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Swap T90 Transmission Behind A Dauntless V6?

Discussion in 'Early CJ5 and CJ6 Tech' started by VintageIron41, Nov 12, 2023.

  1. Nov 12, 2023
    VintageIron41

    VintageIron41 Member

    Dayton, OH
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    Hello and thanks for taking time to read this.

    My 1970 CJ5 drivetrain has a leaky transmission, I've done the easy things, reseal the bottom plate where it was seeping and teflon taped the speedometer threads. Over the winter I'd like to address the leaks, my question is, if rebuilding the transmission (T14?) would it bet better to find a T15 to rebuild and swap in? Am I right in reading that the T15 is a more robust transmssion?

    Thank you!
     
    Last edited: Nov 12, 2023
  2. Nov 12, 2023
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    The T15 is a pretty strong transmission, likely the strongest 3 speed. I’ve never done a T15 in anything that it wasn’t available in (AMC intermediate). You need to know the input shaft stick-out length and trans bolt pattern, front and back.
    -Donny
     
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  3. Nov 12, 2023
    Fyr-guy

    Fyr-guy New Member

    British Columbia
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    I'm in the same situation. My t86 has seen better days and is not worth rebuilding. Is there a T90 variant that would swap right in? Don't mean to hijack your thread.
     
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  4. Nov 12, 2023
    Andrew Theros

    Andrew Theros Member 2023 Sponsor 2022 Sponsor

    Los Osos, CA
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    I may be mis understanding your question but here goes anyway.
    Your T14 doesn’t have a pan or speedo cable, both of those are on your D18 transfer case.
    As for swapping a T15, I am clueless but I would guess that adapters would be involved.
    Rebuilding a T14 is pretty straightforward, but based on my experience, I would read up on tolerances and min/max measurements on the pcs you will reuse. Mine is not sounding very healthy after 2 years and 2k easy miles.
     
  5. Nov 12, 2023
    Ollie2009

    Ollie2009 Member

    Ann Arbor, MI
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  6. Nov 12, 2023
    colojeepguy

    colojeepguy Colorado Springs

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    T14 is a 10 spline output, unique in the Jeep world. T90 or T15 would have a 6 spline output. So you're going to need a 6 spline gear for the transfer case.
     
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  7. Nov 12, 2023
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb

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    Just my opinion. The T-14 will be the weakest trans. The t-15 will be likely be the strongest but it is longer overall and would likely be the most difficult to adapt. Especially since they were never offered behind the V-6 as far as I know. As Donny said above they were only offered by AMC behind the V-8 engines. Also I have found some of the parts for the T-15 are a bit hard to find. As far as the T-90,It would likely be about as strong as the T-15 and parts seem to be a somewhat easier to come by. Probably because they were so widely used and for lots more years. however adapting them to the v-6 is not my expertise:shrug:,:study:. I will say this about the T-90. Years back my brother had a friend with a 3B with the t-90/D18 and a hopped up Ford 289 4bbl.He was a hot rod kinda guy, every where he went he was spinning and leaving black marks on the pavement with it. He drove that jeep 10 years and finally sold it. Never did have the first problem with the T-90 or the D-18. But rear axles were another story.
     
  8. Nov 12, 2023
    colojeepguy

    colojeepguy Colorado Springs

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  9. Nov 12, 2023
    Oldpappy

    Oldpappy A.C. Fults - Curmudgeon at large 2022 Sponsor

    East Tennessee
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    The easiest way to put a T90 behind the V6 is to source the 71 one piece bell housing, drill and tap it for the T-90.

    The input shaft for the T-90 has to be the long one as used in the trucks, so that has to be swapped. I just sold one of those bell housings which had been fitted for a T-90. Problem is that bell housing was only made for one year before Kaiser sold out to AMC, so they are a bit scarce, but they can be found.
     
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  10. Nov 12, 2023
    duffer

    duffer Rodent Power

    Bozeman, MT
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    Two straight forward ways to put a T90 behind the 225. 1: use the T86 case and replace all the internal parts with T90J pieces. 2: use a complete T90J with the 2 5/8" adapter plate. Equally good. The 68 CJ 5 I bought from Fireball has the adapter plate/T90J setup.
     
