NP231 transfer case differences

Chris

Administrator
Staff Member
Ride of the Month Winner
Joined
Sep 28, 2015
Messages
70,955
Location
Florence, AZ
Just wanted to make an official thread about this, since the topic seems to come up from time-to-time.

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.

Screen Shot 2018-03-25 at 8.54.59 PM.png


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.
 
From Advanced Adapters, I'm still looking for Short/Long & manual/Auto trans differnces.
G. 42RLE 4 Speed Auto
42RLE
This transmission was used in the Jeep Wranglers in 2003 through 2011. We currently do not offer any engine conversion adapters for this transmission. We have installed several Atlas transfer cases to this transmission. The rear section of this transmission is the same circular bolt pattern with a 23 spline output.

Only option from Rock Auto for Input Shaft:
Trans. code 42RLE; Trans. code NV3550; NP231, NP242 & NP249 Transfer Case Input Shaft; 95 & Up; 23SPL, 4.25"

Not sure if this is helpful or not, I can't make sense of it.
 
  • Like
Reactions: Chris
I'm going to label this a hopeful helpful. My wife is upgrading to a rubicon tcase and I am taking her SYE for my LJ. She has the Nsg370 and I have the 42RLE. I am pretty sure the NV3550 and NSG370 have the same input shaft so therefore the 42RLE should be the same as well... We will see. This way I can just plainly swap tcases and not have to rebuild the SYE...
 
  • Like
Reactions: Chris
Preferred fluid?
ATF+4
Novak claims Straight 30 or 5W30 in a mineral or synthetic.

I’ll be getting this next, as soon as I rule out some vibration issues.
 
I have my case open now if there are any requests for spline counts, I only have the back half open, no reason to pull the entire case out yet.
 
Reviving this about the Rubi TC swap. Rubi case is short input, (I measure 1 3/8) and the 231 I took out of my 02 Sport with a 3550 manual, is long input, (2 1/8)
Am wondering if that is enough shaft contact and are the two input shafts interchangeable if I wanted to swap. Involves splitting both cases, not attractive.

Just another reason to swap to an AX15 while at it I guess, give another half an inch contact. What you think ?