45* vs 37* flares

[firebird77clone]

I just borrowed a 45* double flare tool for my transmission lines. But the flare tool I was looking at to purchase is a 37* flare tool.

Which is the right one, and is that 8* difference critical?

[Hotrod46]

Most trans cooler lines on older American cars are inverted flare fittings. The 45* is correct for that. You will need to double flare the lines for a proper connection. The flare tool will have a set of double flare inserts that create an upset in the end of the tubing that is then rolled back into itself to make the "double flare".

The 37* is for AN type fittings. The AN is much easier to do IMO and is made to be disconnected many times without damage. I use them for just about everything now, but still need the old double flares, too.

Yes, the difference is critical.

Post a pic of your cooler fittings so that we can know for sure what you have.

[34_40]

General rule of thumb was steel brake lines need 45' double lap flares. And 37' is for Stainless Steel brake lines.