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Thread: T case first...discussion...

  1. #1
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    T case first...discussion...

    So... I am soooo thrilled to finally have a ZJ to build. Wanted one for years!

    First order of business is to get the crappy 249 tcase outta there.

    I've scored pretty good here. I got a wicked deal (thanks to "WAGGY") on a used NP231J. It's 23 spline and in really good condition. Could probably just power wash it, install the SYE and bolt it right in. All good, but I also got a really awesome deal (thanks to Edgar McNiven) on a NP231C-HD, probably from a Dodge (?). It's definately HD...it's got the six planetaries, and heavy 1 1/4" chain and gears. Nice!

    Most obvious visual differences are as follows:
    - HD front case half is different, mainly it has 5 bolt main...J model has six.
    - HD main shaft MIGHT be longer than J main shaft...but i think it just appears that way because the HD cone housing is shorter than the J.

    Both front output shafts are same measurements/spline counts, just different chain gears...and it appears as though everything else here is workable.

    I'm thinking I'll grab the Planetaries and heavy chain/gears and put them in the J cases to build my self a HD that will bolt up to my Grand.

    Will they fit? Anyone ever tried this? Any words of wisdom/experience from the tcase gurus out there? Any body see anything that I don't...?

    ...discuss...
    '94 Grand Cherokee Lerado
    7 inches up
    Long arms by STAANG
    NP231
    35" Mudkings
    yadayadayada...

  2. #2
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    Here's some pics:

    HD Front case...six planetaries and heavy chain gear on main shaft


    HD chain and Large out put gear


    Guess I can't use this case half


    This 231 came out of a Jeep


    Six bolt main...23 spline

  3. #3
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    Best of luck to you wish I had some insight for you but I will say this Ill be watching this build thread as I have a V8 ZJ with the full time 4 wheel drive T case and Id love to be able to select 2wd only so that I can save a little bit of gas

  4. #4
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    the upgrade has been done, I have read about it. I'll look around, I remember seeing it somewhere.
    I think a Google search for "231 upgrade" may help a bit. If I can find it I'll post back.
    insert something witty here

  5. #5
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    Yup...lot's of write up from Google search...but all are with a JB Conversions or Advanced Adaptors KIT. (This is a really good one)
    I'm thinking about using stock parts here. At this point I suspect that everything will work eventually...just gonna have to dive right into it and see what happens.

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    seems your right, it has been a while since I saw anything on it.
    as you said, your gonna need a few aftermarket pieces to make it work I guess.
    the MadXJ site
    has some good info and a good write up, that thread you put up is a great walk thru... wow.

    good luck with the upgrade.

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    I am unsure about the chain and gear swaps but the HD 6-planetary Input gear housing should fit no problem IF the 23-spline input has the same pitch as the Jeep transmission 23-spline output/Jeep 23-spline input (3-planetary).

    A friend of mine has done this and one 6-planetary 23-spline worked, the other one didn't... I am unsure of what vehicles the t-cases came from that the planetaries were used but my guess would be chevys. Also I believe they were both NP241 cases.

    Good luck

  8. #8
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    ^^Nice!^^
    thanks for the heads-up.

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