NP231 to NP242

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12-25-2018, 02:00 PM

#16

brdavis9

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Join Date: Sep 2011

Location: Spokane WA

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Year: 1996

Model: Cherokee (XJ)

Engine: ERH 4.0L Power Tech I-6 (HO)

NP231 <--> NP242 compatibility summary

I came across this thread while researching a proposed NP242 swap into my NP231-equipped 1996 XJ. I'd already came across the following "compatibility list" on Jeep Forum about year-on candidates for the transfer case swaps (after purchasing an 1989 NP242 that wasn't going to work at all, I wasn't willing to make the same mistake twice LOL) so I thought I'd share.

Anyways... from this thread on Jeep Forum for ZJ swappers, https://www.jeepforum.com/forum/f13/...4/#post6491564 ...I got the following info which is relevant to a couple of comments here.

NP242/NP231 Compatibility Summary

When selecting a transfer case, there are many factors to consider. First, the only feasible swap is a NP231 or NP242 from a JEEP, specifically an XJ or ZJ. Dodge transfer cases will not work, and neither will WJ cases. Dodge cases have a different main shaft and tail cone assembly, and WJ cases have no speedometer sensor provision.
It's best to go by the build date on the transfer case, not the year of the Jeep when determining the gear pitch. Rule of thumb is cases with a build date of pre-1994½ will have the old style gear cut, and cases with a build date of post-1994½ will have the new style gear cut.
Your best bet is to find a transfer case with the same input shaft. If not, you can swap input shafts, but be aware of the annulus gear cut change that occurred in mid-1994. The different gear cuts are easily identified when compared, the late style teeth are much more pointed than the early style, and the late style uses a much more narrow bearing.
There are 3 different input shafts, .750", .840", and 1.55", as well as both 21- and 23-spline shafts. All ZJ transfer cases have a 23-spline input shaft, and all 1992-2001 XJ's have a 23-spline input shaft. 1991 and older XJ's have the 21-spline input shaft.
Here's a general rule of thumb when determining your input shaft length. (This is not always 100% accurate, so make sure you know what you have before buying a transfer case.)

1993-1995 V8 ZJ's: 46RH transmission, 1.55" 23-spline input shaft
1993-1995 I6 ZJ's with the 42RE: .840" 23-spline input (with collar)
1993 I6 ZJ's with the AW4 or AX15: .750" 23-spline input
All 1996-1998 ZJ's: .840" 23-spline input
All 1996-2001 XJ's: .840" 23-spline input
1992-1995 XJ's: .750" 23-spline input
1991 and older XJ's: .750" 21-spline input

From following the above rules, I figured that the NP242 from his 1998 Grand Cherokee a local guy was selling on C/L (with 147K at the time it was pulled) would be a pretty good fit for my 1996 XJ (bonus: about 20K fewer miles too). I read this advice to mean that – in my case – I should look for a Selec Trac from a 1996-2001 XJ or from a 1996-1998 ZJ for the fewest possible compatibility issues. So I bought it (and yeah, I have no need for the 1988 NP242 of unknown provenance if you have a need).

NOTE: All credit for the above info is due the OP on the Jeep Forum thread: JrMechanic. I just edited his info a bit for clarity before copying it here.
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Note: The reason for the swap to Selec Trac from Command Trac: our XJ is a winter DD, and not an off-road crawler, and I wanted a full time 4WD option to make snow driving less problematic for my wife.

Now all I gotta do is find a Select Trac shift gate and bezel... which, if anyone has those, I'd be willing to swap the NP231 versions straight if you're interested.