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Thread: Allowing converter to slip on 6L80/90 at cruise?

  1. #1

    Allowing converter to slip on 6L80/90 at cruise?

    I've been looking over the torque converter clutch tables for the 6L80 on my factory tune and noticed that it is setup to slip pretty much all the time. What's the benefit to having the torque converter slip while cruising down the highway?

    I think mine is setup so that at 60 mph it is slipping only about 25 rpm.

  2. #2
    Tuner in Training
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    Aug 2014
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    Im not sure exactly why but it seems as though all 6l80/90 were set up that way from the factory. If i change these tables to 0 desired slip i feel increased shudder or surge when accelerating in 6th gear.
    11 Sierra Denali

  3. #3
    Quote Originally Posted by Jmandernach View Post
    Im not sure exactly why but it seems as though all 6l80/90 were set up that way from the factory. If i change these tables to 0 desired slip i feel increased shudder or surge when accelerating in 6th gear.
    I'll probably do some playing with over the next few days. My setup won't use 6th much since I have tall gears and large tires.

  4. #4
    Tuner in Training
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    Aug 2017
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    I raised the TCC desired slip tables on my 17 6L80 and that seems to have cured my shudder/ surging issue at light-medium throttle cruising.

  5. #5
    I ended up looking at the torque at cruise and wrote 0's in the center of the cruise rpm/torque with a transition to unlock, and at cruise it commands 0, but still slips about 10 rpm in 4th, 5th, and 6th. I disabled torque converter clutch completely in 1st, 2nd, and 3rd.

    I don't get any shudder or surging though. I did initially because I assumed it was using less torque than actual causing the torque converter to lock/unlock. There is a slight increase in vibration, which might be why it is commanded to slip a little.

  6. #6
    I have the same issue, I would rather lock the TCC as the economy, wear and temperature benefits are there but no end of playing with Regulator and apply ramps have been able to rectify it. If I aim for 0 slip and attempt to have no slip the however the TCC seems to drop pressure under light load despite the setting on the offset to max, it's like there is a missing parameter that forces the TCC pressure to reduce until slip occurs, like 02 hysteresis. its probably an economy setting to reduce pump pressure but it makes the TCC drop out and grab cyclically at low load.

  7. #7
    Quote Originally Posted by 4wheelinls1 View Post
    I have the same issue, I would rather lock the TCC as the economy, wear and temperature benefits are there but no end of playing with Regulator and apply ramps have been able to rectify it. If I aim for 0 slip and attempt to have no slip the however the TCC seems to drop pressure under light load despite the setting on the offset to max, it's like there is a missing parameter that forces the TCC pressure to reduce until slip occurs, like 02 hysteresis. its probably an economy setting to reduce pump pressure but it makes the TCC drop out and grab cyclically at low load.

    Probably should have thought of it before, reducing the adaptive minimum to zero has helped considerably.

  8. #8
    Look at your tcc apply ramp chart as well. I will let you know when I log next but I suspect that even if you command 0 slip, it will gradually lower pressure until it slips and then ramp up pressure according to this ramp chart. Fuel economy increase of milligrams of fuel from the reduced engine load.......pffft. The tcc regulator offset affects holding pressure as well, but it seems to be that the total holding pressure is the tcc regulator offset + the tcc apply ramp pressure at zero slip. Then it will increase pressure with slip at the rate allowed by the chart, which is at a pretty wimpy rate.

    IMO you really want to stop regular tcc slip, as it will put clutch material in the system and start mucking up the valve body, then all hell breaks loose. I am not even allowing it in any gear but 5 and 6, stock cal allowed it in 3 and 4 at like 22 mph or some ridiculous thing. It would also help to not let it apply at higher throttle points, especially with mods.

