pedal goes to the floor they tell me my master cylinder is bad

Hello,

If you press your brake pedal while standing still does it also go down to the floor? If not then I would suggest to have a look at your wheel bearings, ensure that the is no excessive play. A bad wheel bearing can cause a soft brake pedal as it can cause the brake disc to open up the brake calliper when going around bends. A link how to is below.

https://youtu.be/YvKWGjmPKoc

and

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

If you find nothing wrong with the wheel bearings then I would suggest to first bleed the braking system. Air in the hydraulic system can cause the brake pedal to be spongy. A how to instruction is below.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

If you still require to replace the brake master cylinder then please follow the general description below.

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

Please let us know how you get along.

Cheers, Boris