A brake system for a wheelchair comprises a lever assembly adapted to be movably connected to a wheelchair frame, the lever assembly having a handle portion for hand manipulation. A brake unit is adapted to be pivotally connected to relative to the wheelchair frame, the brake unit having a brake end adapted to contact the wheel. An actuator portion and a follower portion are in the brake system, the follower portion cooperating with the actuator portion for the brake unit to be selectively displaceable between at least two configurations, including a floating configuration in which the brake end contacts the wheel so as to automatically pivot into blocking contact with the wheel when the wheel rotates rearwardly, while allowing a forward rotation of the wheel, and a locking configuration in which the brake end is manually locked into blocking contact with the wheel.