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Sm 420 Or 465 On 4.3l V6

Discussion in 'Early CJ5 and CJ6 Tech' started by shaun, Dec 14, 2017.

  1. Dec 14, 2017
    shaun

    shaun Member

    Lebanon, Ohio
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    i acquired a SM420 early edition, but was wondering which is better to install with a 4.3l v6. Currently have a running 225 on my 62, And want to keep this jeep for a long time but with future options ( 4.3l with 420 or 456) I know 420 are becoming scarce so parts may become harder to come by. So what’s everyone’s opinion, what are you running? Etc?
     
  2. Dec 14, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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  3. Dec 15, 2017
    fhoehle

    fhoehle Sponsor

    Harford Township, PA
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    I didn't like my SM420. My SM465 is good but big. Shifts ok but I really feel a T-18 is smaller and shifts better and just as durable. I'd vote T18
     
  4. Dec 15, 2017
    47v6

    47v6 junk wrecker! 2023 Sponsor 2022 Sponsor

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    My SM420 is fine, i guess. I rebuilt it to fix the 4th gear synchro issue and wound up with one in 3rd in exchange. Parts are annoying to source and the pre 1954 ones have no input shaft seal, so they leak if you park downhill. The sm465 is big as had been stated, but parts are more available. I have never had a t18. They will all work and they will all need some mods.
     
  5. Dec 15, 2017
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    Since you're asking opinions....
    I've run a few t-18s, a t-19, an SM465, and... my all time favorite by a mile was an NP465. It was solid as a rock, smooth shifting, well geared, and the t-case adapters that are available are short in lengths.
    My $.02 :blah:
     
  6. Dec 15, 2017
    73 cj5

    73 cj5 Not ready for the junkyard yet

    Clinton, Mississippi
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    NP435 is a smooth shifter unlike my sm465 but that may just be a worn out transmission...
    Edit: I did weld the shifter cane up yesterday but it still is just a dump truck transmission.
     
  7. Dec 16, 2017
    shaun

    shaun Member

    Lebanon, Ohio
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    I’m about to rebuild my 420. I have a 18 in my in my 62 right now along with a 225 odd fire. Looking to get a 4.3 and rebuild that and connect my 420 to it. To my understanding the T 18 is a bit weak for a 4.3l otherwise I would keep it in. I have found a 465 with bellhousing online for 600.00 but I thought that was a bit much. I replied with what I would pay for it but he never replied back. Novak said they would give a discount if I gave them my 420 in exchange for a 464. But still pretty expensive, even at this time of season
     
  8. Dec 16, 2017
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    :susp:
    Any of the heavy truck transmissions won't even be phased by the most abuse a V-6 could put through it. The T-18 in my V-8 dump truck has seen unspeakable abuse for the last 53 years and is still reliably in service.

    I wouldn't let that fear keep you from using it.
     
    Jrobz23, Daryl and Bowbender like this.
  9. Dec 16, 2017
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
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    All of these truck boxes T18, NP435, SM420 or SM465 are service rated to 2-1/2 tons. You’ll rip your new motor a part before tearing these things up. All of them will survive behind the torque of a big block let alone a V6 making at most maybe 300hp.
     
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  10. Dec 16, 2017
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
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    I've got both the T18 and SM465 in rigs - I like the gear ratios better on the SM465. Maybe it's me, but I really don't see much shifting difference in mine. Both had rebuilds done when installed since I had them apart to change the output shaft.

    I will say the SM465 is a BIG PIG, but with my hoists and tranny jacks it's not that much of a problem. It acts as it's own skid plate :)
     
  11. Dec 17, 2017
    shaun

    shaun Member

    Lebanon, Ohio
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    I messed up I meant to say I have a T90-A attached to a Dana 18. The T90 would not be able to suppport the 4.3L.
     
  12. Dec 17, 2017
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
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    They’ve been run behind lots of v8’s over years. Never had one so don’t know but a lot of guys kept them when they put a small block Chevy in their jeep.
     
