94 buick lesabre-brake pedal goes way down-left front/right rear wheels only braking

[niimcoinc]

94 buick lesabre brake problem. Pedal goes way down. Left front and right rear brakes hold (abs works on these). Right front and left rear brakes not holding at all. Fluid level is ok. No warning lights. Abs light goes out after about 3 seconds. Pads and shoes replaced. No apparent leaks. Parking brake works. What's the problem?

[maxwedge]

Welcome to AF. First, when and how did this star,t after work was done, or before any work was done, also check the link pertaining to bleeding with ABS. http://www.autozone.com/servlet/UiBr...3d8017faf2.jsp

[niimcoinc]

The problem occurred before any work was done. I don't know if it was a sudden or gradual loss of pedal. No work was done to any lines or cylinders. Thanks