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T90A vs T90C, What a difference!

Discussion in 'Early CJ-5 and CJ-6 Tech' started by Brian P, Feb 1, 2009.

  1. Feb 1, 2009
    Brian P

    Brian P Member

    Clarkdale Arizona
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    Recently I realized that my transmission was going south but did not really know how bad until I tore into it. My T90A was beyond any practical repair :(

    So I decided to Get another one from Herm, Seeing how I had to spend the bucks anyway I thought I would cough up the extra and give the T90C version with its lower 1st and 2nd gears a try...........And its great! I am not wishing for a 4 speed anymore, This is a great option for anyone with a T90A wanting lower gears but cant amortize a proper 4 speed conversion.

    The lower gearing made a new machine out of the old cj, Its noticeably easier to take off in high range from a stop and It made a HUGE difference climbing around in low range :) ........ And I dont have to ride the brakes hardly ever anymore going back down these steep grades :) The gears are just low enough the engine can now hold the rig back unassisted 90% of the time :)

    In high range the lower 1st and 2nd are the perfect dirt road cruising gears ( for me anyway ) with the 5.38:1 differentials, Second gear on the T90A was a little to fast on the rough roads locally unless you were nearly lugging it just above idle, Letting off the throttle for a rough spot usually meant a shift into 1st. Second gear in the T90C is low enough that you can slow down for a rough spot and gently throttle out the other side without shifting into 1st about 80% of the time and it is not over revved when you get back up to speed...........In fact my manifold vacuum gauge shows slightly higher vacuum ( 1hg - 2hg ) at the speed I like to drive in second.

    There is a slightly larger gap between 2nd and 3rd so it would mean a slightly slower pull in second through the mountains once a shift into second had to be made but its not hard to get used to, In that respect the T90A version would be a little more "street friendly " by comparison.

    I thought I would post this for anyone thinking about this option, As I am very happy with it :)
     
  2. Feb 2, 2009
    sammy

    sammy Coca-Cola? Sponsor

    Albuquerque, NM
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    Brian, I wonder if you had an OD if you could just OD quick in 2nd and then jump into 3rd? Just an idea. Sounds like a nice transmission
     
  3. Feb 2, 2009
    Brian P

    Brian P Member

    Clarkdale Arizona
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    After running both versions I would think the T90C and an OD would make a good combo.
     
  4. Feb 2, 2009
    sparky

    sparky done Staff Member Founder

    Toowoomba, QLD
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    Brian,
    Thanks for the helpful post. I've been considering the transmission of choice for my new project. I want a three speed for the cost aspect of it and I just kinda like the three speeds anyway. Sounds like you and I do a lot of the same type of driving too.

    [​IMG]
     
  5. Feb 2, 2009
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

    Medford Mass USA
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    IIRC the T-90C is only compatible with the F134. V6s need not apply. There's no long input shaft available for the T-90C.

    It would work with the Pinto 2000/2300 swap though.
     
  6. Feb 2, 2009
    sparky

    sparky done Staff Member Founder

    Toowoomba, QLD
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    Dangit. Guess my search continues since I only have V6s. :(
     
  7. Feb 2, 2009
    Homebrew2

    Homebrew2 Member

    Dunlap, CA
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    Great post Brian! <wish there was an FHead smiley that was as recognizable as the V6>
    I don't knoww if I have a "C" or not, but I think so. Unfortunately, when I do the calcs and use GPS in these hills, after normalizing rolling tire diameter, the 5 mph diff between 1st and 2nd at various PRM's, I can't say for sure.

    I'm responding because what you describe as the "C" performance is exactly what I have ... I have to UPshift sometimes because the chosen gear is too low ... in 1st, low range steep descents on old trails is almost too slow and, in just slightly wet conditions, a slide occurs (tires inflated for paved mountain driving).

    As has been eluded to, my main interest in OD is splitting 2nd gear on 5%-10% grades ;) :beer:
     
    Last edited by a moderator: Feb 2, 2009
  8. Feb 3, 2009
    jeeper50

    jeeper50 jeeps 'till I die

    Gawja
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    Wasn't the "c" installed in 64 and later CJs with the 4.27 gears?
     
  9. Feb 11, 2009
    Schlotka

    Schlotka default member

    Weed, CA
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    I second the improvement of the t-90c gearing. I had Herm install the c's gears in my t-90a when he rebuilt it. Not a big change, but you notice it in underdrive.
     
  10. Feb 11, 2009
    oldtime

    oldtime oldtime

    St. Charles,...
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    The following is an excert from
    "Everything You Ever Wanted to Know About CJ-3B Speed and Then Some".
    This also applies to models CJ-5,6.

    For our model of jeep there were two differing transmission input ratios in use.
    See bulletin # 600:

    http://www.film.queensu.ca/CJ3B/Photos/Tech/ServiceBulletins/SB600Tranny.JPG

    Since slightly more hp was realized by the 134 engines progression,a slightly faster vehicle speed became feasable.
    So in model year 1963 the transmission low gear ratio was increased.
    This transmission change was done to offset the simultaneous axle change from the 5.38 ratio to the 4.27 ratio.
    With this combination of 3 changes including the ,engine, transmission and axle;
    the maximum vehicle speed would be increased without adversely raising the minimum (crawl) speed.

