Master cylinder was replaced brake pedal goes to the floor

When you replaced the master cylinder, did you bench bleed the master cylinder prior to installing it?

If not, then I suspect you are not getting the air out of the system.

Here are a couple guides that will help with this:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

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

However, the place to start if you did bench bleed it is to cap the master cylinder ports and see if you have a hard pedal. If you do, then you have a leak or air in the lines somewhere else in the system.

This means you need to add one line back in at a time until you find where the pedal gets soft again.

Please run through this and let us know what questions you have. Thanks