I have a 61 sedan, drums on all 4 wheels. This thing is ready to get back on the road but the only thing keeping her in the garage are some brake issues. I decided to stick with drum brakes, but I did do the dual bowl master cylinder conversion. Did all new lines, new wheel cylinders, new brake shoes, and new drums.....but good braking eludes me. The thing I seem to be fighting is excessive brake pedal travel and a soft brake pedal. The brakes work, but not until the pedal is on the floor and sometimes you do have to pump the pedal a few times for the brakes to catch. But that good braking power seems to go away after about 10 seconds and then you have to pump them again to stop. I have tried the following: excessive brake bleeding(both gravity and traditional types), adjusting the brakes on all 4 wheels for drag, and playing with the bolt that connects the master cylinder pushrod to the brake pedal. Any ideas? I'm at wits end trying to figure out what is going on. Only thing that I can think of is if I got the wrong size bore on the dual master cylinder I used for the conversion. I believe I got one with a 1" bore....it would be one that would be compatible with a 1967 mustang with drums on all wheels. Also I was reading about residual valves too....would it help to add some of those to my brake setup?

I'm open to any suggestions! Thanks!