Brakes

Sounds like the cylinder.

It could be many things. Was the pedal firm when it went to the floor or soft? When you pumped them did the pedal pressure change or did they simply start working?

A soft pedal often means air in the system that a normal bleeding process can't always get (a flush or full-bleed is in order).

But if there is air in the system then pumping the brakes wont make much difference, so I am going to guess you have a leak somewhere. Check all four wheels for signs of leakage. If you find none check the master cylider or trace the lines. If you still don't see any signs of leaking then maybe it is your power booster.

Good luck, drive VERY carefully until you fix it and let us know what it is/was when you do.

Here's the logic/mechanics...

If you have air in the lines they will be mushy and pumping will not alleviate that.

Since pumping them made them work then what most likely happened is that the pressure in the lines was able to overcome the bleeding effect of the leak (you could put pressure into the lines faster than it leaked out).

You could have an obstruction in the line too, same effect...pumping adds a lot of pressure that overcomes the unwillingness of the fliud to move. You could have rusted linies, DOT3 attracts moisture like crazy and the lines can rust from the inside.