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Thread: Trans hits 4th hard with light/no throttle, fine with moderate throttle

  1. #1
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    Default Trans hits 4th hard with light/no throttle, fine with moderate throttle

    I believe this is a tuning issue, ever since I raised the speed at which the trans engages OD it's been like this. It's much worse now with the shift kit, but it's the only time the trans is harsh, so I really don't think the shift kit is to blame. If I'm coasting down a hill and the truck hits its shift speed, it drops it way hard. Same as if I'm loafing along just enough to get it up to the minimum OD upshift speed. I believe I'm to blame here, but don't know how to smooth it back out. Anyone?
    Attached Files Attached Files
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  2. #2
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    Without even looking at the tune, I was thinking today: could it be that my torque converter is locking up simultaneously with the shift? If so, how would I get around that? I changed the 3-4 shift speeds, but not the 4th lockup/release tables.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  3. #3
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    Well it's not the torque converter locking during the shift, at least I hope not. I made an experimental tune that forced it to wait until 95kph to lock up in 4th and it still hit harder than a WOT 1-2 or WOT 2-3. I'm seriously worried I'm going to break a hard part, i.e. the sunshell because of a 3-4 upshift with minimal throttle at 40mph. Here's the tune I'm running now, I tried to make it so the torque converter locks after it shifts instead of being commanded to be locked before the upshift ever occurs. This tune is still beating my trans to death and it was like this before the shift kit, it's just worse now. I have a stock 4th gear servo too, so I have no idea what could be causing this at this point unless altering the VE table has somehow changed something?
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  4. #4
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    I also noticed there is no torque reduction on the 3-4 upshift and the shift times are zeroed there from the factory. I ASSume those don't need to be screwed with to get my desired end result. When the truck was bone stock, I don't remember it acting like this.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  5. #5
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    Default Trans hits 4th hard with light/no throttle, fine with moderate throttle

    I'm on my phone so I can't see your tune but it sounds like the shift kit has quickened the shifts do less psi is needed for the same shift time. With the commanded shift time set to 0, the tranny isn't trying to modify pressures to hit the shift time. It's only shifting on pressure only. I can't remember the table number but there is one that defines the 3-4 shift psi vs engine output torque. You should log it and see exactly at what output torque it's happening below and lower your shift pressure in there

    But I think your seeing it with the higher shift speed because it takes more throttle and there is more rpm drop at that shift point now

    I apologize if I'm in left field, that's just what it sounded like reading it and like I said, I can't see the tune right now
    14 GMC Sierra
    5.3L CC SB 4x4
    Basic tuning....

  6. #6
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    I'm going to re-engage this after class, but I was doing some pondering today and came up with an idea. I believe the problem lies in the fact that my torque converter locks up in 3rd prior to the transmission shifting into 4th. I was under the impression that the converter would unlock upon an upshift, but apparently that's not the case. Over the course of my pondering, I came to recall that it seemed, with my experimental tune, that the TCC would unlock after shifting into 4th, then stay unlocked thus implying otherwise.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  7. #7
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    Well I couldn't wait until after class, so I did it before. Since the trans was warm though, I can't be certain I've fixed it. Initial impressions are that it is fixed, but I don't like it. I can't cruise through town with the converter locked as much. Doesn't seem I have a choice.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

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