Transfer case swap to 4x4 - 231C vs 233C

Transfer case swap to 4x4 - 231C vs 233C

Postby zGerman [OP] » August 30th 2019, 6:47pm

My current NP136 transfer case does not play nice. Instead of taking it apart to fix it I consider evicting it and get a 4x4 case with 4H and 4L and a manual shift option using a lever. In a separate thread I posted Mmusicman mentioned that both the 231C and 233C Tcases work but the internals may or may not be beefier in one vs the other. My 2001 AWD is running the stock 4.2 engine, stock automatic transmission + tow option and 30 inch tires that may grow to 31 inch down the road. I broke a lot of 4x4 parts in my life but not any T cases due to stress. So my questions are....

Do those cases have internals that are significantly stronger in one vs the other?
Do I really care since my available power is stock applied via the automatic transmission to reasonably sized tires?
Does either have a known issues like maintenance difficulties, leaks or wear parts I should know of?

If the setup described above can't break a NP231C and all is more or less equal between those I probably go that route as it was designed to be shifted with a lever. It has the proper detents between the shifting positions. It also allegedly requires less shifting force but I am not too worried about that difference. I live in Las Vegas so I don't have too many snow days in the city but can use 4x4 support at least twice a week on gravel, rocky roads or dry washes outside the city limit. Having 4L would be great. I like to use it just to slow down if desired even if I don't need twice the torque. Bye bye AWD, hello 4x4!
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby CopperFiremistCopperFiremist is online! » August 30th 2019, 10:56pm

Well I've got over 20,000 miles on my 233 with countless V8 burnouts and its still hanging in there. Quite a few posts on here about swapping Tcases. Mmusicman has great write up on it.
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby zzimmer3 » August 30th 2019, 11:11pm

My 233 has been trouble free for many miles. Highly recommend!
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby Mmusicman » August 31st 2019, 3:16pm

After re-reading Gavio's thread, it would appear the 231-C has the same wider heavy-duty chain as the 233-C. It seems the only disadvantage I can see of the 231-C might be the work needed in assimilating the "factory shifter" (which you don't actually have to use). I suppose my "side of seat shifter" design could have just as easily been incorporated. The only other drawbacks of the 231-C may be getting simply locating one? (uncertain about parts)

In either case of both the 231C or 233C.. you will need to fabricate something for a shifter.. whether using the factor shifter, or making your own. The Liberty shifter is also still a great option, but would also need some form of modification to completely fit.

As far as using the 233.. it really isn't hard at all to drill and tap the shaft (actually very easy), and fabricate a piece of bar-stock into a shifter arm. A standard shifter cable did the rest. In my case I feel it was far less work that trying to in corporate the factory 231 shifter. I also didn't like the idea of losing valuable floor space... but to each his own. The floor shifter certainly "looks cool"... :D (but I think my seat shifter looks pretty cool too)

But you can't go wrong either way!!!
I highly recommend the upgrade!!!

Mine is SO awesome... tucked away inconspicuously with the shifter arm mounted to the side of my seat.. you never know it's there until you need it and reach down for it! Couldn't be ANY better IMO! Seriously! I don't have any kind of "indicator".. but you can't NOT know you are in 4x4 mode when you pull the lever, or which distinct position you are in.

Looking forward to your upgrade mod and photos!
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby WinnieVan » August 31st 2019, 7:14pm

231 and 233 are the exact same internals... seems the 231C usually has the 1.25" chain and the 233 might have a 1" chain... but there are plenty of 233s with 1.25" inch chains.

The other things that could differ are the number of planetary pinion gears -- but again, New Process pretty much just used what they have laying around -- so I think you could find a 231 or 233 with either 3, 4 or 6 pinon planetary.

I think the 231HD comes with a 1.25" chain and a 6 pinion planetary -- but I think only Dodge used this transfer case, so you'd have to swap output and input shafts to make it work with a Chevy -- which is more trouble than it is worth, especially since you can buy a 6 gear planetary on eBay if you really want to.

So -- as others said and you previously knew -- the NP231 is pretty much identical to the NP233 -- save for the shifting mechanism.

