Why are my Trans Cooler lines leaking?

[Chris4x4Gill2]

I had the TH350 out of my 72 rebuilt. New hard lines for the transmission cooler from Inline Tube used for re-installing. I cant get them to quit leaking from the fitting on the Transmission end.

Should there be a crush washer or seal installed? I though these were tapered pipe thread and would not require a sealant?

[chevy_mike]

I have always used some type of thread sealant on any pipe threaded items, otherwise I have had leaks (some more then others but almost always some weeping). With tread sealant, they haven't leaked.

[61K10]

Old or new fittings on the trans that the tubes attach to? Lines should be inverted flair that screw into the trans fittings. and no sealant needed. Is your new lines stainless? Try loosing and tightening lines a few times to seat the flair on the tube end. If stainless the metal is way harder than mild steel tube. You might already know this--good luck.

[Chris4x4Gill2]

Old or new fittings on the trans that the tubes attach to?

This might be an issue...Line fittings are screwed directly into the transmission housing. Should there be an adapter here? I thought it only required an adapter at the radiator end.

Lines are mild steel.

[Chris4x4Gill2]

I guess I need this kit?

https://www.inlinetube.com/products/INL10144

This project was mothballed for several years and I don't remember it having adapters on the original lines.

[cadillac_al]

Originally Posted by Chris4x4Gill2

I guess I need this kit?

https://www.inlinetube.com/products/INL10144

This project was mothballed for several years and I don't remember it having adapters on the original lines.

Yes you need those adapters. Cross your fingers that the threads aren't damaged in the trans.

[SunSoaked]

Ouch! If the end of a line is flared, there must be a corresponding inverted flare on the receiving fitting. If not, it's likely a pipe thread and should use Teflon tape or thread sealant. Be very careful not to get pieces of tape in the trans or you'll have other issues.

[Chris4x4Gill2]

Thanks guys. Fittings are on the way.

Use sealant on the threads or no?

[SunSoaked]

Yes, sealant or Teflon tape on the threads going into the transmission case, not the line to fitting side.

[95 S_Trucker]

Use thread sealant. I don't like Teflon tape on automotive applications.

I like this stuff:

https://www.permatex.com/products/th...hread-sealant/

[GASoline71]

Originally Posted by cadillac_al

Yes you need those adapters. Cross your fingers that the threads aren't damaged in the trans.

Was thinking the same thing.

Gary