replacing rear brake cylinders...

I'm wondering what is the best way to free the brake line from the wheel cylinder. I know that you have to use a hex wrench. I have to go buy one as I don't have any and what the size is.. (guessing 3/8 or 10mm)

Buy a set of tubing wrenches. They encompass more of the fitting making it less likely to round the corners off. They are available at any Sears or parts store.

I usually take a little wire brush and clean up around the fitting and spray a little Releasall, WD-40, penetrating oil....whatever on it and let it sit for a while. Then I use a line/tubing wrench and give it a little tap with a hammer rather than applying the turning force with my hand to free it up.

I've removed very rusty lines from wheel cylinders where the line was basically fused to the fitting from rust. Then the line turns with the fitting and you end up replacing that section of line. It's a pretty small section of line anyway, and doesn't take too much time and cost too much to replace it while you're there.

As said spray with rust buster-and wire brush around the fitting(on the line behind the fitting) its 3/8 i think...

Tighten it before ya loosen it and watch for the line to try and spin as the last poster said-usually if you keep going back and forth (tighten/loosen) it will break free from the line-a small plumbers torch can help too...

A trick I learned from watching my cousin in his shop is to hold the line steady and actually turn the cylinder, not the nut on the line. Sometimes it works, depending on rust factor, etc. Keeps the line from accidentally breaking or bending.