i have a 89 gta with all disk brakes. when i bought it i noticed the brakes were a little weak. i put new brake pads and it is still the same. most of the time when i stop i can floor the brake pedal and it wont stop but quickly roll to a stop. what can be wrong?

If the brake pedal goes to the floor, you need to bleed. Completely flushing out the brake fluid is a good idea if the stuff in the reservoir is brown/black/murky.