Semi trailers made before 1975 that are equipped with air brakes often lack what feature?

Semi trailers made before 1975 that are equipped with air brakes often lack spring brakes. Spring brakes are a safety feature designed to apply the brakes automatically if air pressure is lost in the braking system. This technology became more standardized after the introduction of federal regulations that required these safety measures for newer vehicles.

Older models, particularly those manufactured before 1975, may not have this feature due to the technology and standards that were available at the time. Instead, they typically relied on service brakes that required continuous air pressure to remain engaged. The absence of spring brakes in these older trailers means that if there is a failure in the air system, the trailer may not stop as effectively, leading to safety concerns.

In contrast, air compressors, load sensing brakes, and emergency braking systems were more commonly integrated into braking systems as manufacturers evolved their designs and regulations became stricter, especially after the mid-1970s. Understanding this context highlights the importance of vehicle maintenance and retrofitting older models to meet modern safety standards.