What is the most common cause of loss of braking efficiency in an air brake system?

The most common cause of loss of braking efficiency in an air brake system is brake adjustment. Proper adjustment of the brakes is crucial because it ensures that the brake shoes make effective contact with the brake drums when the brakes are applied. If the brakes are not adjusted correctly, it can lead to a distance between the brake shoes and the drum that prevents the brakes from fully engaging, thereby diminishing their efficiency.

In contrast, while leaking hoses, worn brake drums, and damaged slack adjusters can also contribute to braking issues, they are less common. Leaking hoses can cause air pressure loss, but this is usually less frequent compared to issues arising from improper adjustment. Worn brake drums will eventually affect performance but typically develop over a longer period of time and can often be detected before they trigger significant braking issues. Likewise, damaged slack adjusters can cause brake application problems, but these components are generally checked regularly as part of vehicle maintenance routines.

Maintaining proper brake adjustment is fundamental for ensuring the effectiveness of the air brake system and should be a routine part of vehicle inspection and maintenance procedures.