I tried digging through the parts catalogs from 97-99 TJ and XJs but they were ultimately not very helpful.
Some basics:
- All 90s and later AW4, all AX15, and all 30RH/32RH are 23-spline outputs.
- AX15 only required a short t-case input gear, but medium or long could be used
- 30RH/32RH required a long t-case input gear, or an extended seal from Teraflex or similar.
- Not sure what AW4 had, but it seems to be either short or medium from photos.
I know for sure that in the YJ days, and early TJ days (1997ish), they used a short input for manuals and long input on 3 speed autos. Somewhere in there, they started shipping all the TJ NP231s from 1998-99ish and onward with the long input, whether it was going behind the auto or manual. The manual was fine with the longer input, it just didn't require it for sealing purposes.
The parts catalog doesn't really help with any of this. The TJ 97-99 catalog lists one part number, 4796965, and calls it out for ER0 (4.0L) and EP0 (2.5L) with automatic transmission. The XJ parts catalog calls out that same part number as being for Magnum 2.5L SMPI with all automatic transmissions. So I honestly don't know there.
If you are needing to build a t-case to go behind a 30 or 32RH, use a long input gear. If it goes behind an AW4, you'll need to research more what goes behind them. I can't find too much for-sure info on that, BUT it does seem like they used a short based on eBay photos. So look more into that. If it is going into an AX15 or NV3550, a short will work, long can also work on the AX15, not sure on the NV.
I can't think of any other differences that would exist in the t-case. They were setup for the same drivetrain characteristics by the late 90s, so they both have no synchronizer, no vacuum CAD, etc. When you get to the older cases like 92 XJ and earlier, then they start to have the CAD switch, synchronizers, cable speedometer gear setups, etc. By the late 90s they were pretty much figured out and no longer changing things.
FYI, if you need to buy an input gear to make something work for your needs, pay attention to the gear cut and bearing width. Early-cut models were a more squared tooth tip and they had the wide bearing. They went til about the end of 1994. You do not want that for any of your late-90s cases. Late-cut were a more rounded tooth into a sharp tip, and they had the narrow bearing. So make sure you look for the late/narrow bearing keywords to choose the right input gear for your needs, if you have to buy one.
