[Guest]

About 2 months ago I tore apart my YJs NP231 after determining that the driveline catching and grinding was happening internally. I found that the Range Shift Fork and Range Shift Hub were all chewed up and the source of my worries. I bought an NP231 with about 40K miles on it, and about 50 of those used off-road. I took out the compatable parts, replaced them, put it all back together, and it worked like a charm!

About 800 miles later, the Range Shift Fork has crapped out yet again (had to tow my rig from the Adirondack Mtns 3 hours home, quite the ride). I tore the Tcase apart once again and the Fork looks as if the Range Shift Hub was rotating real hard and fast, and grinded the Fork like a mill. I dont want to put it back together with a brand new Fork if its just gonna fail and require another rebuild. Now, I bought it with about 50K on it, and Ive put about 60K on this YJ, highway and trail miles, for the past 4 years. It has had 4" suspension and 33x12.50 BFG A/Ts on 15.5 wheels since I got it. My questions are as follows:

1. Has anyone had similar problems, or experience this with the NP231 or any other Tcase?
2. Could it just be worn down input and output bearings?
3. Does the Range Shift Hub rotate?
4. Is there something Im missing?
5. Does anyone have a Range Shift Fork floating around theyd like to get rid of, or a parted NP231. Im also willing to trade parts off my 2nd case.
6. Have the Tcase and its components seen their days with the added stress of the lift, wheels and tires?

Sorry so long, just wanted to make it clear. This is the 2nd time Ive had this thing in parts, and Id like to make it work longer than 800 miles. Any feedback is greatly appreciated. Thanks!

Jason (Im going through Jeep withdrawel, and as if the DTs werent bad enough, my only other rig is a Toyo Corolla

) Dunn

 

[WILL]

I had a friend that had a similar thing happen. The mode fork on that one was worn down to nothing though. Aren't there some plastic pads on the forks to keep that from happening?

 

[Guest]

yeah, those little plastic pads were swimming in the bottom of the Tcase fluid along with some pieces of the Fork. I see what youre saying, but something is vibrating itself so violently, that its destroying not only the pads, but the fork as well.

 

[WILL]

If the pads were in the bottom of the case, then the fork self destructed because they fell out. Now you just need to find out why they fell out.

 

[Guest]

hmmm, interesting thought. Now that I think back, those pads could have been pulled off pretty easily. Which leads me to question why they are not secured to the fork. Are the pads casing the fork and hub to fail, or are the hub and fork causing the pads to fail. damn chickens and eggs. Ill look at the pads a little closer.

Also, I just remembered another forensic clue: the second fork I used was aluminum, whereas the first was steel. The steel looked as if it was grinding. The aluminum looked as if it was chewed, then melted. This leads me to believe that the shift hub was rotating at a high velocity, fast enough to melt aluminum. Just before the fork failed on the highway, I smelled a burning odor for about 4 seconds, and then it no longer went in gear. Just another piece of the puzzle.

BTW, thanks for the quick reply. This is making my work day fly.

 

[959]

it seams to me that the fork should not be touching anything with any force, while you are driving. If the aluminum was chewed and melted that means the fork must have been pushing on something hard. the heat was cuased by friction.

is there any binding in the linkage, was it easy to shift?

are you running ATF or 90 weight in the T -case?

ATF

do you have stock gears? 3.07s so are you doing allot of driving in 5th gear in low range? just a question. cuase I do it.

 

[bandhmo2]

You might find this artical interesting. It is about NP241 but they opperate the same so it likely carrys over.

 

[WILL]

The pads should fit in a notch in the fork. When the fork is on the sliding collar, the pads can't move away from the fork to fall off. If the pads you found in the bottom are still perfect, either they fell off during reassembly or very shortly after.