BUICK LUCERNE BRAKE SYMPTOM

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...

At Low Speeds When I Brake The Car Shakes. The Steering Wheel Does Not. It Doesn't Seem To Be The Tires. What Could This Be? I Just Had...