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Thread: Discrete shift torque mode

  1. #1
    Advanced Tuner
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    Dec 2014
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    Discrete shift torque mode

    I've really been trying to understand why you would want to use Discrete Shift Torque Mode for shift pressures. In my tune, there is an enable table, Low-Mid and Mid-High threshold tables and finally Low, Mid and High tables.

    My understanding is that when enabled, the computer will use "preset" values for the shift torque instead of the actual shift torque in order to determine the correct shift pressure to use.

    I'm unclear about a few things:

    1. Why would not want to use the actual shift torque to determine the correct pressure to use in the first place? I know the help file mentions that it makes it easier for the transmission to "learn" the correct pressures, but what good is learning the pressure if it's not for the correct shift torque anyway?

    2. The shift torque threshold tables that detemine if the Low, Mid or High tables should be used for the pressure don't seem to make much sense. For example, for my 2->3 shift, anything under 22 ft. lbs of actual shift torque would use 37 as the pressure lookup, between 22 and 155 ft. lbs, it would use 203 for the pressure lookup and anything over 155 ft. lbs would use 369 for the pressure lookup. So if I had 37 ft. lbs of acutal shift torque, the computer would actuall use 203 ft. lbs for the lookup!! That makes absolutely no sense to me.

    What am I missing here? Think I would be better off disabling discrete shift torque and just letting the computer use the actual shift torque values instead? Just not quite sure I understand the benefit of discrete shift torque.

    I would just try it, but I need to get my car inspected on Monday and don't want to reset the emissions readiness test status right now (can take days to reset).

    Thank you!

  2. #2
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    Bump. Anyone have any input on this (Discrete Shift Torque Mode)? My car (2012 Impala) comes with it enabled for every shift. Just wondering if there are any advantages or disadvantages of disabling it?

    You'd think that you'd want the trans pressure to be set depending on the *actual* shift torque and not just a "low, med, high" value? Just trying to understand why they would do this. They say that it helps the trans "learn", but if it's learning inaccurate values, what good is it?

    I' did just try disabling it, but I'll need to drive the car more before I can tell if it makes any difference - and if so, whether it's a good or bad difference.

    Want to make sure I'm not doing my trans any harm in the meantime though....

    Thank you!

  3. #3
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    Well, I tried disabling Discrete Shift Torque briefly and did NOT like the results at all! Shifts were very erratic and just not good.... Don't quite understand it, but I'll be leaving it enabled going forward. :-)

  4. #4
    Tuner in Training PHLTHS's Avatar
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    Hi Champ,

    Sorry to resurrect an old thread, but I have been doing quiet a bit of research about Discrete Shift Torque and how it works. I'm currently in the middle of tuning my Colorado with a 6L50 in it.

    From what I can tell the two threshold tables:

    [TCM 15921 Discrete Shift Torque Low-Mid Thresh]
    [TCM 15922 Discrete Shift Torque Mid-HighThresh]

    are used as a threshold limit to determine which of the three main Discrete Shift Torque tables are used in order to report a Different Torque Number from the Actual Torque Number.

    [TCM 15923 Discrete Shift Torque Low]
    [TCM 15924 Discrete Shift Torque Mid]
    [TCM 15925 Discrete Shift Torque High]

    As an example with the attached image, if the actual torque for the 1>2 shift is less than 150NM then it'll report a 0NM torque figure so the auto will then use the 0NM column from the Base Shift Pressure 1-2 table. If you are over 150NM for the 1>2 shift, then it'll use the value in the [TCM 15924 Discrete Shift Torque Mid] table as the reported Torque Number instead. In this case 300NM.

    As to why you would want to fug the reported Torque Values, my research has mainly led me to believe this is to help with the Adapt learning and also it basically it gives you 3 levels of pressure for your shifts depending on use. As with Discrete Torque turned off, the pressure value would increase graduly as the code interpliates between the aboslute values in the columns on the Base Shift Pressure tables.

    However, with Discrete Torque turned on, it'll just use the absolute values in these tables provided the three Main Discrete Shift Torque tables are mapped to the same torque values as the coloumns of the Base Shift Pressure tables like the factory tune image attached.


    Hopefully someone else can chrime in here, maybe even Chris from HPT might know of a situation you might want to use this feature?

    Cheers.
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    Last edited by PHLTHS; 4 Weeks Ago at 06:22 AM.
    HSV W427