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Thread: Built 4L60E Issues, Desperate for help!

  1. #1
    Potential Tuner fleshe's Avatar
    Join Date
    Aug 2018
    Wichita, Kansas

    Built 4L60E Issues, Desperate for help!


    I've got a fairly decent 4L60e build that I'm starting to have some issues with and I'm hoping to get some guidance with my issue from the combined intelligence on this forum.

    Build List

    2007 Chevy Tahoe, 5.3L Gen 4 Iron Block, BTR Stage 4 Cam, Long Tube headers, Coated Pistons, CAI
    E38 PCM / T42 TCM

    Engine Dyno tuned to 330 HP NA

    Corvette 2nd Gear Servo
    Beast Sunshell
    Billet 10 Vane Pump Rotor
    Sonnax Boost Valve
    Billet 4th Gear Servo
    TransGo Performance Separator Plate
    Circle-D HP 278MM 3200s Converter
    Derale 15800 Electra-Cool Cooler
    Heavy Duty 3-4 Clutch Pack
    Anchor 2638 Transmission Mount

    My issues started last week and the build has only been running for about a month now behind a 330 HP dyno tuned N/A 5.3 Gen 4 motor. The transmission has been tuned using BlueCats Tuning tool.

    When the transmission is cold, I put it into (D) and all is well under part throttle until it tries to shift into 2nd gear. During the shift there is a loud and violent bang followed by my RPMs shooting up like the transmission shifted into neutral. As the vehicle coast forward and the RPMs fall back down there is another bang like the transmission threw itself back into 1st and then it's like the transmission is permanently in neutral while the shift selector is in the (D) position. At this point (D) does nothing, if I manually put it into 1st gear, the car moves forward just fine and I can manually shift all the way to 3rd just fine. While in 3rd gear the transmission will not go into lock up and if I shift into (D) to hopefully go into 4th aka OD, it acts like its in neutral.

    Now, here's the weird part. If I drive around in 3rd for about 5-10 minutes, it i will eventually go into overdrive and I can put the truck back into (D) and it will shift just fine on its own through all the gears and even lock the converted like there is nothing wrong. It will operate just fine until I let it sit long enough for the transmission to cool down and then it starts this entire process all over again.

    What are your thoughts?

    Things I've tried

    1. Flushed transmission fluid and put in all new fluid (the old fluid was discolored but not toasted by any means)
    2. Check shift cable to make sure it was in the proper position (all looks good)
    3. Reloaded the Tuned TCM calibrations and even put the factory calibrations back in. (Both do the same)

    I'm at a loss and so is my transmission builder. At this point I think I may have a bad TCM.
    Last edited by fleshe; 06-16-2019 at 12:06 AM.

  2. #2
    Tuner in Training
    Join Date
    Dec 2018
    Central NC
    Sounds like you're going to be pulling the trans. Regardless of any electrical input, you'll always have forward and reverse drive engagement.
    If you completely unplug the connector from the trans you will get 3rd gear while in drive (and a hydraulic 3-2 downshift at full throttle), and reverse.
    If you have a complete neutral in drive, the trans is coming apart for diagnosis.

  3. #3
    You have broken the input sprag. Welcome to the world of 4L60E's.. Get used to pulling, repairing, and re-installing as it is going to be a routine you will become familiar with..

    Your list does not indicate what sprag you used during the rebuild. Borg Warner makes a dual-cage 26 element sprag that is supposed to be pretty good. I personally like the GM 4L65E sprags. They have plastic cages, but larger elements for better holding. Always replace ALL components sprag related. Do not put a new sprag up against old sprag races, or races with ANY damage, or discoloration. Putting a larger element sprag on a used, worn, sprag that had a smaller element sprag riding against it for 200,000 miles is just like putting a wide band, on a cupped reverse input drum-you are NOT going to have contact along the full length of the elements, or along the full width of the band..

    Good luck with your project..