Topped off brake fluid a few dqys ago. Driving down the hwy I tried to brake but tne pedal went straight to the floor. No leaks at the brake lines, I changed the master cylinder and began the two man bleeding process. I hear air coming from somewhere, I wasn't ab,e to get any pressure while bleeding. The pedal almost wanted to stick when engaged instead of spring back li,e it should. Any ideas of what this issue is. Any tips on troubleshooting this problem. Thank you

 

sounds like the booster is bad... as for going to the floor, but no leaks, i would guess the something is physically broken in the booster. does the rod attached to the pedal slop around? i usually just change both if one fails after 100k, the other follows soon after in my experience.