Master Cylinder Fitting Leak

[Robert Crandall]

I used a new reproduction master cylinder for a 1968 C10 to make a dual master cylinder conversion to a 1950 GMC. The new master cylinder looks just like the one shown in posts 11 and 12 of this thread:

http://67-72chevytrucks.com/vboard/s...archid=6375117

One fitting has a 1/2 inch thread, and the other has a 9/16 inch thread. I used new copper colored brake lines to each fitting. I cut the factory flare off one end of each line and put these new larger fittings on the ends with the factory flares still in place. I bought a Harbor Freight double flare kit, and, with great effort, succeeded in getting flares that were cocked only a little bit for the smaller fittings that tie into the other brake lines. These ugly flares hold with no leaks. The larger fittings with the factory flares both started out leaking, but I did manage to get the 1/2 inch fitting to stop leaking by tightening a lot more than I wanted to, but I did not strip it, so I'm ok there. I cannot yet get the 9/16 inch fitting to stop leaking.

I don't see why it would be so, but I will ask: Should there be a single flare instead of a double flare at these master cylinder fittings?

Is there something else that I am doing wrong with this?

Thanks.