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Thread: No FWD Gears ? Fresh LS/4L80E Swap

  1. #1
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    No FWD Gears ? Fresh LS/4L80E Swap

    I recently finished a C10 Build w/ the below details. The observable symptom is that the Wheels will turn in any FWD gear when truck is on jack stands. When on the ground, the truck will NOT move in any FWD Gears, so it appears the trans is slipping. Reverse functions normally w/out issue. When unplugging the Round Connector to the Transmission (if I understand correctly this defaults trans to 2nd gear), the observable symptoms are the same? still will not move in FWD. W/ round connector connected, I can manually engage all 4 gears via the HPTuners Scanner, and hear the Solenoids Operating (no solenoid engagement in 2nd). Additionally I can hear the TC Solenoid engaging when activating through the software. I have confirmed that the transmission level is correct (using stock dipstick).

    Engine ? 2001 6.0L LQ4 (2001 Silverado)

    ECU ? 2002 4.8L 4L60E (OS 12212156) ? Custom 3 Bar OS has been installed due to this being a Turbo?d application.

    Trans ? 2000-2001 4L80E w/ TransGo HD2 Shift Kit installed by myself (Trans came from friend of a friend, and was sold as is, but was not know to have any issues and was a pullout from a local salvage yard)

    Shifter ? Lokar Tunnel Mounted w/ Mechanical Linkage (rod and heim). PRNDL position working correctly when shifting, as viewed through HPTuners Scanner as detenting through positions of shifter.

    Tuning Process ? I did NOT do a Segment Swap. Rather I did a Comparison Log through the HPTuners Software, comparing against the 2001 6.0L 4l80E Software (OS12208322), for which would be appropriate for the 4L80E Transmission. I applied the differences for the Transmission folder/section of the software. In reading multiple posts/literature, I was hesitant to pursue the Segment Swap, and demised that applying the Compare differences was essentially doing the same thing.

    Codes Present ?
    - P0740 - Torque Converter Clutch Circuit Malfunction
    - P0785 - Shift/Timing Solenoid DTC Trouble Code

    My Questions Are:
    - Is a Segment Swap still required, considering I updated the software using the Compare features to update all parameters from the 4L60E to the 4L80E?
    - W/ the two codes that are present, is it apparent to anyone what my issue is?
    - By unplugging the round connector and w/ the observable of wheel spin on the jack stands in fwd and none on the ground, have I confirmed that this is a mechanical problem and the trans will need to come out?
    - Is a pressure test suggested as the next step in diagnosing the issue? IF so, does anyone have a guide/recommendation on going about this. If I understand correctly there is a port in the Drivers Side that I will plumb a gauge to check pressure in each gear? Low Pressure would indicate a leak from a sealing ring or clutch pack, etc?

    Ive been working on this Turbo C10 build for about 7 years now, and was excited to take the truck for its first drive this past weekend. I was quickly discouraged to find that FWD gears weren?t working. Any help/advice from the group would be very much appreciated.

  2. #2
    Tuning Addict 5FDP's Avatar
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    A segment swap is still required, copy/paste will not work.

    It should still engage the transmission even if the segment swap wasn't done first. You also must do the segment swap with the stock OS, then apply your 3 bar OS to that file.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
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    Quote Originally Posted by 5FDP View Post
    A segment swap is still required, copy/paste will not work.

    It should still engage the transmission even if the segment swap wasn't done first. You also must do the segment swap with the stock OS, then apply your 3 bar OS to that file.
    Thank you for the information. I appreciate it.

    Since I have the 3Bar OS currently programmed, how do I proceed? For example... do I program back to the original OS Containing the Segment Swap using a "Write Entire" and then Program the 3Bar OS back in after that using a Write Entire again? My understanding is that a Write Entire is required anytime changing the OS... if Im correct, when going back to the originall cal that was in the controller, I will be changing OS, and then when programming the 3Bar OS, Ill again be changing the OS. I know there are risks of programming using Write Entire... so I just wanted to make sure I get the procedure and sequence correct before doing so. Also.. Im assuming this wont cost me any credits since I have writes to that original calibration/vin?

    Thanks again.

    ANDY

  4. #4
    Tuning Addict 5FDP's Avatar
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    Correct, it won't cost you anything because you have the stock file already licensed.

    Flashing back to stock is the way to do it. Do that first with a write entire. Then take the stock file and find a 4L80e to segment swap with, complete that and then apply the 3 bar OS back to that file. Then write entire the 3 bar OS/4L80e segment swapped file in.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  5. #5
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    Quote Originally Posted by 5FDP View Post
    Correct, it won't cost you anything because you have the stock file already licensed.

    Flashing back to stock is the way to do it. Do that first with a write entire. Then take the stock file and find a 4L80e to segment swap with, complete that and then apply the 3 bar OS back to that file. Then write entire the 3 bar OS/4L80e segment swapped file in.
    That worked for me. Programmed successfully, and no DTCs related to the trans. Still no go in FWD gears, so I will be checking pressure and guessing will likely be pulling trans. But now I know my programming is correct and in no way related to my issues. I sure appreciate your help. THANKS

  6. #6
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    With the transmission main connector unplugged (no 12V power) the 4L80e will default to 2nd gear. It should apply and pull in forward and reverse both.

  7. #7
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    Did you seat the converter correctly? It sounds like a pump issue.

  8. #8
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    By doing a segment swap, I was able to resolve all Trans related DTCs. Again, on jack stands I get forward wheel movement in Drive, but on the ground there is not enough there to power/move the truck forward. On the brake, Reverse holds strong and seems normal.

    In regards to the question from DougO on the converter.. I guess I assumed that "seating" the converter was pretty standard. Ive done this many times on TH400 but this is my first 4L80E. The converter seemed to install/engage fine, and it bolted up to the flexplate fine as well. Is/Was there something else I should of been paying attention to here?

    I installed a gauge to complete a pressure test and below were my results.

    Drive Idle - 90 psi
    Neutral Idle - 100 psi
    Park Idle - 100 psi
    Reverse Idle - 135 psi

    Drive High Idle - 150 psi
    Neutral High Idle - 110 psi
    Park High Idle - 130 psi
    Reverse High Idle - 180 psi

    Observable Symptom - I did this testing w/ truck on jack stands. I am getting forward wheel movement when in Neutral Position. I confirmed this both w/ and w/out the shifter linkage attached, to rule out any issues w/ the shifter linkage. Again, the PRNDL status shows the correct gear when selecting all positions/gears w/ the shifter.

    As mentioned before, I did install the TransGo HD2 Shift Kit prior to installing this transmission. Im fairly competent (id like to think) and took my time installing and really had no questions/issue when installing.

    Is it possible my pressure and observable symptoms could have something to do w/ that shift kit install, or are the symptoms indicative of something else? Where would you suggest I go next in trying to diagnose my issue.

    THANKS ANDY

  9. #9
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    Check the c clip on the booster valve. It might have slipped out of the groove. It may sound stupid but it has happened to me before