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Thread: WOT TCC Lock 8L90E

  1. #1
    Tuning Addict WS6FirebirdTA00's Avatar
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    WOT TCC Lock 8L90E

    All - I have been trying to read, but haven't come across any good applicable threads for my question.

    I have read mixed comments on TCC lock for WOT.

    Here is my stock WOT TCC lock "normal" lock. 2018 Sierra 5.3L 8L90E

    WOT TCC.PNG

    WOT runs it will lock on me and I am trying to figure out if that is good or bad. From what I see, many say do not lock at WOT. I am wondering why the factory tune allows it. What are the benefits and risks? Ultimately I am looking to see if I should disable.

    I get what I feel is a slight shake on hard accel and I have not been able to pinpoint it. I *think* it happens in 2nd, which led me to this question. I am wondering if the TCC lock is causing that sensation. It almost has a slight imbalance feel to something when that happens. I am going to try to tie it to RPM, speed or gear.
    2000 WS6 M6 (motorless)
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  2. #2
    Potential Tuner
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    Two things come to mind;
    1. GM program some sort of a slip in the TCC to counteract the engine firing pulses - really? Who notices those things
    2. GM had issues with TCC chatter and supposedly fixed it with a new type of tranny oil replacement.
    I am placing the same motor in a Jeep Wrangler from a 2016 Sierra. I will be installing the new synthetic oil and see what happens. And if I can I will disconnect that pulsy thing. Give me a break GM.

  3. #3
    Tuning Addict WS6FirebirdTA00's Avatar
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    I have set TCC slip to 0 in most cruising areas.

    Also, I put the new fluid in mine after doing a B&M pan and a few flushes.

    I think the sensation I am feeling is linked to when the TCC starts to apply during WOT lockup. The following gear always feels fine, just when it is going from high slip to little slip. That is just what I think at this point, happens in 2nd a lot now thinking about my pulls. That is the first gear it allows WOT lock.

    Most things I read people say don't lock WOT. If locked at WOT, people have lost time and MPH. Just curious if it is the same here, looking for risks/rewards.
    2000 WS6 M6 (motorless)
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  4. #4
    Advanced Tuner
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    I think you are probably correct in that you are feeling the tcc apply ramp. A slip then catch scenario that can translate to vibration in the seat.

    At the drag strip in my c7 I tested stock lockup and then just locking up in 5th to minimize rpm drop and the car ran very consistently no matter how I had it set as even when it was unlocked it was at 98% efficiency. I think honestly it's fair to do whatever is most comfortable. You'll more than likely notice that feeling less locking up in a higher gear.

  5. #5
    Tuner in Training Mbrowning's Avatar
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    The factory set them up to lock at wot because they have tcc torque limits in place. I would be willing to bet yours is disabled. You will probably end up with a better et. and happier transmission if you disable wot lock. Let us know what you come up with. I'm just starting to see 8 speeds at my shop.
    Browning Performance

  6. #6
    Tuning Addict WS6FirebirdTA00's Avatar
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    I have all factory TM enabled still. The only thing I changed for torque limits were the gears in the ECM calibration that limited throttle.

    I tried some unlocked tests, it is slower by several tenths in a 2nd gear pull. Unlocked feels good to start, but ends weak. Trying to lock up at peak torque leads to an early lock point to basically match the stock settings. If it locked at the commanded RPM immediately, I could see a benefit. You have to command too early which pushes the unlock speed pretty low.
    2000 WS6 M6 (motorless)
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  7. #7
    Tuner in Training
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    8 speed will always pull harder with the converter locked at WOT. What I do is disable TCC lockup part throttle until 8th gear at 55 mph, but leave the WOT lockup alone. Trans is much smoother this way. The caveat is a slight loss in fuel mileage. Also, instead of zeroing out the TCC slip tables, I tried reducing them by 70%. I have noticed It allows a smoother downshift this way.
    Last edited by 1scls1z; 2 Weeks Ago at 12:45 PM.

  8. #8
    Tuning Addict WS6FirebirdTA00's Avatar
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    I still have mine locked at cruising speeds. I tweaked a few speeds and the apply pressure and really love how it shifts and drives. It is amazing what GM didn’t do from the factory, could have a completely different reputation.

    I set min TCC slip to 3 RPM to match the AC min since we can’t modify that value.
    2000 WS6 M6 (motorless)
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  9. #9
    Advanced Tuner mbray01's Avatar
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    IN OLDER TRANSMISSIONS LOCKUP WAS DISABLED BECAUSE OF THE LARGER RPM DROPS BETWEEN GEARS(TORQUE LOSS FROM DROP) WITH THESE CLOSE RATIO GEARS THEY PERFORM BETTER LOCKED. i HAVE NOTICED ET DROPS, AND HP DROPS WITH THEM UNLOCKED. NOW THIS IS WITH THE STOCK CONVERTER OF COURSE. LOOSE AFTERMARKET CONVERTERS ARE A TAD DIFFERENT, THEY PILL PICK UP UNLOCKED, BUT YOU HAVE TO PAY VERY CLOSE ATTENTION TO SHIFT SPEEDS
    Michael Bray
    Rusty Knuckle Garage
    Slidell, Louisiana
    15yr Master Tech.
    Custom Car Fabrication, Customization, High Performance.
    GM World Class Technician
    Shop Owner

  10. #10
    Tuning Addict WS6FirebirdTA00's Avatar
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    Good point on the gear ratios, thanks!
    2000 WS6 M6 (motorless)
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB