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T90A to T90C Conversion

Discussion in 'Early CJ5 and CJ6 Tech' started by Warloch, Jan 29, 2013.

  1. Jan 29, 2013
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
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    Guys, I want to see if anyone has any 'hands on' experience with this as mine is just theory from reading. Jason is looking to get the lower gear swap and I 'believe' the only parts differing to allow the swap is the input and bottom cluster. All other parts lists I have seen show the other gears the same between the T90A and T90C.

    Please let me know if I have been in Don's Crack or not (the hallucinogenic one - get your minds out of the gutter) :D
     
  2. Jan 29, 2013
    oldtime

    oldtime oldtime

    St. Charles,...
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  3. Jan 30, 2013
    colojeepguy

    colojeepguy Colorado Springs

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    It was my understanding that the lower geared T90 internals would not work with the Dauntless, due to the shorter & smaller diameter input shaft. However, that posting mentions using Scout T90 parts...Ken, can you shed any light on this?
     
  4. Jan 30, 2013
    oldtime

    oldtime oldtime

    St. Charles,...
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    I believe your interested in more IH Scout details concerning this paragraph ?

    Like I previously stated its just a concept that I put together.
    I was not fully interested so did not fully pursue the concept in all detail.
    I am not fully interested because I don't feel that the T90 is the optimum component behind a D225 engine.
    Probly better than a T86 AA but inferior to T14 / T15 Borg Warner three speed transmissions.

    At this time the only details in question are the exact lenghts of the various IH T90 maindrive gears and the diameters.
    I'll check into those details when I can.
     
    Last edited: Jan 30, 2013
  5. Jan 30, 2013
    nickmil

    nickmil In mothballs.

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    Just to throw another nugget into the IH T-90 parts. Some IH T-90 main drive gear and cluster gears had the tooth helix reversed from the Jeep and Studebaker versions.......
     
  6. Jan 30, 2013
    colojeepguy

    colojeepguy Colorado Springs

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    I'm running a T90J behind my Dauntless. It's the standard long input shaft version with a 2.79 1st gear, and I'm using a common T90-GM adapter plate that's a couple inches thick. It's given me good service, but a little deeper 1st would be welcome.
    I had planned to do a 4 speed conversion with a T98 I bought from Warloch, but had to sell it due to
    financial concerns.
     
  7. Jan 30, 2013
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
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    There is no way to adapt the T90C to the V6 in a 'practical' manner. I looked at it for years before giving up and just moving on to the 4 speeds.

    We will figure out something to get you some deeper gears Doug :)
     
  8. Jan 30, 2013
    colojeepguy

    colojeepguy Colorado Springs

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    Thanks, Chuck! I figured that was the answer.
    One of those "you can't get something for nothing" kind of deals...
     
  9. Jan 30, 2013
    oldtime

    oldtime oldtime

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    It would probably be a first but I still think a person could adapt the T90C onto a D-225 bellhousing if they were determined enough.
    Use caution here because IH Scout T90 specifications are very limited and the parts will be vary scarce indeed.
    Here's what I've determined so far....

    There are only 3 of 7 Scout T90 maindrives that can possibly fit the application.
    As Nick mentioned the other 4 have left cut helical gears and certainly will not adapt.
    So here then are the only 3 prospective T90 maindrives for the conversion.

    1) 1961 -1962 IH maindrive OAL = 8-3/8" right cut helical 16 tooth BW # T90 C-16
    2) 1963 only IH maindrive OAL = 12-9/16" right cut helical 16 tooth BW # T90D-16
    3) 1963-1968 IH maindrive OAL= 8-3/8" right cut helical 16 tooth BW # T90C-16A

    I believe these were likely all from 4 cylinder IH applications but IH detail is not my focus.

    Next concern:
    The D-225 has a BOP bellhousing depth of 6-3/8".
    The ideal "stick out" (SO) length (target length) for D-225 engine without using a bellhousing adapter is 6-3/4".
    T90 maindrive gear OAL is right about 2" longer than the maindrive gear SO length.
    #1) and #3) maindrive gears will have a SO length of 6-3/8" which is very close to the 6-3/4" target length.
    That said; #1) and #3) are not great options because one must bolt the T90 direct onto the BOP bellhousing without an adapter plate.
    This implies that the D-225 engine will be into the firewall unless the rear engine support crossmember is moved foreward.

    The ideal stick out length when using a common (2-5/8") bellhousing adapter is 9-3/8".
    #2) maindrive gear will have a stick out length of 10-9/16".
    This implies that over 1" would need to be cut off the #2) maindrive gear to fit it if using a standard bellhousing adapter.
    With too much cut off; a modified maindrive will likely cause clutch release problems.
    To make #2) fit without cutting the length one might consider adding more thickness to the standard 2-5/8" deep adapter plate.
    I estimate the ideal BOP adapter to be 3-3/4" thick.
    This extra adapter thickness will move the engine foreward about 1-1/8".

    So I fully expect that a T90C could possibly be mated to the BOP bellhousing.
    I have no data concerning the diameters nor the spline count for those particular IH maindrive gears.
    Therefore the appropriate clutch disk remains in question.
     
  10. Jan 30, 2013
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Last edited: Jan 31, 2013
  11. Jan 31, 2013
    oldtime

    oldtime oldtime

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    Yeah
    In the case of T90 C mated to BOP; finding or making an adapter is not the main issue.
    The main concern is finding a 16 tooth RH helical maindrive gear with an appropriate length and hopefully at 1-1/8" diameter.
    I only mentioned the IH possabilities but Nick claims that Studebaker also used a T90.
    AFAIK the Studebaker maindrives could also be a possability.
    Here one just I found at EBAY # 300578949116.
    It's a Borg Warner # T90AA-16B
    Not really sure if that ones a 16 or an 18 tooth drive.
     
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