I recently noticed a few days ago that my breaks werent as sharp as they usually are. sometime they felt good and other time i had to put my foot to the floor before i could stop. today i lost them completely . if i pump the break i get them for a few seconds and then they are gone again. i checked the fluid and it was full. does this sound like the master cylinder is gone?

 

In order to properly test the master cylinder on the vehicle you'll need two metal plugs that fit the hydraulic ports on the master cylinder. You'd typically remove both hydraulic lines and install these plugs. Then push the brake pedal down hard and hold. If the pedal sinks or goes to the floor, the master cylinder is bad.

If your sure there are no signs of fluid leaking at any of the wheels and none of the flex lines are bubbling under pressure then based on your description its more than likely the master cylinder.