NP231 transfer case differences?

[Erik V]

Is there any difference between a NP 231j T-case that was mated to either a Automatic or Standard trans? Both behind a 6cylinder and same year TJ, 06.

I was thinking about buying a T-case ( I found one for $100) and doing a sye and any other maintenance on it and when all complete throw it in when I got time.

It’s my daily driver and id like to have minimal down time as possible.

Thanks

 

[Erik V]

Anyone?

 

[glwood]

Reasonable question. I wish I had your answer, but I have a Rubicon, and don't have a 231. Someone will chime in, I'm sure.

 

[Jerry Bransford]

Is there any difference between a NP 231j T-case that was mated to either a Automatic or Standard trans? Both behind a 6cylinder and same year TJ, 06.

I dunno about your model year but the transfer case input shaft length is different depending on if the transmission is an automatic or manual on earlier years. I imagine they're still different on your '06. It is possible to change the input shaft but it's not an easy job.

 

[Chris]

The only difference would be the input shaft length and spline count.

This is taken from Novak's website in regards to the NP231 transfer case:

The important variations to look for in the 231 transfer case are in the input gear. The 231 comes in 21 spline and 23 spline versions with long, medium (rare) and short variations.

The long shafts protrude 2.1" from the front mounting face of the transfer case. The short version protrudes 1.2". The rare medium shaft protrudes 1.7". You should be careful when swapping any of these gears due to different bearing widths and gear teeth. The following chart shows how to determine which input gear you might have by transmission. It is always recommended to verify first hand if possible.

Because of differences in the cut of the gear, as a general rule, one should not interchange 1987-1993 gears with 1994-present gears. These years are not always hard and fast delineations. If one is not absolutely certain, disassembly and inspection is required.

Note that some transmissions change spline count. The Peugeot BA10/5 had both 21 or 23 splines. The AW4 had 21 splines through 1990. In 1991 (the same year the 4.0 HO was introduced) the AW4 splines increased to 23.

Be certain, in any interchange situation, that you select the right length of input gear for the factory style transmission being used; e.g., a long input gear against an AX15 (usually requiring a short input gear) will cause interference at the end of the splines and put damaging thrust pressures on the transmission mainshaft and transfer case input gear.

 

[ac_]

I dunno about your model year but the transfer case input shaft length is different depending on if the transmission is an automatic or manual on earlier years. I imagine they're still different on your '06. It is possible to change the input shaft but it's not an easy job.

Jerry, are you sure? I have been researching this myself also, and when ordering online they don't ask if it is an auto or man. They only ask if you want the to supply a driveline and what kind of yoke is all. Unless I am missing something?

 

[ac_]

The only difference would be the input shaft length and spline count.

This is taken from Novak's website in regards to the NP231 transfer case:

The important variations to look for in the 231 transfer case are in the input gear. The 231 comes in 21 spline and 23 spline versions with long, medium (rare) and short variations.

The long shafts protrude 2.1" from the front mounting face of the transfer case. The short version protrudes 1.2". The rare medium shaft protrudes 1.7". You should be careful when swapping any of these gears due to different bearing widths and gear teeth. The following chart shows how to determine which input gear you might have by transmission. It is always recommended to verify first hand if possible.

View attachment 36931

Because of differences in the cut of the gear, as a general rule, one should not interchange 1987-1993 gears with 1994-present gears. These years are not always hard and fast delineations. If one is not absolutely certain, disassembly and inspection is required.

Note that some transmissions change spline count. The Peugeot BA10/5 had both 21 or 23 splines. The AW4 had 21 splines through 1990. In 1991 (the same year the 4.0 HO was introduced) the AW4 splines increased to 23.

Be certain, in any interchange situation, that you select the right length of input gear for the factory style transmission being used; e.g., a long input gear against an AX15 (usually requiring a short input gear) will cause interference at the end of the splines and put damaging thrust pressures on the transmission mainshaft and transfer case input gear.

Oh I see if you are going to change years?

according to matrix above it looks like it is all the same except the older manual trans and 1 older auto if I am reading it right. Other than those few they are all the same? Am I reading that right?

 

[Chris]

Oh I see if you are going to change years?

according to matrix above it looks like it is all the same except the older manual trans and 1 older auto if I am reading it right. Other than those few they are all the same? Am I reading that right?

The older manuals are all 21 spline while all the autos are 23 spline. The only difference is the newer 5 and 6 speed transmissions (the Mercedes gearboxes) are 23 spline and long input shafts.

That's how I read the chart.

 

[ac_]

The older manuals are all 21 spline while all the autos are 23 spline. The only difference is the newer 5 and 6 speed transmissions (the Mercedes gearboxes) are 23 spline and long input shafts.

