Lost all brakes today. No pressure, No pedal, No fluid leaking, . Started up my truck put foot on brake pedal to put in gear and as soon as it went into drive the pedal went to the floor. Resivor is full . Any suggestions? Thanks

 

Master cylinder is bad if pumping doesn't get pressure back and no leaks at wheels or lines

 

Thanks Ron had a feeling that was it. Double checking. If pushing brake pedal when truck is not running it's a little tighter. As soon as I start it boom right to the floor.

 

Another question? Could it also be the vacuum booster?

 

No, because it "goes right to the floor" with engine on, which means its working

All the booster does is "assist" the driver with pedal pressure.

Open a bleeder and have someone press down on pedal, engine off, should get a good long squirt of fluid, if not the master is not "sealed" inside, probably pushing fluid up into the reservoir instead of down the brake lines.
Fluid will come out of an open bleeder, but should be with some force behind it not just gravity

 

Thanks . I'll try that