Dual Master Cylinder Brake Lines

[Stephen Dempsey]

I’ve installed a new dual master cylinder in my ‘64C. Unfortunately I can’t get to the point where I can bleed the brakes because the brake line connections leak where they meet the master cylinder. I hook everything up, add fluid to the reservoir, wait a couple of hours, and I have a leak. Is there a science to doing this correctly? I’ve never had problems with connections to the original single master cylinder. Thanks for any suggestions.

Steve

[Martin Benade]

Did you replace the lines? They need to be metric 10mm bubble flare if you get them at an auto parts store. 10 mm double flare will fit but the seal would be incorrect and not trustworthy although it could work. I think even a US thread brake line will screw in, but a loose fit on the threads and the wrong flare.
If you definitely have the correct lines just tighten them a bit more.

[Stephen Dempsey]

Thanks Martin - the lines came from one of our major vendors.

Steve

[Harlan Halsey]

Not science but maybe method. If they all leak it is one thing, if just one leaks then another. The line should fit in the socket stress free. That is, aligned straight with the hole and all the way to the bottom. The nut should be lubed, threads and line, with anti-seize, and screw in by hand all the way. Then make the seal by torquing the nut a bit. This assumes the parts are all correct, as Martin indicates. Pulling the line into place with the nut is asking for trouble.