When i press the gass it resist for about 2 sec then drops to the flor...
I'm thinking its the master cylinder ... but I really have no idea...
Tomarow I'm really going to look into it and try to fix it...

 

Check everything. Plain and simple.

 

+1

 

^lol

 

Your title says "What part of the brakes do I check?" Then you start with "when I press the 'gass'..." Anyways I'm gunna guess you're still talking about the brake pedal. You have air in your brake lines. First bleed all the brake lines including the master. Then when you have pressure check the master and all calipers for leaking while someone presses on the brake pedal.

 

You can have air in the system and still have brakes- just not very good ones.
Assuming there isn't a pool of fluid under one of the wheels, the symptoms he describes are from a bad master cylinder.

 

I mean when i press the brake.....

 

OK, that changes everything.
Oh wait...no, it doesn't, it's still the master cylinder.