Which of the following indicates a problem with brake discs?

A crack extending to the edge of the brake disc is a significant indicator of a serious problem. Such cracks can compromise the structural integrity of the brake disc, potentially leading to brake failure during operation. Brake discs are critical components of the braking system, and maintaining their integrity is essential for safe vehicle operation. Cracks indicate that the disc may be weakened and could fail under the stress of braking, which can result in dangerous driving conditions.

Surface rust is common, especially if the vehicle has been sitting for a while, but it typically doesn't affect the performance of the brakes if it is light and superficial. A shiny finish on the discs can indicate normal operation and wear, as the surface can become polished from use; it doesn't necessarily imply a problem. Normal wear and tear is expected in brake components, and as long as the discs are within manufacturer specifications, they can continue to function properly. In contrast, a crack extending to the edge represents an immediate risk and warrants replacement of the disc to ensure safety.