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Thread: 4L80E Downshift Tuning For Towing? (Engine Braking/Grade Shifting)

  1. #1
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    4L80E Downshift Tuning For Towing? (Engine Braking/Grade Shifting)

    Hey Guys,

    New to the HPTuners world, having a great time with it so far, but I had a question. I was wondering if it were possible to program the vehicle (2002 Suburban 2500, 6.0L, 4l80E) to downshift while in Tow/Haul mode as if you were manually bringing down the PRNDL321 shifter? Would be wonderful to help with engine braking and getting the vehicle slowed down while towing. I am just not sure if this would be possible on this vehicle, does anyone know?

  2. #2
    Tuning Addict 5FDP's Avatar
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    I don't think downgrade shifting is possible to program or something those OS's do.

    I know on the way newer 6L90e transmissions in heavy duty trucks they will downshift to a lower gear when coasting down hills to help slow it down.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  3. #3
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    Quote Originally Posted by 5FDP View Post
    I don't think downgrade shifting is possible to program or something those OS's do.

    I know on the way newer 6L90e transmissions in heavy duty trucks they will downshift to a lower gear when coasting down hills to help slow it down.
    I do not see why you could not program the part-throttle shift tables to accomplish the same thing. When you let off to 0% throttle you could set the 4-3 and 3-2 shift speeds at 0% fairly high in tow-haul and it would cause it to downshift and slow down. I have thought of doing the same thing in my 2002 Express. My 2006 Ram and my 2012 and 2014 Titan all did the downshift to keep the speed down so long as you were running with the cruise set.

  4. #4
    Tuner in Training bigwillys58's Avatar
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    i believe that because of the way a 4l80e works that this would not be possible with the gear selector in "D". engine braking only happens in manual 3, 2, and 1 because then and only then are the over-run clutches engaged.
    08 GMC rcsb 2wd. 4.8/4L80e with a dollar store turbo.
    best so far of 7.25 @ 97.4 1/8 mile

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    Bringing this back from the dead. I tried to modify the part-throttle shift tables to accomplish what Fast4.7 was saying. When I modified the table at 0% throttle, there was no difference. Thought I would try to modify the next column over too. Again, felt no difference when off the throttle, but then if given it just a sliver of throttle it would want to down shift.

    Anybody have success getting there 4l80e to down shift at 0% throttle to help with engine braking?

  6. #6
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    Quote Originally Posted by ScotchBonnet View Post
    Bringing this back from the dead. I tried to modify the part-throttle shift tables to accomplish what Fast4.7 was saying. When I modified the table at 0% throttle, there was no difference. Thought I would try to modify the next column over too. Again, felt no difference when off the throttle, but then if given it just a sliver of throttle it would want to down shift.

    Anybody have success getting there 4l80e to down shift at 0% throttle to help with engine braking?
    I have been playing around with this a little as well, I plan to give it another go soon. I am wondering if it doesn't reference that 0% throttle column or something.