I bought a 77 malibu master cylinder for my manual drum to disc conversion and I have a question about the bleeding process. I bench bled the master to death and after I bleed the front brakes when I go to refill the master again I refill the front brake resevor(sp) and I also have to refill the rear brake resevor too because it gets low. Why? is this a internal leak inside of the master? I have gone though 3 master cylinders in 3 months and all of them leak in one way shape or form.

The picture on this page (http://www.mpbrakes.com/mpfaqmasters.htm) may help you understand the "black magic" that occurs inside your MC.

Joe