracked one here i'd like to fix. Thx

[irbob]

bump

[Bob Barry]

Originally posted by SAustinwag:
thats what I need to do... I'm running around with my 229 with no front driveshaft, I hope that I wont screw anything up with the VC. Rockjeep44 told me a couple of weeks ago that It wont.

It won't, as long as you keep it out of 4wd.

Originally posted by SAustinwag:
I've got mix-matched gears in my front/rear axles, so I pulled the front driveshaft. I noticed though, that when I turn the front yoke on the front axle, it free spins.. I guess I coulda left the driveshaft in..?? dunno. I hate xfer case crap.

Your front axle is disconnected. That's what the vacuum-lines going to the front-cover do. '83 and '84 were the only years to use this "feature". If it was disconnected when you put the transfer-case in 4wd, then you probably burnt-up your Viscous Coupler. The stock lines are routed to prevent that from happening, but DSPO's have a way of bypassing factory safety things.