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Thread: 6L80E shfting issue after start up

  1. #1
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    6L80E shfting issue after start up

    Hey guys,
    New here but I am having an issue with a 2011 LC9 with a 6L80E trans in a 1970 C10. (also I have HPtuners)
    I had the problem with the cracked piston(cant remember which one) so I contacted Mike at Century Transmission. I bought all the components from them to completely rebuild. I built it up as I will eventually put a cam and stuff in the future. I also put a circle D converter 3.2K stall. The problem I am having is that when I back out of my drive way and put in drive and pull out as soon as it is to shift from 1st to 2nd if bangs hard like it is going into reverse for a split second. Then you let off the gas pedal and it bangs again like its going into reverse just as its downshifting back to 1st. This only happens on the first shift after you start the truck. I cannot get it to do it until I shut the truck off for a minute, restart the truck and try to drive off. If I put in gear and slowly idle away and slowly give it fuel and let it shift it does not bang.
    Mike at Century told me that if it was a rebuild problem it would do it every time and so it has to be tuning.

    Does this sound right? does anyone have an idea?

    This is what I have done to date!
    Engine: Reset or verified the engine settings are all stock.

    Transmission: Reset all to 2011 Silverado 1500 settings
    I also tried 2010 Camaro trans setting as they are different but no change.

    I have logged pressure commands and see an ongoing spike in 3,4,5 in the log screen I can upload if need be when I get home from work!
    Please let me know your thoughts
    Thank you
    Scott

  2. #2
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    I forgot to ask if the DTC's or anything would change how the TCM monitors or verifies anything on first startup and first drive???

  3. #3
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    Anyone? Could this be a Clean/Learn Problem????

  4. #4
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    Yes it could be a clean and relearn issue as well as a TCM pressure switch issue.

  5. #5
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    Quote Originally Posted by DrLoch View Post
    Yes it could be a clean and relearn issue as well as a TCM pressure switch issue.
    Thank you for the reply
    Ok so pressure switch issue? What do you mean exactly?
    As far as the clean/relearn I have to figure out the brake pedal issue as the pcm times out as it reads no brake pedal depressed.

  6. #6
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    https://www.youtube.com/watch?v=ozVbzTvCZUA

    Pressure switches are bad. I had that on mine replaced TCM all was good. You need to fix the all the electrical issues before you get too carried away.

  7. #7
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    Quote Originally Posted by DrLoch View Post
    https://www.youtube.com/watch?v=ozVbzTvCZUA

    Pressure switches are bad. I had that on mine replaced TCM all was good. You need to fix the all the electrical issues before you get too carried away.
    Hey DrLoch
    I used this video to rebuild my tcm. I did the same as he did. Could I have done something wrong? The only electrical problem I may have is the brake light switch. Or trying to get the tcm to see it. I have heard it needs 12+ And 0 volts.
    Scott
    Last edited by First; 01-06-2019 at 06:55 PM.

  8. #8
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    I redid my TCM but it apparently had other bad issues as well. Got a reman from Dorman that fixed my issues. I know the procedure calls for the brake to applied, from that I'm assuming it has to detect that the brake switch is applied. I just looked at the TCM schematic for mine. Pin 6 is is for the stop lamp switch.

  9. #9
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    Quote Originally Posted by DrLoch View Post
    I redid my TCM but it apparently had other bad issues as well. Got a reman from Dorman that fixed my issues. I know the procedure calls for the brake to applied, from that I'm assuming it has to detect that the brake switch is applied. I just looked at the TCM schematic for mine. Pin 6 is is for the stop lamp switch.
    does it need a 12+ signal when brakes applied or ground when brakes applied???

  10. #10
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    609-002 is $420 from Autozone.... Damn!!!

  11. #11
    Senior Tuner mbray01's Avatar
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    who built it, from the sounds of it you did. one thing that has burned many guys building these transmissions as you have to pay attention to how snap rings are oriented. many in this trans have location lugs, that if the snap ring isnt installed correctly will allow the clutches to slip, or push into the next gear. most notably is the 1234 clutches, thy will push into the 3-5-R clutches, and will actually give you forward and reverse in commanded first gear. basically giving you an unintended line lock. also this isnt something you are really going to see on a common issues forum, as this isnt a trans problem but a builder problem. and what builder wants to admit they messed up?
    Michael Bray
    Rusty Knuckle Garage
    Slidell, Louisiana
    20yr Master Tech.
    Advanced Level Specialist
    Custom Car Fabrication, Customization, High Performance.
    GM World Class Technician
    Shop Owner

  12. #12
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    Quote Originally Posted by mbray01 View Post
    who built it, from the sounds of it you did. one thing that has burned many guys building these transmissions as you have to pay attention to how snap rings are oriented. many in this trans have location lugs, that if the snap ring isnt installed correctly will allow the clutches to slip, or push into the next gear. most notably is the 1234 clutches, thy will push into the 3-5-R clutches, and will actually give you forward and reverse in commanded first gear. basically giving you an unintended line lock. also this isnt something you are really going to see on a common issues forum, as this isnt a trans problem but a builder problem. and what builder wants to admit they messed up?
    Thank you for the post.... yes I did rebuild it and yes I was very careful with the orientations of the snap rings and the snap ring thicknesses. I used the feller gauges to make sure I had the correct clearances. Mike at Century transmission told me that if it was in the rebuild it would do it every time it down shifted back to first and started driving up through the gears again, but I only have a problem when I actually stop the truck put in park and shut off the ignition. Re-start the truck and drive off I have the problem..
    Mike told me that maybe I need to reflash the PCM/TCM by GM. He said sometimes files get corrupt and do weird stuff. That is the reason for me posting here.
    any help would be great! All this is helpful

  13. #13
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    you have a bind in 2nd is what it sounds like to me ...I own jasons custom transmission we build lots of 6l80s