Braking systems may not allow the vehicle to be without operative brakes capable of stopping the vehicle when loaded to manufacturers gross vehicle weight at any legal road speed. Brake lines shall be: Protected from excessive heat and vibration by means of a heat shield, if necessary; and Installed to prevent chafing, cutting, or stretching. Brake drums and rotors shall be permanently and plainly marked to clearly indicate, in legible cast or stamped legend, the maximum safe diameter of the drum or minimum safe thickness of the rotor beyond which it may not be used or machined, but shall be discarded.