  13. Dec 19, 2017
    shaun

    shaun Member

    Lebanon, Ohio
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    So would a 420 with a 4.3 be better, cheaper, more convenient,etc. or the T90 that’s already in my jeep matched with a 4.3l? I have the 420, rebuilding it and was going to put it in with a 4.3, but from what I am reading I could use my T90 with the 4.3 and possibly get an OD.
     
  14. Dec 19, 2017
    Bowbender

    Bowbender I'm workin' on it!

    Northern Minn.
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    One question you might ask yourself is if you want a lower first gear for "crawling", I think the four speed would give you that.
     
  15. Dec 19, 2017
    47v6

    47v6 junk wrecker! 2023 Sponsor 2022 Sponsor

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    You will never break the sm 420. The t90, maybe? The adapters are where the money is for the 420.
     
  16. Dec 19, 2017
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
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    x2 for both of the above. If you don't need a crawling granny low - then the truck 4 speed won't help. Neither the sm420/465 nor T18 has an OD internal gear - highest gear is still 1:1 (same as a 3speed). I'd recommend an external Warn OD either way. If your worried about the t90 durability, then consider a truck 4speed for sure, or possibly a T15 3 speed (not sure about adapting that one though - Tim can probably help).
     
  17. Dec 19, 2017
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    I'd go 420. Even if you never use the granny low first gear, second gear through fourth's gearing will be equivalent to the T-90's first through third, with the major difference of synchronization in the three gears that you'll most commonly use. T-90 is only synchronized in the top two gears as you know.
     
  18. Dec 19, 2017
    shaun

    shaun Member

    Lebanon, Ohio
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    I have currently 5.38 gearing in my Axle’s if that means anything as well. Like to go with 4.27 but that’s a whole different thread. I more than likely won’t be crawling and I do see the adapters for either T90 to 4.3 and 420 to 4.3 are where the price hits. 420 to 4.3 won’t need an adapter but will to hook to Dana 18 which is almost equivalent to the T90 to 4.3l adapter.
     
  19. Dec 19, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    The T-90 will be cheapest to set up, since it won't need another $500 adapter kit to connect to the Dana 18. Certainly the SM420 (or any of the truck 4-speeds) will be abuse-proof behind the 4.3L. It is possible to break the T-90, though IMO it would require some abuse on your part.The 4.3L is not that much more powerful than your 225.

    Both the truck 4-speed and an overdrive would be terrific upgrades for your Jeep.

    The T-15 has 6 splines and will bolt up to the Dana 18 using your existing output gear, but you'll need a different adapter to mate to the GM engine. I recall Ken (oldtime) had a thread on making a T-15 adapter ... looking. Found it. T15 To Dauntless Unfortunately the thread has the Photobucket ransomware disease. Maybe Ken can help if you need to see the pics. Here's the Novak adapter: Adapting the Chevrolet & GM Standard Shift Bellhousings to the Jeep CJ & FSJ Borg-Warner T14, T15 & T18 Transmissions Fairly inexpensive as such things go.

    Check out Novak's info page about the T-15 - The Novak Guide to the Borg-Warner T15 Transmission - some of it is not correct. It was never offered with an inline 6 in the CJ, and never offered with the 232 in any platform. The transmission you would want for your CJ came with the 304 V8 in the '72-73 Commando and '72-75 CJ, and was the standard transmission with the 258 in Wagoneers and J-trucks from 1974 through '79 (like my J10). There was also a long input T-15 that was the standard transmission for the 350, 304 and 360 V8 in Wagoneers and J-trucks through 1979, but that input shaft is way too long for use in a CJ.
     
    Last edited: Dec 20, 2017
  20. Dec 19, 2017
    47v6

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    I NEVER use first gear. I have 5.38 gears with a power lock in the rear and run 35"tires. I can run 60mph at 3500 rpm or so with no OD. The 420 shifts slow. Force it and you will grind gears and have problems. The t90 shifts better, but is not bulletproof. The adapter for the sm420 to d18 is 500 bucks...

    I don't know what adapters you need to mate the t90 to the 4.3 (t-90J input and matched cluster gear), but it could easily be in a similar range for a transmission the you *might* someday break.
     
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