draining trans fluid 4T80E
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Northstar Engines and System Technical Discussion Discussion, draining trans fluid 4T80E in Cadillac Engine Technical Discussion; my trans is going out on me (4T80E pump whining causing some slippage) and the fluid is pretty nasty. i ...
  1. #1
    bbrewer5 is offline Cadillac Owners Member
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    draining trans fluid 4T80E

    my trans is going out on me (4T80E pump whining causing some slippage) and the fluid is pretty nasty. i put some lucas stop slip in it and it made worlds of difference so i think i would like to COMPLETELY drain and refill the trans with new fluid so i can make this thing last as long as possible. (wont be able to replace it until sometime in july.) i know flushes are bad, so im not going that route, and i know some people have disconnected trans lines and poured in new fluid while the old pumps out. my question is, what would be the easiest way to get ALL of the fluid out of my trans and not just the 6 quarts that come out with a pan drop? if its the disconnecting line method, where would be the easiest (and safest) way to acomplish this? my car is a 1997 eldorado ETC.

    thanks for any and all help,
    Brian

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    JimD is offline Cadillac Owners Connoisseur
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    Re: draining trans fluid 4T80E

    I disconnect the line at the top of the radiator side tank and adapt whatever brass fitting is needed into the radiator threads. Attach a hose long enough to reach to the driver's door and have a 5 gallon bucket available.

    Idle engine until fluid stops flowing and immediately stop the engine. Pour in a case of Dexron III or Dexron VI and adjust the level as needed.

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: draining trans fluid 4T80E

    Make up a drain hose which will run from the radiator transmission oil cooler outlet to a drywall mud bucket (5 gallons or so). Go through the 20 quart exchange process. Not difficult, but make very sure you understand that the 4T80E is a dry sump transmission, so you have to be a bit careful to correctly fill after flushing. NO OIL will show on the dipstick with engine off.

    There are several threads on the process in here and Tech Tips and Northstar over the past 6 months. Someone just did it a week or so ago.

    ......or look for a late spring special at a GM dealer and have them do it with the new DEXRON VI synthetic. Their machines do the whole enchilada.

    Either way, with oil pricing what it is, it ain't gonna be cheap.

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    bbrewer5 is offline Cadillac Owners Member
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    Re: draining trans fluid 4T80E

    EDIT* (posted at the same time as submariner lol)

    ok i know this is one of the metal lines but which side? standing in front of the car looking down at the engine should it be on the left side (battery/surge tank side) or the other?
    will the flow be coming from the radiator or the disconnected line?

    thanks alot,
    Brian

    EDIT 2* almost forgot, ive read the topics in the past (did search but could find anything), and i thought i recalled reading that you should pour the new in as the old pumps out? or should i follow JimD's advice by letting it all drain out and then refilling it? like you said its a dry sump, i thought filling with engine off was a no-no on a dry sump...

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    JimD is offline Cadillac Owners Connoisseur
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    Re: draining trans fluid 4T80E

    Quote Originally Posted by bbrewer5 View Post
    so the fluid will flow from the radiator or from the tubing that runs into it?
    From the radiator

    what kind of pressure should i be expecting?
    I have no idea.

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    tateos is offline Cadillac Owners Connoisseur
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    Re: draining trans fluid 4T80E

    I think you should save the money you will spend on this process and put it toward the new tranny

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    bbrewer5 is offline Cadillac Owners Member
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    Re: draining trans fluid 4T80E

    Quote Originally Posted by tateos View Post
    I think you should save the money you will spend on this process and put it toward the new tranny
    40 bucks? i already bought the 20 quarts and cost me just under 43 bucks, im pulling money out of my car loan for the tranny and will have to make much bigger payments for a few months. thanks for the recommendation though.

    like i said if the lucas stuff made that big of a difference, im sure this will too as the fluid looks very dark (brownish almost like used motor oil) and smells burnt.

    something ive been searching all over for and absolutly can not find (even though ive seen it here before) is which line do i need to remove, there are metal lines on both sides of the radiator, which one is it?

    Thanks again.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: draining trans fluid 4T80E

    The metal lines on the driver's side of the radiator are the transmission cooler lines. Double check their destination with a flashlight. Generally, the bottom line is the return line to the transmission, there's practically no pressure drop across the cooler at idle, so you're not fooling with high pressure oil. There are both pipe thread and quick-connect fittings involved, so you may need a set of fittings or O-rings to prevent leaks upon reassembly.

    You might be well advised to get a real GM Factory Service Manual from www.helminc.com , or try eBay.

  10. #9
    bbrewer5 is offline Cadillac Owners Member
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    Re: draining trans fluid 4T80E

    Quote Originally Posted by submariner409 View Post
    The metal lines on the driver's side of the radiator are the transmission cooler lines. Double check their destination with a flashlight. Generally, the bottom line is the return line to the transmission, there's practically no pressure drop across the cooler at idle, so you're not fooling with high pressure oil. There are both pipe thread and quick-connect fittings involved, so you may need a set of fittings or O-rings to prevent leaks upon reassembly.

    You might be well advised to get a real GM Factory Service Manual from www.helminc.com , or try eBay.
    it ended up being the top line that is the return line, i got my airbox removed and everything and had a makeshift hose hooked to it but it is in fact pressurized even at idle, im guessing 20psi or so because when the hose shot off the fluid shot in a horizontal line...now i have to put it all back together and buy a real fitting and since sizes on stuff like this are virtually impossible to find out except for trial and error, im gonna wind up buying 5 different size fittings....this car loves to anger me every time i work on it, never had that problem with previous cars....

    anyone happen to know the thread size of the return line?

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    bbrewer5 is offline Cadillac Owners Member
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    Re: draining trans fluid 4T80E

    Well i completed the job without having to buy a hose, i just disconnected the inbound line at the bottom and angled it down into an oil pan instead and blew out the cooler with an air compressor.

    I am amazed at how much better it runs, i expected a little improvement but jeez, it runs like there is nothing wrong with it now. i got my lost fuel economy back too. (was getting about 13-14mpg, now back at 17-19 city) im positive that damage has already been dealt and i know i will still wind up having to replace it but i think i just bought myself a few thousand more miles.

    Thanks for all the help guys ...great site, full of knowledge

  12. #11
    JimD is offline Cadillac Owners Connoisseur
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    Re: draining trans fluid 4T80E

    Well done on your pragmatic approach. Messy, but well done.

    You might have bought more miles than you are thinking. Pay attention to the color and aroma of the transmission fluid for the next 1,000 to 3,000 miles. Another drain and refill might be worth doing.

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