I have a 05 gt and my brakes keep getting air in them. I've bled them. Changed the master Cylinder twice did pretty much everything, it works for a little while but they end up going to the floor before it will stop. Idk what else to do.

 

New lines? I have the same issue, and I suspect a line may be bulging.

 

If you're getting air in the lines, then you probably have a leak, and it's likely past the master.

The brake lines are hard piping until it gets to the calipers at each corner, then the hoses from the hard lines to the calipers. All that needs to be inspected for tightness and leaking.

I would do this: Jack all four corners up and put it on jackstands so as to have the car in the air, and be able to pull the wheels off.

Once on the jackstands, pull the wheels off, and thoroughly inspect the calipers and hoses, and where possible the hard lines to ensure there's no leaks. It should be obvious.

Also, get a buddy to get in the car and hit the brakes as you look. You might see a weep or an actual leak somewhere that way. Or as mentioned above, a bulging hose. Be sure to protect your face, 'cause brake fluid isn't eye friendly.

After that, take the calipers off one by one and inspect the piston seals for leaks.

Hope that helps ya!