Sounds like there may be air in the system or there may be an external leak. Have the system checked at a shop for any leaks and make sure the bearings in the front and rear have no play as they may also cause a low brake pedal.
October, 13, 2011 AT 2:03 PM
Who is doing the parts replacing/recommending? No way you would have to replace pads/rotors/shoes since they were working fine when parked! Get help from competent people!