I had this exact same problem on my 49 Sub. I adjusted the rear shoes up tighter to no avail. I bled and re bled. I was ready to live with the problem because after one pump I had good brakes. I then took it to a local garage for an oil change that still has a couple of gearhead mechanics. While up on the lift the one gearhead asks me "do you know you have the lines connected to the master cylinder wrong?" No I replied, does it make a difference? Yes, he says, front brake lines go to the front port of the master cylinder and rear brake lines go to the rear port of the master cylinder. I had him change them around and problem solved.
Weeds
