Which condition warrants a vehicle's rejection due to the brake drum and braking components?

A vehicle should be rejected due to substantial cracks that extend to the edge of the drum or disc because this condition directly affects the structural integrity and functional performance of the braking system. Cracks that reach the edge indicate significant stress and potential failure points where the brake components could fracture during operation. This situation poses a serious safety risk as it can lead to brake failure while the vehicle is in motion, greatly increasing the likelihood of an accident.

While excessive rust on the drum's surface can affect braking performance, it may not pose an immediate risk of catastrophic failure as cracks do. Visual dirt on the exterior of the wheel is largely cosmetic and does not impact the functionality of the brakes. Improperly mounted wheels can create other safety issues, but they do not directly relate to the braking components themselves like substantial cracks do. Hence, identifying severe cracks in the brake components is critical for ensuring the overall safety and reliability of the vehicle.