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  11. Nov 12, 2023
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
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    Just my thoughts.....not sure there is much strength difference between the t90 and the t14. Having been through both of them on the bench, the T14 parts are a bit bigger, but that doesn't mean it necessarily is stronger as a complete unit. Behind a v6, I think you are fine with either one (or t90 guts in a t86 case). I don't think you start stressing these transmissions too much until you put them behind v8 power. There are 2 big advantages to the T14 over the t90: 1st gear is synchronized whereas the t90 is not, and depending on usage, the 3.1 1st gear ratio of the T14 is lower than the 2.79 of the t90j (long input shaft). As Doug mentioned, the T14 has a different output spline count (10) than just about all other transmission options (6). This affects how the trans connects with the transfer case, and it adds additional complications (parts) if switching between the two different output spline counts. And this gets even more complicated/expensive if dealing with an OD or low gears in the D18. If strength is really a concern, the T15 is much better, but adapting to buick v6 is more complicated and expensive - so much so that I'd then consider going truck 4 speed? Honestly (and yes, full disclosure, I have a well used T14 in my jeep), if you have a T14, its probably best option to rebuild it unless you REALLY have a desire for more strength (v8 swap) or granny low (hard core off-road usage) - then its a truck 4 speed swap as opposed to a T15. Same with if one has a T86 (or a t90j swap) behind the v6, then I stay with that route as well and go T90 (or t90 guts in a t86 case) unless there is REALLY a need or desire to go 4 speed.
     
    Last edited: Nov 12, 2023
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  12. Nov 12, 2023
    VintageIron41

    VintageIron41 Member

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    Thank you everyone for your replies, it sounds like my best bet then is to rebuild the T14, again thank you for your time taken to reply!

    Dave
     
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  13. Nov 12, 2023
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
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    Rebuilding the T14 is easy. That said pay very close attention to the gasket on the front bearing retainer when rebuilding, none of them fit good and they tend to block or slow the oil flow to the front bearing causing premature wear. My T14 has way more than 180,000 miles on the original gear set. I have rebuilt it but have used all the original hard parts.
     
  14. Nov 12, 2023
    jeep2003

    jeep2003 Well-Known Member

    Upstate NY
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    Id rebuild the t-14 for sure. Good match for the v6. but sounds like most of your leaks are from the t case which is always the case theres not much to leak on the transmission.
     
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  15. Nov 12, 2023
    Daryl

    Daryl Sponsor

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    T15 is an easy swap with parts readily available. The only good thing about a t90 is that it fits in a garbage can with the shifter still installed and besides a t84 is the weakest transmission ever installed in a jeep. A rebuilt t14 can also be easily sourced if you are not handy with modifications and driveshaft alterations required with a t15 swap.
     
  16. Nov 13, 2023
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    :rofl:
     
  17. Nov 13, 2023
    Fyr-guy

    Fyr-guy New Member

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    Great information, thank you all.
     
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  18. Nov 14, 2023
    duffer

    duffer Rodent Power

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    I don't have quite that level of disdain for the T90. It wasn't anywhere near as over-engineered as the D18 but still a decently solid transmission capable of handling considerably more power than either 134 could muster. The T84? If one actually has one of those in hand, they are TINY. Willys wasn't the only application of those either. My 41 Nash 600 coupe sports a side shift T84. Those wouldn't make a bad motorcycle trike transmission if they actually shifted worth crap:rofl:
     
    Last edited: Nov 14, 2023
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  19. Nov 14, 2023
    colojeepguy

    colojeepguy Colorado Springs

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    I blew up 2 or 3 T90's, but it was a heavier vehicle (IH Scout) with a decently strong Chevy 327 and perhaps most importantly, I was 17 years old :lol:
    Years later I put my CJ together with a T90 and it lived for over 20 years behind a Dauntless. i drove it much more conservatively!
     
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