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  1. #1

    Default 1993 K3500 4L80E help needed

    We have a 1993 ex cab 4x4 dually that was a 6.5TD/4l80E, and 4 yrs ago has a GM goodwrench rebuilt trans put in 3400 mi later the 6.5 broke the crank and sent a rod out of the block. With the bad economy we ended up putting in a 427 carb motor out of a C70 (rebuilt) and seeing we had the "updated" trans we axed the factory computor and put in a Bauman Optishift trans computor. As we also did a more or less frame up restore/repaint t it was Feb of 2012 before we put her back on the road.
    It funtioned perfectly for 6700 mi, untill 2 weeks ago when after being parked in the driveway for 2 days, reverse and 4th were gone. The optishift has several built in programs, and we used the 454 dually 4.10 gear settings from day 1. When it quit working we tried altering the shift points and line pressure was upped to 90% of max with no change.
    We then verified that all the speed sensors have proper waveform, is reading all the inputs and sending the proper signal and shift commands into the connector. Trans fluid is full but has a slightly burn smell but is still dark red and looks very clean. Also, the shift to 3rd is delayed at part throttle but on time and firmness at full throttle, and when you select reverse it feels like it's trying to engauge but not quite.
    Local trans shops wont do a diagnostic as the factory pcm is gone(no check engine codes), but will put in another rebuilt trans. Thanks in advance!

    Help Needed!

  2. #2


    Just a thought here, but have you checked out your shift solenoids? I don't know what the combinations are for that trans, but a bad shift solenoid can cause the loss of 2 gears if it's bad.
    Good Luck and God Bless
    Remember that if you're not part of the solution, then you're part of the problem!

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