HELP!!! NP231 nightmare

Ok, I need assistance fast. Here's the deal, I have a 96 XJ sport with a 231. Lately, it started making all kinds of rattling on accel and mostly on decel from the transfer case. So, I found a freshly rebuilt 231 from an unknown year XJ for $200. It is the only one around here without a wait that I can find. Well, I dropped the old 96 231 case to find that the chain is not worn and it looks to be OK. I already own the re-built 231, so I might as well toss it in.

Of course it wont fit,the input shafts on the re-built one are smaller than the busted one. Here are my questions

1. What the heck was making my old transfer case make all the noise? It got worse when 4wd was ingaged.

2. Can I use the input shaft from my 96 231 on the new 231? If so, do these gear-sets ever wear out? I have the 96 Input shaft already out.

3. The truck was lifted before I bought it. Is it supposed to have an aluminum rear drive shaft? Because it does............

4. Can I use something other than ATF in the 231? Is there something better to use?

5. Other than the input shaft, are these transfer cases the same? Both were stamped 231 J? I have the speedo gear and two wire electical switch hooked up to the "new" 231 already.




No, I cant take the "new" 231 back, I own it. I need to get this truck on the road tomorrow. Thanks for the help!!!!!!!!!

tnomud said:

Ok, I need assistance fast. Here's the deal, I have a 96 XJ sport with a 231. Lately, it started making all kinds of rattling on accel and mostly on decel from the transfer case. So, I found a freshly rebuilt 231 from an unknown year XJ for $200. It is the only one around here without a wait that I can find. Well, I dropped the old 96 231 case to find that the chain is not worn and it looks to be OK. I already own the re-built 231, so I might as well toss it in.

Of course it wont fit,the input shafts on the re-built one are smaller than the busted one. Here are my questions

1. What the heck was making my old transfer case make all the noise? It got worse when 4wd was ingaged.

2. Can I use the input shaft from my 96 231 on the new 231? If so, do these gear-sets ever wear out? I have the 96 Input shaft already out.

3. The truck was lifted before I bought it. Is it supposed to have an aluminum rear drive shaft? Because it does............

4. Can I use something other than ATF in the 231? Is there something better to use?

5. Other than the input shaft, are these transfer cases the same? Both were stamped 231 J? I have the speedo gear and two wire electical switch hooked up to the "new" 231 already.




No, I cant take the "new" 231 back, I own it. I need to get this truck on the road tomorrow. Thanks for the help!!!!!!!!!

Click to expand...

The input shafts are probably 23 and 21 splined units respectively.
I have swapped the units myself, as well as helped another person do it via telephone. They will interchange. You will need to do some measurements from the crown of the input shaft to the base of it to ascertain whether they are identical.

As for the driveshaft, it is my understanding that aluminum is somewhat more tempermental than steel. The hard fact is that you need a SYE kit to eliminate a steep operating angle that the lift has created. Or you could drop the truck back to original condition (although I'm a big proponent of actually installing the SYE on stock rigs, so poor was the original design of the rear driveline in XJ's)

Worse in 4x4? You double the torque in the 4WD mode. It is also possible that the front driveline is in need of realignment of the pinion after the lift was finished. Because it's a 96 model, your front driveline is in movement all the time, but in 2WD mode, it is driven by the front wheels, not the transfer case. If there was a serious issue with the pinion, I suppose you'd feel it before the 4WD was engaged.

There also may be an issue with the rear driveshaft length. 1996 was a crossover year, and some transfer cases were the pre 1996 "short" rear output, and some were the longer 1997-01 output/sealed type.

The proper lubricant for the case is always DextronIII. The small pump in the rear operates only with that viscosity.

Hope this helps.

1. How sure are you it is the tcase? 96 XJ is hard to believe the tcase is just bad.

2. It will depend on the year of the new tcase. Input gears and ring gears can be different and will make noise if they are mixed.

3. Get rid of the aluminum drive shaft. Just my opinion, just doesn't sound good for a 4x.

4. Only if you want to destroy your tcase. Use atf!

5. Basically yes, but might have some production parts that are different but do the same thing. (just made differently but are mainly interchangeable)

mark

Well, I ran into some surprising stuff. The transfer case seems to be ok. There were no shavings, no chain marks in the casing, and the fluid smelled good. I took the planetary gearset to a tranny shop and they say is totally within specs. So, I slapped it all back together and the mystery noise is still there.

Could this be driveshaft vibration? It does look like it is at a wicked angle on the rear? The noise sounds like a wicked exhaust rattle. It vibrates on throttle, and rattles off throttle. The tranny is not slipping and the rear end is fine.

I am fed up..............

Front driveshaft u-joints??

Rev

tnomud said:

Well, I ran into some surprising stuff. The transfer case seems to be ok. There were no shavings, no chain marks in the casing, and the fluid smelled good. I took the planetary gearset to a tranny shop and they say is totally within specs. So, I slapped it all back together and the mystery noise is still there.

Could this be driveshaft vibration? It does look like it is at a wicked angle on the rear? The noise sounds like a wicked exhaust rattle. It vibrates on throttle, and rattles off throttle. The tranny is not slipping and the rear end is fine.

I am fed up..............

Click to expand...

Got a angle finder? Anything over 12* is pushing it. You'll either have to install a SYE to shorten the output, or drop the truck back to stock. In either case, I'd definitely replace the output shaft bearing in the rear of the case. I've seen them howl when they actually look just fine.

Also look at the possibility that something was welded inside of that aluminum shaft tube and finally fell loose inside it??? :anon: Aluminum is famous for excellent conducting properties in audible frequency.