Hi and thanks for using 2CarPros.
If the brake pedal goes to the floor, then the master cylinder is bad. I am basing that on the fact there are no leaks and the master cylinder still has fluid. If that isn't happening, let me know. However, if the brakes aren't working at all, there really isn't another cause. Individual components can go bad, but that won't cause all brakes to fail.
Here are the directions for replacing a master cylinder as well as an explanation of what can cause the brake pedal to go to the floor:
Let me know if this helps or if you have other questions.
Saturday, January 26th, 2019 AT 9:45 PM