When testing your tractor-trailer hook-ups, when should you stop pulling against the locked trailer brakes?

Stopping pulling against the locked trailer brakes when you feel the engine start to drag down is important because it indicates that the tractor is applying a significant amount of power to move the trailer, yet the brakes are still holding it in place. If you continue to pull against the locked brakes after feeling this drag, it can lead to excessive strain on the engine and drivetrain components, which may result in mechanical failure or unnecessary damage.

This shows that the vehicle is functioning as intended, where the driver must ensure that the trailer is correctly connected and that the brakes are functioning properly before moving on. This step reflects a critical aspect of safety checks in tractor-trailer operations prior to travel, ensuring that all systems are go and the equipment is reliable for safe driving. By confirming that the trailer is free to move, you set the stage for a safe departure and avoid potential hazards that can arise from overlooked mechanical issues.