My brakes are going down to the floor...help?

I have a 1992 Oldsmobile 98 and an anti-lock brake system. My brakes are going down to the floor and the pads are fine. I have brake fluid and my lines have been bled....I know there is no leak so could it be that my brake lines have air in them and if not what else could it be? All answers are appreciated....Thanks!!!|||replace the master cylinder...cheaper than rebuilding it...then bleed all brakes.....pump up the pedal 10 times...and start at the wheel farthest from the master cylinder...work your way to the closest wheel..and you will be fine ...good luck|||it could be air,but i think its probably the master cylinder went to lunch.you dont get air unless you break a line or hose,or a leaking wheel cylinder,so iam leaning towards the master cylinder.|||master cyclinder brake pump the valve is broken/worn out .. theres a repair kit for that..|||Have the whole brake system re-bled first off. If the brakes are still sinking, have the brake slave cylinder checked. It could(although it's reaching here for a solution) also be the vacuum assist on the brake cylinders(by the way, it's either right behind or right next to the brake master cylinder assembly). If it's not that,. last but not least, don't adjust it just replace the brake cable. You will have to have it properly pre-streched and adjusted BEFORE driving though. When the brakes on a car have been completely and properly bled, you should barely be able to put pressure on the brake pedal BEFORE the car immediately starts to stop! Check all the brakes out for leaks and the lines too.|||Sounds like your master cylinder.