Sorry if this has been discussed a lot, but I still dont know what to get after readind every post I could about this subject...
I would like to do this swap (np231 or preferably np242) to get the locked front/rear in 4lo, but the more I read, the more I get confused about wich transfer case I should get. I have a 94 V8 with the 46RH trans, so I probably have the 1.55" 23 spline input shaft. I know that I will have to swap the input shaft, wich is fin with me. What is confusing me is the Annulus gear change that occured in 94.5. What happen if you get a transfer case with a different gear? Can you simply use the cover of the 249 on the 231/242?
I cannot tell you if my 249 is pre 94.5 or post 94.5 as my jeep is far right now, but I would really appreciate if someone could clarify this for both cases : from wich jeep can I get a np242 or np231 at the junkyard? My only criteria is to get one that wont necessitate me to get to the dealership to buy new parts... I would like everything such as the driveshafts, shifter linkage and 4wd switch to plug back without issues.
Thanks a lot !
Taken from the first post of this thread
The NP242 recipient is my buddy's 93 ZJ with the 5.2/46RH/249 with the long input shaft. The 242 donor was from a 92 XJ with the short style input shaft, meaning it was required for me to swap input shafts.
NP231 or NP242 from an XJ or ZJ.
NP231: Part time transfer case used commonly in XJ's, YJ's, TJ's, ZJ's, etc. It offers 2wd, 4 part time, and 4 low.
NP242: Full Time transfer case used in XJ's and ZJ's. 2wd, 4 part time, 4 full time, and 4 low. The 4 full time feature is unique from the NP249 as it does not use a vicious coupler (what goes bad in the 249), but instead a mechanism similar to an open differential.
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 92-01 XJ's have a 23 spline input shaft. 91 and older XJ's have the 21 spline input.
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 94.
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 94.5 will have the old style gear cut, and cases with a build date of post 94.5 will have the new style gear cut.
My personal experience is that a 249 with a build date of 3/94 still used the old style gear cut.
If you're swapping a 242, you can do what is referred to as a front case swap if you're in a bind with two different gear cuts (no pun intended.) The 242 and 249 both share the same front case half, meaning you use all the parts from the 242, with the exception of the 249 input, 249 planetary set, and 249 front case half.
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.
93-95 V8 ZJ's: 46RH transmission, 1.55" 23 spline input shaft
93-95 I6 ZJ's: Used both the .750" and .840" 23 spline input with the 42RE and AX15.
93 I6 ZJ's with the AW4: .750" 23 spline input
All 96-98 ZJ's: .840" 23 spline input
Drive shafts: While there are several different length drive shafts used though the years, the physical dimensions of the 231, 242, and 249 are very similar. The overall length of each case is within + or - 1/4" of each other, per slip yoke configuration. There are two different slip yoke styles used for the rear drive shaft: Internal and external slip yokes. They are easy to decipher from one another as, well, one has an internal shaft with a tail cone and the other has an external shaft with a dust boot. The external slip yoke is generally found in 96 or newer Jeeps while the internal slip yoke is found in older Jeeps. There is really no huge advantage to either style, however I like how the drive shaft splines are always submerged in ATF in the internal slip yoke case.
The biggest difference between the two is that the external slip yoke case is about 1.5" longer than an ISY case, meaning if you replace your ISY 249 with an ESY 242 for example, you will have to cut and balance your rear drive shaft or have the drive shaft from the donor Jeep on hand.
EDIT: Check out the link in my post above yours to see what vehicles possible have the same input shaft length, but off the top of my head I think in your case you HAVE to swap the input shaft