  9. #9
    Quote Originally Posted by NotSure View Post
    Look at your tcc apply ramp chart as well. I will let you know when I log next but I suspect that even if you command 0 slip, it will gradually lower pressure until it slips and then ramp up pressure according to this ramp chart. Fuel economy increase of milligrams of fuel from the reduced engine load.......pffft. The tcc regulator offset affects holding pressure as well, but it seems to be that the total holding pressure is the tcc regulator offset + the tcc apply ramp pressure at zero slip. Then it will increase pressure with slip at the rate allowed by the chart, which is at a pretty wimpy rate.

    IMO you really want to stop regular tcc slip, as it will put clutch material in the system and start mucking up the valve body, then all hell breaks loose. I am not even allowing it in any gear but 5 and 6, stock cal allowed it in 3 and 4 at like 22 mph or some ridiculous thing. It would also help to not let it apply at higher throttle points, especially with mods.
    The TCC apply ramp does not stop the pressure dropping until slip occurs, so far so good on the minimum adaptive though.

  10. #10
    Well I cannot figure out where it is getting the apply/hold pressure from. Mine is applying at 35 psi, and then if it slips it will ramp up. But as soon as the slip is gone it starts slowly decreasing. I changed the regulator offset from 180 to 360, 0 for the Min adapt and put 500 kpa in the Max adapt, and got aggressive on the apply ramp, even with 150 kpa at 0 slip column, stepping up from there. What am I missing? If it takes 50 psi to keep it locked, for example, then I want it to stay at 50 psi whenever it is applied.

  11. #11
    Quote Originally Posted by 4wheelinls1 View Post
    The TCC apply ramp does not stop the pressure dropping until slip occurs, so far so good on the minimum adaptive though.
    Is your TCC Adapt functional per the torque min/max? My stock cal has Torque Max at 30 lb/ft, Torque Min at 0. It is basically disabled. Idle in gear it takes like 50 lb/ft. I looked at a CTS-V and a ZL1 cal and they are completely disabled by setting the torque min at 22 lb and the torque max at 15 lb.

  12. #12
    Well I just tried enabling TCC Adapt by raising the torque max limit, and then putting in 180 kpa to the Cell Preloads, thinking it would start there. It did not. This is with the Adapt Min at 0 and the Adapt Max at 250. Regulator Offset back to stock at 184, and apply rate at 4x stock. It tries to apply with 18 psi and then ramps up until it holds, then ramps down until it slips.

  13. #13
    Update, I don't know where the true/final apply numbers are coming from, but I did get the apply pressure up to where it won't slip. The regulator offset does not match commanded though. At stock 184 kpa it is showing 18 psi on the scanner (should be 26). At 360 kpa it is about 35 psi (should be 52). At 600 kpa it is 58 psi (should be 87). But it doesn't seem to be dropping back off until it begins to slip anymore.

  14. #14
    Tuner in Training
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    May 2016
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    Just some helpful info from my experiences:

    If you have a factory converter (at least this was the case on my 2013 C6), it is designed to "slip" a few RPM without any ill effects. I believe it is a special spun/woven carbon material designed for the best of all worlds; very few manufacturers make these clutches in popular aftermarket sized. More accurately, if/when you install an aftermarket single-disk converter in one of these cars (definitely depends on year), you will not be able to achieve 0 slip and will ruin the clutch very rapidly. I went to a triple-disk carbon fiber clutch after my first aftermarket converter died.. I can lock at 25 mph in 3rd (1200 RPM) and stay locked through 6th with zero issues. I also have it engage lock at 105 in 3rd at WOT with zero slip and it totally transforms the car in the top end.

    BTW: the shuddering described here can PROBABLY be solved by playing with your fueling/timing/DFCO tables. I have found that part throttle shudder in my car is either too much or too little timing, or I am transitioning in/out of DFCO rapidly. In any case, the shudder is caused by discontinuities in the torque provided by the engine, and the locked converter clutch allows these to be felt by the driver.

    I personally haven't understood people who don't lock the converter down low in 3rd and up, but I also have 350 lb-ft at 2000 RPM in a 2800 lb car.