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Thread: NP231 Transfer Case Upgrade to 6-Planetary Gear

  1. #1
    Rock Crawlers mAdMan's Avatar
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    NP231 Transfer Case Upgrade to 6-Planetary Gear

    Taken from www.madxj.com a sweet xj tech site. not a club. images held there

    This is a summary of what I did to beef my Jeep 231 transfer case.
    First, I installed a 6 pinion planetary set from a Chevy NVG241 transfer case in place of the Jeep 3 pinion planetary set. Next, I found a set of 231 chain sprockets that were about 1/4" wider than stock. I believe they came from a NP207 although some non Jeep 231's also came with them. I couldn't come up with a good used wide chain, so I purchased a new one through the recycling place where I came up with the other parts. It was around $75.
    Finally, I added these parts to an Advanced Adapters Heavy Duty Slip Yoke Eliminator kit.
    I had two Jeep transfer cases at my disposal, so I mixed and matched different components so that one was built with the better parts and one was built with the stock parts. I had to use the '93 case for the HD unit because the six pinion planetary that I purchased had a matching gear cut to the gear in the '93 case.
    Somewhere between '93 and '98, the gear cut changed, so the six pinion planetary I had procured would not mesh correctly with the gear in the '98 case.
    I did use the '98 low range shift fork in the HD case as it appeared to be built a bit heavier than the '93 unit. I did however stick with the '93 mode fork in the HD case as its pin that rides on the shift cam has a roller where the '98 unit was a solid pin. I had a Currie SYE installed in the '93 case, so I reinstalled that in the '98 case.
    Warnings!


    Familiarity with transfer cases is highly recommended before proceeding with this modification!
    Generally accepted shop safety rules apply!

    The Parts


    NP241 6 pinion planetary to match the gear cut in case
    '98 low range shift fork (beefier than the '93)
    1.25" wide front output shaft/sprocket (upgrade from 1" wide stock)
    1.25" wide chain to match sprockets
    '98 oil pump (it had less miles on it)
    Advance Adapters HD slip yoke eliminator kit (larger output)
    Rebuild kit (new bearings and seals throughout)
    Thread locker
    Silicone to seal the case halves together

    The Tools


    A good snap ring pliers (flat blades opening upon squeezing the handles) is the most important
    A puller is perhaps useful
    A 1 1/16 socket for the yoke nuts is needed
    A Torque wrench is supposed to be used
    A 30mm socket fits the '93 fill and drain plugs
    I would say a FSM is a good thing to have
    A press may be useful for bearings and such
    The Procedure


    ALL PICS HELD AT WWW.MADXJ.COM UNDER TECH WRITEUPS


    Summary


    I got most of the needed parts from salvage yards. For $50 I got the six pinion planetary from a box of 241 parts and (on the second try) a set of 1.25" wide sprockets that matched the stock stuff in all other regards from a box of 231/233/207 parts.
    The first time at the yard, I picked up a set of wide 241 sprockets and a chain, but they were WAY wrong once I got my case apart and compared things. I couldn't locate a wide chain for a 231/233/207 case at that yard, but they said they could get me a NEW wide chain for $75 and have it drop shipped to my house, so I did that.
    A different option for finding the needed parts was to purchase a core from a core buyer over by Minneapolis. He said he could sell me a core with the parts I needed for $75, but I don't get over there very often and with the parts I did find, the cost would have been pretty much the same.
    I later found out that Dakota NP231D's actually use a larger synchronizer and shift ring in addition to the wider chain and sprockets, but since the 241s use the same synchronizer and shift ring as the stock NP231J cases used in Jeeps I figured that would be strong enough.
    The AA SYE was $210 shipped from MAD4WD, and I purchased a NP231 rebuild kit for $75 from National Drivetrain on sale.
    I was not real impressed with the rebuild kit, but it did have the input bearing which I was having a hard time sourcing locally. The front output seal in the kit was NOT a double lip seal. Also, a couple of the bearings were foreign although the stock ones were too.
    So, I sunk $410 into this case plus misc. stuff like paper towels, brake cleaner etc.
    Not bad for a case that JB Conversions sells for $925, but still not cheap.

    BTW, at 165,000 miles, my stock chain matched the new one for length with one set on top of the other one.

    Here are some other useful links: Novak has good information on the input gears which can be found at:
    http://www.novak-adapt.com/catalog/model_231_parts.htm

    Just for inf., here’s a reference to a NEW ultra short SYE:
    http://www.novak-adapt.com/catalog/kit_231sye.htm
    Too cool!

    I think it was jeeptheplanet who was having np231 problems...might want to look into this!

  2. #2
    Wheelers xjtim's Avatar
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    Good stuff...good lookin out Adam!
    I'm all jacked up on mt dew!

  3. #3
    Rock Crawlers XJPRIDE13's Avatar
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    This sounds cool to do
    Would this make it stronger
    What are tue advantages of doing this compared to a doubler
    XJ FOR LIFE

  4. #4
    Rock Crawlers mAdMan's Avatar
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    i believe a doubler would give you two or more low ranges. but you will need front and rear driveshafts and a new crossmember plus larger skid plus a new exhaust plus a LOT more fabbing.

    this is bolt on
    Only one low with a stock 231. this mod would definately make your np231 beefier. Much wider chain and 6 planetary gears from a chevy vs. only 3 in ours.

    Be like upgrading to a d44 from a d35

  5. #5
    Rock Crawlers XJPRIDE13's Avatar
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    i see :)
    shit if i had the know how to do this i totally would seems fun and useful for sure
    XJ FOR LIFE

  6. #6
    Wheelers jeepirate's Avatar
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    yeah i have had this site on my favorites list since the begining , it has tons of cool tech stuff
    JEEPIN' AIN'T EASY

  7. #7
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    Looks pretty cool.
    Owning a Jeep is about the freedom and capability of overcoming obstacles that a multitude of other vehicles cannot surpass.

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