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GMC transmission issues

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  • Dakota Boy
    • Jun 30 2009
    • 1561

    GMC transmission issues

    4L60E trans in a 1996 Sonoma (4X4). 135,000 miles on it. Trans fluid and filter changed at 50K, 100K and again a month or so ago....

    Issue = it makes a whining/mechanical noise. Usually starts doing this during freeway driving. Then the next day, while driving in town, it's quiet.
    Transmission fluid now has black/brown specks (not metal) in it.

    Somebody at work here says if I remove it and take it to Cottman, they'll rebuild it for like $450.

    This would be the first time I've had a vehicle experience tranny problems, and I dont really feel like getting "robbed" so to speak.

    Any guidance from you veterans would be greatly appreciated.
  • tbird430
    • Jun 18 2007
    • 2648

    I'd try flushing it one more time & going back with GM's new Mercon VI. It is compatible with the old Mercon fluid & mixable too.

    Add an entire can of the Sea Foam brand trans conditioner to this tranny before you "top it" back off too. Drive it a few miles (100), then repost back to us.

    Finally, does this trucks transfer case run that special "BLUE" GM synthetic fluid or regular Mercon transmission fluid.

    -Jon in TX.
    Last edited by tbird430; June 14, 2010, 02:09 PM.
    The 1960 Ford Thunderbird. The WORLD'S most wanted car....

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    • simplyconnected
      • May 26 2009
      • 8772

      If you ever need your trans overhauled, save yourself a bundle by bringing the trans in by itself.

      The transmission shop ties up a hoist and a mechanic for removal and installation. What about the time in between? Either your car ties up the hoist until your trans is rebuilt on the bench, or they lower and push your tranny-less car out into the lot (and push it back again when your trans is ready).

      So, ask your transmission shop how much they want to overhaul your bare transmission.
      Member, Sons of the American Revolution

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      • Dakota Boy
        • Jun 30 2009
        • 1561

        Both the AT and transfer case call for Dextron III.

        I'm sure I'll be removing the trans myself here very soon. I'll chalk it up as a learning experience, since I've never removed a transmission.

        I bought new tires for the 'Bird yesterday to replace the 30(?) year-old MT Indy Profiles. Cooper Cobra radials.... Anyways, the tire shop was a small place run by a guy who's been in the area for all of his 60+ years. He recommended a couple transmission shops. He also said I should stay far, far away from any of the "chain" type shops.