2002 Ford Explorer • 160,000 miles

Brake pedal will sometime go down almost to floor with nothing happening. Have checked fluid, have inspected for leaks in lines and calipers, can not hear any vacuum leaks. This only happens once in awhile. The rest of the time the brakes work fine. Also there are no warning lights coming on.? Could this be something with the anti lock brakes?
October 15, 2013.

It sounds like the MC is going bad.