1999 Chevy S-10 brake light

Brake light on, pedal sinks to floor, has little braking.
brake fluid level good ! No leaks at lines or all four wheels.
no fluid on inside brake pedal rod under dash.
breifly unplugged hose on booster and heard suction noise and plugged back in. I had replaced a front hub approx 500 miles earlier and everything appeared to be working just fine after that repair and than 500 miles later light comes and soft brake pedal and decreased braking.