H E L P!!!
Brakes are fine right after they are bled. Then the pedal becomes spongy and with each successive brake application the pedal travels further to the floor until there is little hydraulic pressure and the car barely stops and then they have to be bled again. There are no fluid leaks and the lines are full of air. I am at a loss to explain it. I had to replace the rear wheel brake cylinders because the bleed valves were broken. This occurs within 5 to 10 pedal applications. The emergency brake is properly adjusted and fully functional. When you step on the brake pedal you can hear a hiss or vacuum sound from underneath the dashboard too. :-(
You can email me at snipped-for-privacy@cox.net or Post here. I'd be greatful for any help anyone can provide!