231J HD build for 21 spline question

Goose_XJ88 · Nov 8, 2013

Alright guys, Im starting to do some research on building a HD 231J. The problem that I'm running into is that all of the build threads that I have read are for tcases out of HO, 23 spline jeeps. The other part that I'm not sure about is a few builds have mentioned using portions of the 241d, 231c, or 231dHD like the input or output shafts that mention they are larger (32 spline) than even the 23 spline 231J. I'm wanting to do the 6 gear planetary and the wide chain conversion.

These are the threads that I have read up on.

http://www.cherokeeforum.com/f67/building-231hd-t-case-126689/
http://www.greatlakes4x4.com/showthread.php?t=208056
http://www.fourwheeler.com/how-to/1005or-np231j-transfer-case-upgrade/

I know its a WJ, but has some same info

http://www.jeepforum.com/forum/f310/231hd-build-1291209/
http://www.jeepsunlimited.com/forums/showthread.php?546606-231HD-build

Goose_XJ88 · Nov 18, 2013

Has anyone done this type of upgrade to a renix era 231?

If possible, I want to pull all of these pieces from a junk yard at one time and piece it together in the yard so that I don't have to pay for the parts separately. I cant afford to spend an entire day dropping and piecing together three transfer cases, especially if it isn't going to work.

MoparManiac · Nov 18, 2013

Do you NEED the vacuum disco capability that the renix era 231s provide?

If not, I would just go with a NP241 from a Dodge/Chevy (make sure it's driver's side drop obviously) and get the benefits of a beefier case, 32 spline outputs front/rear, and you can even drop in your 21 spline input shaft to the 6 pinion planetary set.

Very easy to do the internal stuff, but not sure how the clocking lines up on them.

Goose_XJ88 · Nov 18, 2013

no I dont need the disco but i have a 242 in my jeep currently. I didnt know if the 242 input shaft would be the same as the 231/ 241dHD. That was the other unknown; I hadnt seen any threads where the 21 spline was used so I was unsure if the planetary gear pitch was the same between the 21 and 23 spline shafts. Im not that hard on my jeep so I dont think I absolutely need the beefier 241 case but if its easy, I will do it. I also want to keep my stock interior and have a JCR 231 TC skid I want to use.

With using the larger spline outputs of the 241, Is there a yoke from another vehicle that I need to grab or do the two vehicles use the same u-joints? Also is the rear of the 241dHD a slip or fixed yoke? I dont want to buy custom driveshafts that use different u-joints on each end.

Basically I am wanting to switch out my 242 from my 88 for the stronger, 231 transfer case and figured I might as well do the HD mods while doing the swap. I like the idea of even more beef with the 241, but not if its going to cost me an arm and a leg to get it to work right.

Current specs:
88 XJ w/ 6.5" lift on 33s
242 w/ H&T
non-disco d30/d44 w/ 4.56

MoparManiac · Nov 18, 2013

A 241 from the earlier years should work. I don't know all the specifics but I believe pre-94 should work for you.

The case itself is much bigger. Look through my build thread (link in my sig) as I used a 241 for my doubler setup and show comparisons next to a 231.

The rear is a slip yoke. Not sure if you can just use a 231 SYE for it, I never researched it.

You won't hurt a 231 even without the HD mods. I ran one for 2 years on D44s and 35s. I wouldn't worry about a 231, was just throwing out the 241 option if you really wanted the HD beef.

emptypockets86 · Nov 22, 2013

ae racer said:
no I dont need the disco but i have a 242 in my jeep currently. I didnt know if the 242 input shaft would be the same as the 231/ 241dHD. That was the other unknown; I hadnt seen any threads where the 21 spline was used so I was unsure if the planetary gear pitch was the same between the 21 and 23 spline shafts. Im not that hard on my jeep so I dont think I absolutely need the beefier 241 case but if its easy, I will do it. I also want to keep my stock interior and have a JCR 231 TC skid I want to use.

With using the larger spline outputs of the 241, Is there a yoke from another vehicle that I need to grab or do the two vehicles use the same u-joints? Also is the rear of the 241dHD a slip or fixed yoke? I dont want to buy custom driveshafts that use different u-joints on each end.

Basically I am wanting to switch out my 242 from my 88 for the stronger, 231 transfer case and figured I might as well do the HD mods while doing the swap. I like the idea of even more beef with the 241, but not if its going to cost me an arm and a leg to get it to work right.

Current specs:
88 XJ w/ 6.5" lift on 33s
242 w/ H&T
non-disco d30/d44 w/ 4.56

The pitch of the input is the same, it doesn't matter if its 21, 23, 27 etc. There are two different gear cuts though based on year, early and late gear cut. 94 is the cutoff year for the early gear cut. You can tell the difference based on the bearing size for the input gear, thin is late and wide is early.

This is an early gear setup:

I'm on the app and can't go back to your post, but are you just upgrading your planetary and adding a sye or are you also doing the wide chain upgrade?

Goose_XJ88 · Nov 24, 2013

I'm wanting to do the planetary and wide chain. I figure I might as well do both since the 231 will be "new to me" and I'll already have it apart. Ill also be doing a sye, just havnt decided on full or h&t since my current 242 h&t hasnt failed me yet..but with the upgrades Im already planning, I might as well go with the beef of a full SYE..

Then again, based off what MoparManiac said, I may just throw a stock 231 under my rig considering Im really not hard on it.

231J HD build for 21 spline question

Goose_XJ88

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Goose_XJ88

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MoparManiac

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Goose_XJ88

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MoparManiac

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emptypockets86

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Goose_XJ88

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