Strange Issue After Trans Service

Discussion in 'Transmission & Driveline Topics' started by GoldenOne7710, Oct 10, 2019.

  1. GoldenOne7710

    GoldenOne7710 Equal Opportunity Offender Lifetime Gold Member

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    Recently did a simple pan drop and filter change on a 4L60E transmission. Ever since, it's been doing something I've never seen. Start engine, select drive and take off. Shifts smoothly and normally and has no issues....UNTIL you drive it for about 20 min. Then it starts shooting fluid from what appears to be around the front of the pan gasket. It's almost like there's an excessive pressure build up forcing fluid past the pan gasket.

    Pan bolts are tight. Even swapped the gasket a second time to make sure it was good. DOES NOT happen until its been driven for about 20 min. This thing operated perfectly fine until I serviced it. What would cause this after a routine, simple pan drop and filter change?

    Here are the steps I did...very routine. Done this a few dozen times over the years.

    1. Removed bolts, shifter cable bracket and dropped pan
    2. Pulled out old filter and pickup sleeve insert
    3. Cleaned pan and magnet
    4. Installed new pickup sleeve insert (tapped in with same diameter socket until it bottomed out in its bore)
    5. Installed new filter (pushed up until seated)
    6. Installed new gasket on pan, installed magnet to the same spot inside the pan and reinstalled pan
    7. Topped off fluid and road tested...rechecked fluid level...everything looks good. No leaks anywhere.

    There were zero issues removing or reinstalling anything. Could be pure coincidence this started when I serviced it? Even so...what would cause one to force fluid out after 20 min of normal driving?
     
  2. camaro71/holland

    camaro71/holland Veteran Member

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    My first thought is that you've topped off more than last time/normally and have a blocked/slipped expansion valve on top of the case. Once the oil comes to operating temperature, it wants to puke out the extensive oil and finds it's way through the gasket.

    I would drain half a quart and see what it does.
     
  3. GoldenOne7710

    GoldenOne7710 Equal Opportunity Offender Lifetime Gold Member

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    I actually have a theory now. I failed to mention this vehicle is 4WD. Here's what I believe happened. New fluid = slightly increased pressure. I'm thinking the output shaft seal has failed and fluid is passing through into the transfer case and overfilling it.

    The trasfer case has a vent tube that is routed over the top of the transmission and is situated right behind the engine. When the operating temperature rises from driving, the expansion of fluid is being forced through the vent hose. It likely isn't even the pan leaking...but coming from above and making it appear that the pan is leaking.

    If my theory is correct, confirmation will be easy. When I take out the fill plug for the transfer case...fluid should come gushing out if its overfilled due to intrusion from the transmission. I will check into it this weekend and post up what I found or didn't find.
     
  4. GoldenOne7710

    GoldenOne7710 Equal Opportunity Offender Lifetime Gold Member

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    Follow up. Removed fill plug on transfer case and had about 3 quarts of fluid come gushing out. Now I know what needs to be done. Now you know...if anybody else ever runs into this issue with a 4X4 trans.
     

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