I had a locked up brake caibler on the driver side so I replaced both sides and I also replaced both rubber lines as well. I bled the brakes the old fashion way and until I had a stiff pedal. Took it out and test drive it everythings good. Come morning to go to work goes straight to the floor. Pumped it up but still goes to the floor. So I bled them again but same story as before straight to the floor the next morning. I checked everything and I wasn't loosing any fluid. Air kept getting in the lines so I replaced the MC thinking it may have a internal leak. Did not fix it. So I plug the vuccum line and tape the hole on the booster. Started it up brake is stiff I can get my whole foot the pedal. I though if the booster was bad the brake would be extremely hard?

 

If you don't have any leaks its most likely your master cylinder, or do you have ABS? its really hard to say , I canyt understand exactly what you mean in the last sentence.