When i brake the fluid reservoir tank seems to blow air from the inside?

I have a 2002 ford mustang and the brakes go really low when i use them and sometimes hit the bottom and it doesn t even brake. I noticed when i press the brakes it makes a air sound as if you re taking air out of a inflatible ball and under the hood the tank where you put the brake fluid into, bubbles blow up as if its getting air from inside the master cylinder. Im assuming getting a master cylinder would fix it but i want to make sure that it cant be any other problem

Read more: When i brake the fluid reservoir tank seems to blow air from the inside?