Long NP231 input gear on an AX15 transmission?

freedom_in_4low

freedom_in_4low

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There seems to be some room for uncertainty in the wording Novak uses in this guide:

https://www.novak-adapt.com/knowledge/np-nvg-input-gears/
Which is interesting because I definitely have an AX15 and a long input gear.

20200118_205553.jpg


In spite of this seeming problem:

20200118_215955.jpg


Anybody else seen this before? Did some AX15s have splines machined farther into the shaft to prevent this interference? There don't appear to be any markings on the splines of either shaft to suggest they are making hard contact and the mounting surfaces make contact without any hint of interference. That said, by tape measure the end of the splines must be close enough to each other that they only clear because of the chamfer in the inside of the input gear shaft.
 
AjRagno said:
That Novak guide is not reliable. From what I have found, a 1999 TJ with an AX15 required a long input gear.

Among other sources: https://www.stu-offroad.com/engine/aw4/tcase.htm
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OK wow, you're not kidding. I have 2 transfer cases and Novak is wrong on both. I broke my housing and got a case out of a 2000 XJ with Aw4, which Novak says should have a medium length, but it has a short. I swapped the input gears and had the whole case together before noticing "hey, I thought I was supposed to have the short gear?" and had to think through all my steps to convince myself I didn't pull the gears out and put them right back into the housings I'd pulled them out of.
 
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I had seen a Utube video that said if you have the long shaft but need the short shaft to cut (IIRC) 15/16 off the end, smooth out the rough bits and then you are good to go. Again, this was Utube.
 
Recently I pulled the factory NP231J from my 99 TJ with AX15 and also found it to have a long input shaft. Anyone have experience whether I can also run a NP231J or NP242J with the short input shaft behind this transmission or if I need the long shaft?
 
Yasha said:
Recently I pulled the factory NP231J from my 99 TJ with AX15 and also found it to have a long input shaft. Anyone have experience whether I can also run a NP231J or NP242J with the short input shaft behind this transmission or if I need the long shaft?
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There's a thread about it on here somewhere, but if I recall correctly, the short input will work on everything but the 32RH (and even that can work with a seal extender).
 
I reached out to Novak with my finding and we're not alone, though I'm told by Novak we should expect short length input gear on NP231 or NP242 to work with late model AX15 AKA the one we get in our TJs. I'm close to testing this in my garage, I'll do my best to remember to update here when done (rebuilding tcase with short input gear atm)
 
Yasha said:
I reached out to Novak with my finding and we're not alone, though I'm told by Novak we should expect short length input gear on NP231 or NP242 to work with late model AX15 AKA the one we get in our TJs. I'm close to testing this in my garage, I'll do my best to remember to update here when done (rebuilding tcase with short input gear atm)
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Somewhere around 1998 or 1999 they started shipping all of them auto or manual with the long input. It’s hard to track with the parts manual but every person I’ve seen post up from at least 1999 has had the long input.

I don’t think anything ever changed on the AX15 to make that work but I haven’t tried to use a long input on an older AX15. It is possible they cut the splines deeper at some point, I have no proof or info either way.
 
machoheadgames said:
Somewhere around 1998 or 1999 they started shipping all of them auto or manual with the long input. It’s hard to track with the parts manual but every person I’ve seen post up from at least 1999 has had the long input.

I don’t think anything ever changed on the AX15 to make that work but I haven’t tried to use a long input on an older AX15. It is possible they cut the splines deeper at some point, I have no proof or info either way.
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My understanding was that it was all long input until the 42RLE, and then it was all short. Which means AX15 and 32RH always paired with long, 42RLE and NSG370 always paired with short, and the NV3550 bridged the transition and could be found with both. Though I haven't personally touched a 98 or earlier AX15 to know for sure that they never had a short input.

I don't mess with automatics but my long input 231 has been mounted to two different AX15's, including one original '99 and an Aisin/Novak replacement from 2022, and has also been mounted to an NSG370 which only ever had a short input, but it had about 1/8" to spare before the input would have run into the trans output seal.
 
freedom_in_4low said:
My understanding was that it was all long input until the 42RLE, and then it was all short. Which means AX15 and 32RH always paired with long, 42RLE and NSG370 always paired with short, and the NV3550 bridged the transition and could be found with both. Though I haven't personally touched a 98 or earlier AX15 to know for sure that they never had a short input.

I don't mess with automatics but my long input 231 has been mounted to two different AX15's, including one original '99 and an Aisin/Novak replacement from 2022, and has also been mounted to an NSG370 which only ever had a short input, but it had about 1/8" to spare before the input would have run into the trans output seal.
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Earlier years like the YJ and the 97 TJ were short for sure on the AX, and long on the 32RH. My 94 had a short as did several others I've seen. Jerry's 97 with the AX15 had the short, I recall for sure he needed the extended seal when he did his 32RH swap. Every 99 I've seen someone post about was long, so at some point Jeep had to have said "why are we still shipping both?" and consolidated down to the one that worked for each. I highly doubt they had any changes made to the transmission, but it's possible.
 
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Yasha said:
I reached out to Novak with my finding and we're not alone, though I'm told by Novak we should expect short length input gear on NP231 or NP242 to work with late model AX15 AKA the one we get in our TJs. I'm close to testing this in my garage, I'll do my best to remember to update here when done (rebuilding tcase with short input gear atm)
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I don't see any reason why a short input wouldn't work. I think Jeep truly had the light bulb go off and realized they could consolidate the parts they were using. You can see in the pics in the beginning of the thread that the transmission seal is still riding close to the transfer case.
 
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machoheadgames said:
I don't see any reason why a short input wouldn't work. I think Jeep truly had the light bulb go off and realized they could consolidate the parts they were using. You can see in the pics in the beginning of the thread that the transmission seal is still riding close to the transfer case.
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Ditto from me as well now. Short length input shaft of NP231 does indeed still mate with the transmission seal.
 
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