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  1. #1

    Default Size and threading of the transmission cooler lines

    I'm still on my kick of fixing/improving my transmission on the truck. Up next is replacing the stock cooler and lines for an aftermarket cooler. I do not intend to use the existing factory cooler lines because they are leaking pretty good at the transmission. The issue is that I could not get the top cooler line straight when I went to screw the fitting into the adaper on the body of the case. So, I want to replace all the steel line with flexible hose all the way up to the aux cooler that I bought and haven't installed yet. So, in the end, what size and threading are the transmission cooler line fittings at the transmission. Also, if I pull the "adapter" off the case, can I get more flow out of the cooler? If so, what size and threading are the threads in the case of the side of the transmission. The transmission is a TH700R4/4L60 (NOT 4L60E, if that makes a difference)

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 265K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half

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  2. #2


    After some quick googling, it looks like the case has 1/4" pipe threads. After a run over to Home Depot, I found a couple of 1/4" to 1/4" barb fittings. Well, I checked the fit of the barb fitting to the diameter of hose that came with the cooler, and of course the barb fitting is too small. I should have gone with the 1/4" pipe thread to 3/8" barb fitting, but that'll be another trip... Before I make a second mistake, can anyone confirm that the transmission case does have 1/4" pipe threads? Maybe Mike, the King of Remote Filters...

  3. #3


    the 4 speed auto has a few different names but i came across this information.
    "Transmission fluid cooler lines: on the 700R4 the bottom fitting on the right side of the transmission is the "out" line to the cooler and the top fitting is for the return line from the cooler. These fittings are 1/4-inch pipe thread, and CAN include an adapter from the factory for threaded steel lines in an SAE size."

    i hope this helps..........but, i use braided lines or run steel as the main line and the rubber flex lines at both ends.... (i add the filter and temp probe up front where it is easy to swap out the filter. there normally is a ton of space between the grill and condensor...............mike
    Michael Collins
    1993 4X4 Suburban
    many other toys as well

  4. #4


    I was thinking about doing something similar to you with the hard or steel line for the main run, but I thought it would be better and easier in the long run to run the rubber flex the entire way so it's one contiguous piece with no joints to leak and cause grief. How did you set up your temp sender in the front, a T fitting of sorts? Thanks Mike

    EDIT: Also, what type of outboard filter do you use, a can-style filter or what? To prolong the life of this thing, I may add in a second filter too...

  5. #5


    i get the remote can filters systems. they have 1-2 ports on the top so you can put temp or pressure sensors. just make sure you are on the output side of the tranny.
    i found you can take a non temp port one and drill and tap it so you can add a sensor easy.....mike

  6. #6


    I'm sold My only question with the filter is does it take pretty much any old can oil filter from the auto parts store, or is it a special filter for transmissions that has to be special ordered or something? It also solves my temp sender placement issue/question. Having the sender way out there doesn't skew the temp reading? I think I'm going to pull transmission pressure off the test port on the side of the transmission, since that test port SHOULD be right off the pump (right???)

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