Which of the following is a common defect in the suspension system?

A common defect in the suspension system is cracked or broken spring hangers. Spring hangers are crucial components that support the leaf springs and maintain proper alignment of the axle. When spring hangers are cracked or broken, it can lead to a misalignment of the suspension and affect the overall handling and stability of the vehicle. This may result in excessive wear on tires, alignment issues, and can even compromise the safety of the vehicle by leading to a potential failure of the suspension system during operation.

The other options, while important issues to address, are not related to the suspension system. Leaking fuel tanks pertain to the fuel system, worn brake pads affect the braking system, and faulty electrical systems relate to any electrical components within the vehicle. Hence, recognizing the significance of spring hangers in the suspension system helps in maintaining vehicle safety and performance.