Topic: NP 231 rebuild

[fatoldcapt]

My transfer case is making a "whine" kind of a noise when in 4 Low. It's not noticeable in 4 high or 2 wheel drive.
Should I try to rebuild it? I do have a Shop Manual for my jeep.
What should I look for as the cause of this noise?
Or would it be best / easier to get a rebuild or salvage yard case?

[sharpxmen]

they always make that noise, it's the planetary gear that does it when engaged. Make sure your oil level is correct.

[Torch_Ind]

they always make that noise, it's the planetary gear that does it when engaged. Make sure your oil level is correct.

+1

it will make noise normally!! especially if your doing higher speeds there not meant for that!!

[Jeffy]

I love the gear whine.     Even old Jeeps whine with their gear drive transfer cases.

[Torch_Ind]

I love the gear whine.     Even old Jeeps whine with their gear drive transfer cases.

gear on gear rocks!!

[fatoldcapt]

Thanks! Yeah, the "whine" is most noticeable 4L under load. Coasting, it is quiet. Speed is not such a problem. However I'm used to how it was in my old Toyota PU. I would lock the hubs and throw it in 4L and drive all day. My little jeep won't go all that fast in 4L. Even when I'm in Third of Fourth. I keep shifting in and out of FWD and H&L. Depending on the lay of the land.
I'm glad to know it's okay. The fluid's fine.

[sharpxmen]

everyone else thinks the 4L is too fast on the Jeep - most are looking for a 4:1 t-case, the stock is 2.73:1 - really is only meant for crawling and steep inclines, you should not drive it in 4Low or even 4Hi unless you're offroad (not on paved streets)

[Torch_Ind]

Thanks! Yeah, the "whine" is most noticeable 4L under load. Coasting, it is quiet. Speed is not such a problem. However I'm used to how it was in my old Toyota PU. I would lock the hubs and throw it in 4L and drive all day. My little jeep won't go all that fast in 4L. Even when I'm in Third of Fourth. I keep shifting in and out of FWD and H&L. Depending on the lay of the land.
I'm glad to know it's okay. The fluid's fine.

.

You shouldn't really run 4L in 3-4th gear

[chardrc]

.

You shouldn't really run 4L in 3-4th gear

 i haven't crunched the numbers but im pretty sure 3rd low is lower than 1st high, and Ive found many a situation where you need the speed of 3rd low where 1st high you don't have the power or option to downshift... just saying from a practical standpoint its impractical to limit yourself to 1,2 for low range, although when you want to go to 4th its best to switch up to high range.   

[dwtaylorpdx]

I started running heavy duty full synthetic in the Tcase (ATF) and it got a lot quieter....

Interesting tidbit.... The TCASE is the only power train component in my YJ that has never been opened or rebuilt at 200+ K miles.

Rod Hall ran stock NP231 behind 400+ HP engines in the Baja..

Dave

[fatoldcapt]

Thanks for all the info. Do you have any more info on the Heavy Duty Synthetic you mentioned? Or should I just go shopping at the auto parts and see what I can find?

As to those warnings (from other folks) about using 4L 3rd or 4th. I don't understand the caution. As long as I'm watching the Tach and not over revving it, it should have the same internal rpm if I'm in 1st or 4th. Shouldn't it?

It's just in short desert washes. Climbing up and going down. Across ridges. Tight turns, sand, rocks. I don't enjoy shifting into 4H or 2WD if I don't have to. I have a posi-lock. It really bogs things down when I'm following a bunch of 4.0 TJ's with Automatic trans. I have a 5 spd. And staying in 4L until the trail speed gets up to where I'm thinking about going into 4L 4th gear for a while is what I do most of the time. 4H just doesn't have the poop to do much more that flat ground sand wash with no obsacles.  

[dwtaylorpdx]

I use Amsoil or Redline, Royal Purple has one too...

The main thing is the thermally tougher synthetic that can handle the planetary spin better.

Dave

[fatoldcapt]

Thanks!