That's how I read the chart.

Ok so to answer the @Erik V's question and mine, there actually isn't a difference in an auto or manual 231J in 2006. I don't think any of those trans.(21splines) are even in TJ's right? If we are reading that matrix right.

 

[Chris]

Ok so to answer the @Erik V's question and mine, there actually isn't a difference in an auto or manual 231J in 2006. I don't think any of those trans.(21splines) are even in TJ's right? If we are reading that matrix right.

A 2006 with an automatic transmission would have a 23 spline short input NP231. A 2006 with a manual transmission would have a 23 spline long input NP231.

So while the spline count would be the same, the length of the shaft would not.

This is of course according to Novak (and that chart above). Novak is a trustworthy source though, so I would believe it.

 

[ac_]

A 2006 with an automatic transmission would have a 23 spline short input NP231. A 2006 with a manual transmission would have a 23 spline long input NP231.

So while the spline count would be the same, the length of the shaft would not.

This is of course according to Novak (and that chart above). Novak is a trustworthy source though, so I would believe it.

Haha ok you're right I was confused. I was hung up on the spline not the shaft sizes. Sometimes I need a ton of bricks to hit me.

 

[Chris]

Haha ok you're right I was confused. I was hung up on the spline not the shaft sizes. Sometimes I need a ton of bricks to hit me.

I hear ya! From what I understand though, changing the input shafts isn't that difficult of a task.

 

[Jorge Bolivar]

Is there any difference between a NP 231j T-case that was mated to either a Automatic or Standard trans? Both behind a 6 cylinder and same year TJ, 06.

As far as I do check for mine 03-06 are the same NP 231 for both transmissions but not hold my breath over it. Hope some one can solid confirm.

I was thinking about buying a T-case ( I found one for $100) and doing a sye and any other maintenance on it and when all complete throw it in when I got time.

Save that money for the new driveshaft and avoid yourself a headache.

It’s my daily driver and id like to have minimal down time as possible.

Doing the SYE is fairly simple, more simpler if you removed from the jeep and do it on a bench, not much room for errors either. The maintenance work changing the usual components will be done as you install the new SYE components. Probably will expend more time removing and re installing the transfer case than installing the SYE.

Thanks

 

[Erik V]

Ok so if I look for another NP231j T-case I have to make SURE it’s from a Automatic transmission (as mine is) and the same year, ( 06 )?

That’s what I’m getting from the above posts.

 

[Chris]

Ok so if I look for another NP231j T-case I have to make SURE it’s from a Automatic transmission (as mine is) and the same year, ( 06 )?

That’s what I’m getting from the above posts.

Yes. But even if it isn’t, swapping the input shaft isn’t a big deal, it’s actually pretty easy from what I’ve read.

 

[Erik V]

I get that it might be easy to swap the shafts but I was wanting to do a sye and rebuild on another T-case and just throw it in without having to do it to mine.
Looks like I’ll just have to bite the bullitt and just do mine instead. So much for no down time.

 

[ac_]

I think what he is saying is if you do get the wrong transfer case and you need to change the shaft it wont be hard. Meaning you can do it on your spare. If you look at the matrix you can also get it from a different year I believe. Just a newer one probably preferably from an auto so you don't have to change the shaft. Seriously though, I did a SYE in one day in my garage with hand tools from start to finish by myself. I am mechanically inclined though, I don't know your expertise.

 

[Chris]

Funny... that chart doesn't mention anything about the NP231 behind the 42RLE transmissions.

 

[Erik V]

I think what he is saying is if you do get the wrong transfer case and you need to change the shaft it wont be hard. Meaning you can do it on your spare. If you look at the matrix you can also get it from a different year I believe. Just a newer one probably preferably from an auto so you don't have to change the shaft. Seriously though, I did a SYE in one day in my garage with hand tools from start to finish by myself. I am mechanically inclined though, I don't know your expertise.

I have no problem doing the work, I spin wrench’s for a living, lol.
With my experience it seems nothing goes smoothly on old stuff and I figured if I had a extra case and something went wrong I’d still be able to drive my Jeep.

 

[healsonwheels]

Funny... that chart doesn't mention anything about the NP231 behind the 42RLE transmissions.

Sorry for the bump, didn't want to start over. My '05 LJ with 42RLE and 4.0L just had it's transfer case get destroyed today (front driveshaft seized... thanks sparrows), so I've been thoroughly confusing myself on the internet looking for a replacement.

You said above "A 2006 with an automatic transmission would have a 23 spline short input NP231. A 2006 with a manual transmission would have a 23 spline long input NP231. "

but as you also noted, the chart doesn't mention the 42RLE. Wouldn't a 2006 auto (42RLE) possibly be long input? I've seen it stated both ways