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This swap will require you to change the input gear on your transfer case. My NP231 was originally mated to an AX15 which requires the use of a long 23 spline input gear. (I believe that a TJ with the 3 speed auto also uses the long version.) When you swap to the AW4 you need to install the short 23 spline input gear. There is about a half an inch of difference between the two.
You have three options:
I chose to replace the input gear with a new one. Bob Bassett chose to cut his down. Any of the above choices will work. It's really up to you. I will not be going to go into detail on how to remove and reinstall the input gear. This information can be found in the factory service manual. Be sure to have a couple good sets of snap ring pliers handy. You will need them!
***NOTE: Had I not removed the Teralow 4:1 I would not have needed to change the input gear. All of the 23 spline Teralows are of the short variety.
***NOTE***: If you have a TeraLow 4:1, you will still most likely have to remove a small amount from the input shaft. Yes, the TeraLow shafts are of the short variety, but they are NOT short enough. For more info on this, see Stu's AW-4 swap write-up.
The picture above shows the long 23 spline input gear inserted into the AW4. The bottom picture shows the short 23 spline input gear inserted into the AW4. You can definitely see the difference. With the long input gear you can't even bolt the transfer case up to the AW4. Installing the short 23 spline input solves that problem.>