Disk brake causes vibration
 

When I brake hard my whole mustang starts vibrating. I think my disk brakes aren't straight anymore. Is it possible to straighten them on a turn bentch (I don't know the translation of this machine so I made one up). Or does this damage more then it fixses. Can these disks also produce a vibration while driving because a vibration I feel while driving has the same frequency only much softer than while braking

Trying to straighten them is a really bad thing. What u need to do is to take them to a shop, and get them turned, along with new brake pads.

What hapend was either u ride the brakes too much, or u hit them too hard, causeing them to heat up and warp. The only way to fix this is to buy new brake pads and get the rotors turned. Or buy new ones.

Out of round tires?
 

Since it does do it anyway to a lesser extent even when not applying the brakes, it might be out of round tires causing that vibration. If it is the front tires out of round, it would increase the vibration on braking. In short, it might not be the brakes at all.

Put a dial indicator on the rotors and rotate them to check the run out (variation). If more than a few thousanths and if any scoring of the surfaces on the rotors, I would get them turned at a good machine shop along with installation of new pads. I still think it may be the tires though, since the vibration is not entirely limited to braking.

Rev

Agreed. My 97 Mustang was doing the same thing so last month, I took the opportunity to finally get and install some cross drilled rotors and new pads. Runs great now!