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Discussion Starter #1
I am in the middle of my 350 swap and i was using a Np231C to save money over buying the adapter from AAdapter ($481) for the NP231J, the speedo setup on the tail cone is different, is there anyway around this? jeep uses a mechanical gear to read speed, the chevy a sensor, i need to get this back on the road asap this is really the only thing hanging this up from being done this weekend/next weekend are the output shafts swappable? i dont have a SYE due to riding stock still, my NP231 is the 4 cyl jeep version. :confused: Any help apreciated, thanks
 

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I've seen a post on this site about upgrading to the wider chevy chain and associated sprockets in a jeep 231. I think it was bolt in. If it were me I'd just try to swap out the tailhousing and tailshaft and see if it will work. Maybe you'll be the pioneer (or the guniea pig).
 

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Discussion Starter #3
me being a guniea pig is scary... do you know if the input shaft is separate from the ouput shaft... it is possible for me if this is the case, otherwise i would have to obtain another input from a jeep... the chevy is wider.. that i didn't know... i may end up attaching a bicyle wheel outside the drivers door for a speedo :D
is there info -- prefer with pics... how to tear it down someoplace?
 

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88 s-10 np231c

I just completed a 350/TH350 swap in my parents 89 wrangler. I too used the np231c. In order to use the mechanical speedo you need to use the np231c out of an 88 s-10. This was the first year of the np231c, and all years after (89-up) used the speedometer sensor which you have. Hope this helps!!!

Derek
 

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Discussion Starter #5 (Edited)
Re: 88 s-10 np231c

95blazer said:
I just completed a 350/TH350 swap in my parents 89 wrangler. I too used the np231c. In order to use the mechanical speedo you need to use the np231c out of an 88 s-10. This was the first year of the np231c, and all years after (89-up) used the speedometer sensor which you have. Hope this helps!!!

Derek
if i didnt have a 91 231c it would help... now i have to get it converted or something, can i buy an output shaft for an 88 and stick it in the 91?... mine (the s-10) isnt a mechanical speedo, its just a mechanical sensor... would an aftermarket speedo guage work? or would i have to have a cpu and stuff from a s-10 to run the speedo. i have the s-10 sensor and a piece of the pigtail, but thats it.
 

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Discussion Starter #7
Jason R said:
Think twice before putting a 231 behind a 350. :nuke:
i have thought about it quite a bit... this is what i chose after 2 years of research, and a 2.5 puking unexpectedly, if i could afford driveshafts and everything else right now i would do something different, but i cannot, esp when its a daily driver out of commission. the NP231 will hold up fine for what i do with my jeep and have friends running the same setup, im not worried about it, especially when the 350 will be stock other then intake, carb, and headers, and if it grenades there is another at the JY for 100 bux easily found.
 

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I dont know if it will work but I have heard of using the front case half from the chevy and bolt it to the rear half from the Jeep.

Yes the input (and planetary)is separate from the output shaft and chain.

I have always wondered if this will work,let me know if this works or why it wont.
 

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Discussion Starter #9
if they are seaprate i assumed so or you wouldnt have 4hi and 4 low (which is the key piece of information i needed before tearing it apart) this is VERY likely possible due to the fact that the casting #'s are identical for the back panels, i also took measurements and they are the same for the rear panel, i will keep you informed, i will be tearing it apart later this week, if not sooner. the only snag i would see here is if the chains are indeed 2 different widths... and i am going to pray on this one...
 

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I am pretty sure that a 231 chain is a 231 chain. The wider chain used to upgrade a 231 is actually 241 chain.( I think)
 

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Discussion Starter #11
ok well then i'll definitly be taking a looksie ... i had thought that same thing, but it was mentioned above about the wider chevy chain and that confused me, because i thought with the tail cone off they looked the same width.
 

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The "wider" chain is only 1/4" wider. The 241 chain is 1.25" and the 231 chain is 1". The way I understand it you can actually use the wider chain in a 231 case with no case mods. Also, I'd be interested in knowing the planetary set up in the 231c. Is it 3 gear or 6 gear? I feel confident you can change out the output housing and talishaft and be okay. If you search for SYE's for the NP231j most of them say they will work with the NP231d and NP231c if you are switching to the Jeep speedo drive. Be sure and post the results. Pics too if you can.
 

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Recurve said:
The way I understand it you can actually use the wider chain in a 231 case with no case mods.
Yes, this is a common swap for some reason.
I beleive it is JB Conversions that sells a kit to do this swap.
And you should be able to install a SYE kit with a heavy duty output shaft to gain your needed mechanical gear speedo.
 

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YES, IT WILL WORK.

Just put your Jeep output shaft in the Chevy transfer case and you're done. I did this with mine, pulled my SYE out of the Jeep transfer case and put it in the S-10 transfer case. The only difference (besides the chain width) is the speedo drive. Use your Jeep shaft and be done with it.

On another note, it will hold up behind the SB Chevy. I've been running mine for three years with 35's, 38's, and now 39.5's. I did, however, pick up a spare for $50.
 
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