2008 Yukon Denali Transmission Swap

Discussion in 'Engine & Drivetrain' started by ford141, Jan 14, 2020.

  1. thompsoj22

    thompsoj22 Full Access Member

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    ivs got the same vehicle at 139k miles. trans is still working great but when it starts acting up i intend on rebuilding it myself for approx $2,500 and that will include a new converter/tehcm. The 6L80E is really a rebuilders dream as they are somewhat simple. Just my opinion but dropping the tehcm and installing the "films" on the solenoids is a good idea if you were going to rebuild the trans but not as a cure for your issues. spend the hundred on a "trusted" diagnosis from a "hundreds of good reviews" trans shop. does it act any differently stone cold as opposed to op temp? the shop can diagnose faults/pump pressure but not the cracked/leaking drum which would require the teardown. junkyard trans, unknown condition. your trans has survived 175k miles and still going. i would opt for the rebuild with a solid warranty. anyway, it is no fun to have to deal with major repairs when cash is tight! hang in there.
     
    Last edited: Jan 17, 2020
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  2. ford141

    ford141 Member

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    I agree that rebuilding is the best route, and I'd love to do it myself (did the C6 in my street truck 10 years ago, still working great), but I don't have the time to do that with this Yukon since it's my daily. I also don't know of any reputable trans shops around here anymore, most of them have went out of business years ago. I did have the local GM dealer look at it a few years ago for a rough downshift issue that it has always had, and they retuned the software which helped but did not cure the problem. Still to this day (and for the last 50K miles of ownership) it likes to stay locked in 6th when you start up a hill and will start lugging the motor and loosing speed while you roll into the throttle. After loosing some speed, the transmission with abruptly downshift to 4th, which jolts the drivetrain and shakes the whole truck. Doesn't do it all the time, but just when you think it won't, it willl. Never any codes.

    As far as the slow 4-5 shift that has just started, it only happens in the morning when the trans is still cold. Usually the trans temp is between 80-100F degrees by that part in my commute. I don't notice it after the trans warms up (although in cold weather it never goes above 120F).
     
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  3. Big Mama

    Big Mama Full Access Member

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    Eric, does it do the same thing if you shift manually?
     
  4. ford141

    ford141 Member

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    Yes it does. I have started shifting manually when I leave in the morning so I can leave it in 4th until I crest the top of the hill and the load lightens. Then I shift into 5th on the downhill. The shift is still delayed but it's easier on the clutches when it finally catches.
     
  5. tgui

    tgui Full Access Member

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  6. Derick

    Derick Full Access Member

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    Look up.
    See if you can find a donor truck or van....grab the trans out of it and sell the remainder as a parts vehicle. Might get your money back.

    WatchJRGo did that to get a 4l80e that hes putting in this rolls....
     
  7. thompsoj22

    thompsoj22 Full Access Member

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    Now im just guessing, Ill say your converter is failing, If im not mistaken the converter should "unlock" as the rpm drop when climbing, this is a function of the converter and requires no electronics it is simply rpm/load related. you will notice a slight increrase in rpm as it unlocks, if the "lug/hill" continues the computer will initiate a downshift.your converter dosent seem to be unlocking by your decription? If you do the solenoid films you will be removing the tehcm from the trans, there is a filter associated with the tehcm, there maybe debris there causing shift problems. imo your shift problems should be worse as the trans fluid gets to op temp? get back with your results as the info you provide helps others when it is their turn.
     
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