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Lower transmission line leak at radiator bolt: trick to tighten and seal?

5237 Views 7 Replies 6 Participants Last post by  khomer2
I replaced repaired radiator into 1998 C280. Tightened upper Transmission line Banjo Bolt with no issues. No leaking under pressure. Since the line going into the lower radiator transmission cooler port is a flared fitting, I've tightened it up as tight as it can go, but I'm still experiencing a tiny drip, when she's under pressure. Is there a trick to tightening it to prevent a leakage?
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Patman1, I am so very sorry that I didn't revisit this thread. A year, plus, is inexcusable, and I apologize, but I still could use the help. I didn't receive a notification that a reply had been posted.

When I disconnect the lower transmission hose from the radiator connection, a small amount comes out. (I work on a slight incline in my driveway, and go down where the radiator shroud would be. I remove the shroud to work on that line.) I'd estimate it to be a couple of cups, 6 - 8 oz.

My solution, in Sept 2017, was to slather the back of the fitting/collar-nut, and the metal of the hose with Black Ultra RTF sealant. It created a seal from where the drip was occurring. It stopped the leak for about a year.

I noticed the drip occurring again, last week (Dec 2018). I removed the shroud, cleaned old Black Ultra RTF sealant off the fitting, and loosened the fitting/collar-nut. I pulled off the nut/collar, and waited for as much ATF to drain out as I could. It looked like some of the end of the radiator fitting was crushed, like a cross-threading had occurred. I was told, once to put on Teflon Tape, as used in plumbing applications to help seal it. I tried to apply the tape, but had difficulties, yet ended up with at least one wrapping of it along the radiator connection. I reattached the nut/collar, paying attention to how 'direct/straight' the fitting was. I tightened it as tight as I could, and again, slathered the nut/collar end-closest-to-the-transmission with the Black Ultra RTF. It has, still, a small drip, but not massive, and I don't see it on my driveway, yet, but have seen some along the bottom rubber radiator hose.

Is there supposed to be a rubber seal/o-ring at the back of that nut/collar to help seal that?

Thank you for your help, Patman1.
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I put the teflon tape on the male extension from the radiator. I don't believe that there is an O-ring on the inside of the nut. It's like a brake line compression fitting, but the transmission line which 'mates' to that male extension is pressed onto the mating surface of the threaded radiator piece that sticks out from the radiator. I've not been under the C280 since the repair, and I've not seen any drips on driveway since I've done it. Thanks for your advice on the teflon tape. I'll check it out, further, though.
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