    In the transmission this change was manifest by changing the main drive tooth count from 18 teeth to 16 teeth
    plus also changing the driven cluster gear tooth count from 33 teeth to 35 teeth.
    Remember these particular driving and driven gears can only be interchanged as a set.

    Here then we have two different T-90 variants that were used in the 3B.
    Below are the gear ratios for both the pre 1963 (early) Borg Warner T-90 A and the post 1962 (late) T-90 C.

    T-90 A T-90 C
    (INPUT) (INPUT) (OUTPUT)
    1st gear 2.798 3.339 1.00
    2nd gear 1.551 1.851 1.00
    3rd gear 1.000 1.000 1.00
    reverse 3.798 4.531 1.00

    As you can see from the numbers the velocity of the transmission output drive will be affected by gear selection.
    The transmission velocity is to be understood as a numerical ratio, input to output.

    Low gear ratios reduce a vehicles resistance to the force by decreasing traveled distance.

    The minimum output for the early T-90 A in 1st gear is ( 600 divided by 2.798 =) 214 rpm.
    The minimum output for the latter T-90 C in 1st gear is ( 600 divided by 3.339 =) 180 rpm.

    High gear is always a straight through drive without gear reduction.
    So the maximum output for both T-90's in 3rd gear is 4000 rpm.
    As you can now see the T-90 C has a greater gear ratio spread.
     
    Lee Bennett likes this.
  11. Feb 11, 2009
    sparky

    sparky done Staff Member Founder

    Toowoomba, QLD
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    Good info, thanks oldtime. :beer:
     
  12. Feb 11, 2009
    Brian P

    Brian P Member

    Clarkdale Arizona
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    Good historical info. Thanks for sharing.

    I have driven mine quite a bit since installing the T90-C version, When used with the 5.38 differentials it really improves the trail crawling and reduces shifting when dirt road driving. The increased spread between 2nd and 3rd is not hard to get used to.
    I dont mind the top speed limitation of the 5.38 gears ( I have been stopped twice for driving to slow :oops: )
     
  13. Sep 16, 2018
    1957Willys

    1957Willys Member

    Birmingham, Alabama
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    Does the T90C have more gear whine than the T90A in first and second?
     
  14. Sep 17, 2018
    Keys5a

    Keys5a Sponsor Sponsor

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    I've switched between the two T90 versions over the years and can't say one has more whine than the other. Most of the gear whine comes from the intermediate gear in the transfer case, especially if the the thrust washers and bearings are less than perfect.
    I have also run a short shaft (F134) T90 behind a Buick 198 using the 198 shallow bellhousing.
    Tim's 2009 comments say you can't run a V6 with the short shaft. There also used to be an aftermarket bellhousing that mated the short shaft with the BOP block pattern for the 225.
    -Donny
     
    Last edited: Sep 17, 2018
  15. Aug 6, 2019
    1957Willys

    1957Willys Member

    Birmingham, Alabama
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    I'm late replying but it's only in first, second and reverse.
     
  16. Aug 6, 2019
    1957Willys

    1957Willys Member

    Birmingham, Alabama
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    I've already done the tapered bearing conversion on the transfercase.
     
  17. Aug 6, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Yes, my comment is out of date or mistaken or both. Novak offers a T-90 to GM adapter that uses the short shaft and adapts either the T-90A or C. Per Donny's comments, it seems there were at least a couple of ways to adapt a V6 using the short shaft back in the day.
    Adapting the Chevrolet & GM Standard Shift Bellhousings to the Jeep T90 Transmission

    Regarding whetehr The A or C would be noisier, I don't see why either would be. Both have a straight-cut 1st and R, which whines loudly. The amount of whine depends on the gear bevel angle; the more bevel the quieter yet weaker the gear. I expect they have the same bevel, so same noise. Except for 1st-R, I'd think the T-90 generally would be the same as the rest of the B-W 3 speeds wrt noise, ie not noisy. The T-90 was also used in passenger cars, where the transmission is expected to be quiet.
     
    Last edited: Aug 6, 2019
  18. Aug 6, 2019
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    I've owned both, and didn't notice a whine in either.
     
  19. Aug 9, 2019
    Rick Whitson

    Rick Whitson Detroit Area Sponsor 2019 Sponsor

    I live South of...
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    I think I read in the FSM that the Dispatcher, column shift T 90 had different gearing than the floor shift, don't remember what the difference was, but I think second was higher for better street use. Just something to consider.
     
  20. Aug 9, 2019
    Keys5a

    Keys5a Sponsor Sponsor

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    The column shift used on the Tux is a T90c, otherwise the same as the cane shift T90c. These were all used by the later 134-4 Jeeps with the 4.27 axles. I'd be suprised if the DJ5 had different transmission gear ratios. The T90c has a lower 1st gear and a slightly lower 2nd gear as opposed to the T90a and T90j.
    -Donny
     

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