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Unread 02-28-2011, 04:43 PM   #1
HOOT-1987YJ
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NP 231 - rear output spline count with SYE

Does it matter what the rear spline count is if I purchase a SYE? I'd like to order the SYE before I take out the case. PO said it was 23 but I don't want to just go on his word. I tried some different searches but couldn't find much talk about rear outputs. Thanks!
Hoot

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Unread 02-28-2011, 07:03 PM   #2
moonshinefuel
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When you order an sye from any company, they will ask you the make of vehicle, year, engine, and transmission. That will determine what exactly they send you from the supplier to work with what you currently have. If the original components have been changed from the original factory ones, then you need to find out. Is it the original t-case? If yes, then you are good to go without needing to delve into this any further. Simply just order it, and they will send you the the proper sye for your year and config.
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Unread 02-28-2011, 07:19 PM   #3
HOOT-1987YJ
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Thanks Moonshinefuel! So I just give them all the info from the tag on the back and that should take care of it I guess. I believe it's the original case but I'm not positive. 2 owners previous to me put in a SBC 350 and TH350 with Advance Adapter to transfer case... so there's a possibility he changed the case too. It's an NP 231 AMC (not J) so I'm not sure if that is pre-YJ or what? I believe the 231J 4 cyl is 21 spline and the 6 cyl is 23 spline from my research, but not sure where an AMC came from. Any idea? It would be nice to know for future reference. Thanks!
Hoot
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Unread 02-28-2011, 07:57 PM   #4
Mean Max
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I think you're confusing input & output shafts. An SYE kit comes with a new output shaft, and will work with either a 21 or 23 spine input shaft model NP231 transfer case.

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Unread 02-28-2011, 08:36 PM   #5
moonshinefuel
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Oh ok, well yea that sounds like an earlier t-case yes. So they did that because the original 21 spline t-case would not have worked with the installed drivetrain unless they changed out the shaft. They found a good 231AMC and went with that, that's good. Yes, give all the info off that t-case tag to them, and that should be enough, is there a year stamped onto the tag as well?
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Unread 02-28-2011, 09:26 PM   #6
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One of the things you will be looking at with the supplier of the sye is that the speedometer works with your new sye you will be installing with the t-case you have in it. Its possible the mechanical gearing has never changed from the inception of the 231 up right until the electronic speedometer version. MeanMax may be able to shed some more light on that.
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Unread 03-01-2011, 04:11 AM   #7
HOOT-1987YJ
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Mean Max - thanks for the answer. I'll just order it then. I could not get my head around how the input shaft and rear output shaft connect. So I was thinking they had to match spline wise or something. I've never seen the inside of a Tcase.
Moonshinefuel - I do not believe there is a year on the case. Not sure of the speedo either so I'll need to figure that out.
Maybe the NP231 AMC came out of an old CJ that had an AMC 360. Makes sense in my mind anyway. Maybe it's more HD to match up with the current 350. Hope so anyway.
THANKS!
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