Thread: 45* vs 37* flares

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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?

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.

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