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Thread: Transmission swap

  1. #1
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    Icon91 Transmission swap

    I have a 74 CJ5 with 258, T150, model 20 w/Tera Low, Even with the Tera Low the three speed is too fast in the rocks. Been looking for a T18A but no luck. what are your thoughts on the NP435? Advance adapters says I need their adapter kit but it's $517! Any other options?
    I found an NP435 rebuilt for $150 but I'm wondering what other hidden expenses I might have? Drive shafts need legnth change? clutch? Transmission mount?
    Any other suggestions?
    Thanks

  2. #2

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    Don't have any specifics for you, but I seem to recall folks having issues with pilot bushings that they had to sort out to finally get everything in place. Might try some searching here and on cjoffroad.com I know one of my buddies posted some of his trials & tribulations over there as he went back & forth with Novak to finally get it together. I know he was very pleased with the setup once it was finally together.
    '00 XJ (the kid is driving now)
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    '83 Scrambler: full-caged,locked Dana 44/60'd,36" Swampered,360/999/203/300 powered beast/time & money pit under construction with parts from CJ's,YJ's,TJ's,FSJ's,GM,Ford,IH,Honda,Toyota and a whole lotta aftermarket & custom stuff.
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    Why not an SM465? More common, made up until around '91, so parts are still quite availible. The only way to get around the adapters is to either use the transfer case that is behind which ever trans you are using, which is probably going to ad some more length. You will also need the correct bellhousing/adapter. I went with the Advance Adapter adapter for the 465 to 300, about $500 shipped. If you want to play, you gotta pay.
    .



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    5.7 tbi, sm465, d-300, M20, D30.

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    I've just been doing a lot of reading on old threads and wondering if I am on the wrong track?
    I still have the stock gearing in my axles. 30 front 44 rear. Should I be considering re-gearing instead of a transmission change?
    The Jeep is not a daily driver but also not a trailer queen. Most of the trails I ride are within an hour of home and I never run over 50-55 so lower gears would not be an issue.
    BTW-I am running 35/12.50's
    Thoughts?

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    Depends on if the stock gearing is 3.73 or 4.27. Both were available in '74. Find one of the many crawl ratio calculators available online and plug in the gear differences with a transmission swap and keeping the diff gearing compared to keeping the transmission and changing the diff gearing to make a decision. You'll find that changing from an approx. 3:1 first gear to a 6+:1 first gear makes a bigger difference to overall crawling than a gear change. The question is if it makes sense to your wallet or not.

    You sure of your drivetrain? The T150 didn't come around until '76. The stock three speed would have been the T14.

    The difference it makes is parts required. The T150 would use the same clutch as the NP435. The T14 would not.

    You will be looking at new driveshafts regardless of any transmission change.

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    You are exactly right...I had a t-14 but when I put the Tera Low kit in the tera had six spline gears and the T-14 had 10 spline output shaft so I swapped in the T-150. Wish I had had more time to investigate, I would have done the four speed then.
    My gears are 3.73's but I hesitate to spend the money to have someone change the gears in a dana 30 with locker on 35's. I'm guessing I'm on borrowed time there.
    So, it looks like the transmission swap is going to be the least expensive if I really want to go slower!

  7. #7
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    Actually, LEAST expensive will be going to a smaller tire, but nobody ever asks about that!

    Finding a tranny that has been adapted will be your next choice, that will take quite a bit of patience. NP 435/SM465 are both good trannys.
    Time owned by new house

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    Registered HackFabrication's Avatar
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    FWIW: I would go with either the Ford 2wd T18 or the NP435 and pony up the $$$ for the adapter. You MAW (might as well), replace the clutch and get the flywheel resurfaced when you pull everything. The driveshafts will need to be modified, but the trans will bolt to the existing bellhousing. 'Possibly' some skidplate/crossmember mods too.

    Another option would be to locate either the Jeep T18/D20 combo or the IH T18/D300 combo. However (IMO) both can be a bit 'overpriced', depending on your location.

    Here's the best gear calculator I've found: http://www.grimmjeeper.com/gears.html
    "In the end...It's all Hack."

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    If you have a bellhousing for a T150 then the Ford T18 may be a good option; no bellhousing to change but you do need a special pilot bushing and a rear adaptor. The bad news is AA list the rear adaptor as a $476 kit plus the cost of the tranny.

    Take a look at this link-

    http://www.jeeptech.com/convtrans/fordt18/

    Good Luck


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    Thanks for all the advice. I'm going to look for a good tranny and pony up the bucks for the adapter. If I didn't have the $800 Tera Low kit in the 20 I would just look for a tranny/transfer case combo but if I can get a granny gear 4 speed with the Tera Low I'm thinking I will really be able to crawl. I'm leaning toward the NP 435 because it's lighter than the other two and an inch shorter than the T18. It also won't hang down as far as the NP465.
    I am going to replace the clutch, it has chattered ever since Big Dogs last fall. Any advice on a heavy duty clutch? I put a cheap one in only a couple thousand miles ago

  11. #11
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    The NP435 transmission itself is shorter, but overall transmission/adapter length for the NP435 is longer than the T18/adapter overall length by a couple of inches.

    The weight isn't enough to worry about. It's down low where you want weight anyhow.

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    Thanks, I didn't realize the T18 with adapter would be shorter. I guess I'm back to looking for a T18. Seems like they are just really hard to find but once I do I'm sure it will be worthwhile.

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    Icon91

    My son has a NP435 in his "built" 401 powered CJ-5 and that 1st gear is SWEET.
    Has stock D/20 t-case w/3:54 r&p and d/l's fr & re. Go with the NP435, once it's up and running you will NEVER be sorry.
    The NP435 is a VERY heavy duty truck tranny. It will outlast us ALL
    Advance Adapters can/will ans. all of your conversion question for you.
    Best of luck on what ever you choose.
    Respectfully,
    LG

  14. #14
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    Quote Originally Posted by GweenJeep74 View Post
    Thanks, I didn't realize the T18 with adapter would be shorter. I guess I'm back to looking for a T18. Seems like they are just really hard to find but once I do I'm sure it will be worthwhile.
    in my experience, you just have to be patient and keep your eyes open. when I need one, I look for Ford trucks with 4 speeds. before things tanked, I could get a truck for $600, pull the tranny, and scrap the rest for some good $$$.

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