Which principle does NOT apply to leaf spring suspension repair procedures?

The principle that states "Never retorque the nuts that fasten U-bolts" is not applicable to leaf spring suspension repair procedures because it is common and indeed necessary to retorque U-bolts after installation or after a period of use. This is to ensure that the nuts are properly secured and that the suspension system maintains its integrity and performance. U-bolts can settle over time, and retorquing them helps prevent any loosening that may lead to suspension issues or unsafe driving conditions.

In contrast, the other options reflect established practices in leaf spring repairs. When a truck has run with a broken spring leaf, it is vital to replace the entire set to maintain balanced handling and load-carrying capacity. Simply replacing a single leaf can lead to uneven performance and compromise the safety of the vehicle. Similarly, never reusing U-bolts is essential because they can undergo deformation during initial installation, and reusing them may lead to failure. Therefore, maintaining reliable and safe repairs involves adherence to these well-established principles.