Mitsubishi Repair: 95 eclipse gs 2.0, master brake cylinder, brakes rotors

Question
i just recently changed my brakes rotors and calipers on the front of my car and since then my brakes do not seem to work when going over 15 or 20 mph the pedal is just lose and its like the brakes arent even working if im moving slowly they grab very well and feel like new but any little speed and its like they arent there

Answer
Francisco,
Since you replaced the calipers, you would have needed to bleed the brakes; front and rear.  Else, you'll get pockets of air trapped in the brake lines which can cause the problem you're experiencing.  You didn't mention if you replaced your brake pads.  If the pads have significant wear on them, they should be replaced as well.

If you bleed your brakes completely and you're still having problems, you should have your master brake cylinder inspected and replaced if necessary.
Good luck!