97 lincoln continental brake problem

Hi,I have problem with my brakes.When I apply brake pedal while driving,noise is heard and brake pedal goes down further than initial contact point.No warning lights come on.I have replaced master cylinder and power booster.I have checked the front and rear brake pads.They are like new,rotors like new also.I understand that these brakes have to be bleed using a special gismo on the abs computer.I do have traction control on this car. I think its possible that the proportioning valve could be bad. Anybody experience this problem?HK