Buick Lucerne Brake Pedal Goes to the Floor

It Had A Leak In A Brake Line. Replaced Both Lines To Rear. Bled System. I Had To Replace The Master Cylinder. Bled Lines Using Vacuum Pump...

The Brakes Were Fine Making No Noise. Next Thing Is All Of A Sudden They Went To The Floor. Checked The Doesn't Seem To Be Leaking....

I Replaced The Brake Pads On All Four Brakes.. Had A Tough Time Getting The Pistons Pushed Back In, So I Opened The Bleeders. One Bleeder...