[thefro526]

Are you talking about a car style brake or a brake that contacts the floor?

If it's a car style brake where it uses some kind of mechanical force to slow down the speed of the wheel to slow the robot down it should be legal, but you should be able to accomplish the same effect by putting the jumper on the speed controller into the brake position.

If you're talking about a brake that would contact the playing surface then no. It's not legal because nothing is allowed to touch the playing field except the wheels of a robot.