What happens if the trailer supply line has a gradual leak?

Answer: C — It prevents automatic spring brake application

If the trailer supply line has a gradual leak, the proper consequence is that it prevents automatic spring brake application. In a typical air brake system, the spring brakes are designed to engage when air pressure drops below a certain level. This mechanism ensures that if there is a failure or significant drop in air pressure, the spring brakes will activate, bringing the vehicle to a stop for safety. However, with a gradual leak in the trailer supply line, there may not be an immediate and significant enough drop in pressure that triggers the automatic application of the spring brakes. Instead, the system may lose some air pressure over time, but it might still retain enough pressure to keep the brakes disengaged. This situation means that the spring brakes do not automatically engage as they should, potentially leading to dangerous conditions if the air pressure continues to decrease. Therefore, understanding the implications of a gradual leak in the trailer supply line is crucial for maintaining vehicle safety and ensuring proper braking functionality.