When i drive for long distances or for a long time period i have to step on my brakes all the way down for my car to stop. I step on the brakes and it just slowly goes all the way down. any idea whats wrong? this doesn't happen if i drive for short time periods.

 

Probably the master cylinder.

 

maybe you can try to bleed the brakes to see if that helps, i don't think its a bad master cylinder.

 

Have your brakes recently been worked on? Are you losing fluid? If the answer is no to both questions, then the master cylinder most likely is bad.

 

get it checked out and fixed asap. It sounds like the master cylinder is bad. It can go out completely randomly and you wont have brakes...

 

It could very well be air in your lines. I'd either get them bled or wuld do it, myself, but only if I limited the brake pedal travel. You could easily damage the master cylinder piston seal by over-extending the piston. (which you've probably already done). Now that I think of it, you may have to change the MC and flush the fluid. While you're at it, check the rotors for excessive runout which can lead to air getting pulled into the brake fluid.