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Thread: Transmission tuning help - 8L90e

  1. #21
    Tuner
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    Nov 2018
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    I just invested in the tuning schools gm transmission book. It will be here in 2 days or so.
    There is just too many ways to mess things up with an unlocked TCM.

  2. #22
    Tuner
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    Aug 2019
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    Cleveland, TN
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    educational material is always good. let us know what you figure out

  3. #23
    Tuner in Training
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    So i can't figure out how to properly calculate the Low adjust value.
    Here are the parameters from the 2015.5 Yukon Denali:

    The final drive ratio is 3.23:1 (Differential gear ratio)
    The transfer case ratio is 2.69:1
    1st gear is 4.56:1
    6th gear is 1:1
    8th gear is 0.65:1

    The calculated Low Adjust Value is shown to be 0.73
    Can someone explain to me how it got calculated?

  4. #24
    Tuner
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    I thought the transfer case was 2.42
    If that is the case then its you are going at 73% as fast in 4wd low as you would in drive (no 4wd lo)

  5. #25
    Potential Tuner
    Join Date
    Mar 2019
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    New to the forum, I have the same setup as the OP (Jeep with L86 and 8L90). Also looking to get into the transmission and understand what all this means.

    I?m not sure what the Yukon transfer case ratio is, but I believe the correct way to turn it into a percentage is to divide 1 by the ratio. So, a 2.42 would be .41 and a 2.69 would be .37. Neither of which get us to .73. That would be a transfer case ratio of 1.37 to 1 which I doubt anyone would make.

    Interested in getting this figured out!



    Quote Originally Posted by fifty View Post
    I thought the transfer case was 2.42
    If that is the case then its you are going at 73% as fast in 4wd low as you would in drive (no 4wd lo)

  6. #26
    Tuner
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    I’m finding a 2.69 and 2.42 low ratios. But apparently there is a different ratio of you got the tow package or not...

  7. #27

  8. #28
    Tuner in Training
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    I came up with the same calculations as conquistador (forum user). If anything the Low Adjust value should be 1/(transfer case gear ratio).

  9. #29
    Tuner in Training
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    Ok so this is still an open and unresolved thread. Can someone please explain to us how to get to the correct Low Adjust Value?
    Thank you!

  10. #30
    I've had this issue in multiple STOCK vehicles. They are not following the actual commanded tables for the downshift, thus wants to stay in 8th (or 10th gear) for way too long. I've seen it like it doesn't actually recognize the actual accelerator pedal and only uses the first 2 columns (0% throttle and 6% throttle and its hovering there). This issue seems to be an actual Operating system issue or another issue which cannot be explained.

    I hope to see some resolution for this.

  11. #31
    Advanced Tuner IARLLC's Avatar
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    Aug 2016
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    Since the number don't really add up or divide or.....Maybe it would be possible to just try .72....71.....70....etc and watch the results?