89 Dakota 2WD 3.9 V6. Pedal goes to the floor with engine on or off. Won't pump up to a hard pedal. No leaks, MC full. With engine off, pumping pedal, I hearing a swooshing air sound. Brake light does come on and off when running. I can stop, but its not safe. No intake leaks at power booster hose or check valve. Bad valve?? I should add that sometimes the MC needs fluid and the rubber gasket on the cap has popped its nipple. But again, no visible leaks??

the light has come on either cuz there was a leak on one side of the system or the MC fluid got low enough on one half that the normal psi on one side pushed the electrical valve over to the low psi side till the light came on (that is what it is there for, to warn you). find/fix the leak then bleed the MC first then bleed the fronts then the rears till you get a high & tight pedal & if the light is still on (safety wise you are fine it just needs to be reset) & do that by cracking a bleeder on one side & have a helper jab the pedal to shift the valve back to "centered" in the prop valve & it will be out. be carefull not to lift pedal till he closes the bleeder to avoid drawing air back up into the system & I ain't sure which "side" sprung the leak but when fixed you open a bleeder on the opposite side. which "half" was the leak on (if it was a leak). PS out a block of wood under the pedal so that it does not go lower than "normal" & this helps your helper control/stop the movement way better.

What's up RR? Long time no talk. Anyway, there is no leak to be found.

Yes it has been awhile. Yeah there's still some air in there & I'd bleed the MC then the fronts then the rears

Since there are no external leaks,the master cylinder could be bad and leaking internally between the bore chambers.No fluid loss into the booster/vacuum line either correct?

Correct, everything is dry

Sounds to me like a bad master

In fact it was! Had one tucked away for a rainy day. All better now. Thanks guys!!