I think the NP231 is easier if you want to stay with manual shift -- even if you end up building your own linkage.

I think the Jeep Liberty shifter is best way to control the NP231, but you'll need to figure something out for mounting the TC-side of the cable shifter.

Also check out this Hotwire thread on replacing the vacuum switch with a electronic switch to tell your PCM you are in 4LO:
https://www.astrosafari.com/viewtopic.p ... 0#p1026002

I honestly thought that mod was too crazy for me -- but I tore down my TC to check it out and it is *really* straight forward.
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby zGerman [OP] » September 1st 2019, 10:23pm

Great info - thanks. I will start sourcing parts and get going. I like the JOR bracket to keep the shifter arm in place, I could cut one like it relatively quickly. I initially assumed that any shaft in a T-case is about as hard as my cheap drill bits so to drill and tap seemed like a real project. I am glad to read that it isn't actually difficult to drill and tap the shaft. Depending on the shifter design I end up using I may go the route Hotwire described and knock of the corner from the "cam" thing and use the switch he sourced. Seems a like very clean install even so I am a bit worried if folks say "just trim it" and to get the part out takes half a day to perform a 30 second cut. That is still an unknown to me, maybe with the case on the bench I can get it done in 30 minutes? Alternately if I find a Liberty like shifter with a switch attached I may just replace the T-case vacuum switch with a short bolt and a copper washer to seal it for good.
VSS - what options do I have to make the speedo show the actual speed? In a Dana 300 one can switch the plastic speedo gear and if your math is right the result is pretty accurate. Any such option on a 231/233 or are there any computer options to make the speedo show true?

So many options, I leave the complete solution open depending on what parts I find cheaply.
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby zGerman [OP] » September 4th 2019, 2:57am

I found all needed parts online. The transfer case will be a NP 231C from car-parts.com costing $133 with tax shipped to Vegas. The shifter is from a Liberty and cost me $75 from ebay with the shifting cable. Since the shifter has the electrical part build-in to get the computer informed about the 4x4 low range I only need to fab some bracket for the shifter cable and do other minor stuff. The shifter even comes with the leather like boot intact. All should arrive within a week. I may delay the actual install until temperatures drop to say 95 outside. My van has a extended roof so it doesn't fit inside my garage.
Thank you for all the info in your replies and the posts on here, without this forum I would have not tried any of this!
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby Mmusicman » September 4th 2019, 2:24pm

zGerman wrote:I found all needed parts online. The transfer case will be a NP 231C from car-parts.com

FANTASTIC!!! The day your TC arrives... you take your first photo taking it out of the box AND start your build thread!

Thank you for all the info in your replies and the posts on here, without this forum I would have not tried any of this!

I'm with you on this one! I would have never even suspected I could swap out my TC from AWD to 4x4 without this forum. :D

Enjoy!
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby Captn.Crunch » September 4th 2019, 3:33pm

Both mods have proven durable and doable with only minimal fabrication required. Here in the Northeast I have opted to retain my AWD and so used the 236. Life is good with a 4x4 van!
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby Mmusicman » September 4th 2019, 7:09pm

Captn.Crunch wrote:Here in the Northeast I have opted to retain my AWD and so used the 236.

Best of BOTH worlds.. the ULTIMATE AWD/4x4 setup!
Life is good with a 4x4 van!

Yes it is!!! I've always dreamed of having a 4x4 van.. had no idea how close I was when I got the AWD.
It doesn't snow enough here in South Florida.. so I have no need for AWD.
But if it did.. I would have considered the 236.
I did however have a STRONG need for 4-low.. which has worked perfectly for me when the time finally came!
I can still use my manual TC in the rain & snow if need be too. :D

The direct bolt-on ability (and availability) of the 231/233 made mine an easy choice!
The only uncertainty of ALL of them is how you device your shifter.
But still easy enough!
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Re: Transfer case swap to 4x4 - 231C vs 233C

Postby Rinny » September 6th 2019, 9:32pm

I believe Journey's off road now has a kit
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