brake master cylinder replacement

At this point the issue is most likely the master cylinder leaking internally.
Also it could a brake line issue that is swelling when you press the pedal. However, this will normally cause a soft pedal and not going to the floor. So I would think the master cylinder is leaking internally. Here are the master cylinder installation instruction you have requested. Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://youtu.be/WDxvEQrMkBg

and

https://youtu.be/w7gUsj2us0U

and

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

If you take the lines off and cap the outlets of the master cylinder then press the pedal if it still goes to the floor then you know if it is leaking internally because you have eliminated the rest of the braking system.

Let me know if you have questions. Thanks