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.
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.
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.
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.
