To add a little to the above descriptions... the balance bar has an adjustable pivot between the two master cylinders. Basically, the pedal arm has a horizontal tube (visible in some of the pictures above) where the push rod would normally connect. Inside the tube is a ball on a threaded bar that connects to the master cylinder push rods. When you turn the threaded rod it moves the ball toward one master cylinder and away from the other so that one master receives more mechanical pressure than the other and thereby changes the brake bias. A lot of stock cars have a knob or small crank on the dash so brake bias can be adjusted while driving, but that part is usually not necessary on the street.