What is the likely cause of a scraping sound coming from the rear brake that stops when the brakes are applied?

A scraping sound coming from the rear brakes that ceases when the brakes are applied typically indicates that a component is not fully secured or is misaligned. In this case, the correct answer points to a broken shoe hold-down spring or pin. These components are crucial for keeping brake shoes properly positioned within the drum assembly. If the hold-down spring or pin is compromised, the brake shoes can move out of position, resulting in contact with the brake drum and generating a scraping noise. When the brakes are applied, the shoes press firmly against the drum, temporarily resolving the misalignment and thus silencing the scraping sound.

On the other hand, a broken brake line would lead to hydraulic issues such as loss of braking power, rather than a scraping noise. A malfunctioning brake booster primarily affects the power assist to the brakes and typically would not cause a scraping sound in the manner described. Worn brake pads can produce a grinding noise as they reach the end of their lifespan, but not necessarily a scraping sound that stops upon application of the brakes. Therefore, recognizing the specific characteristics of the noises associated with brake components is essential for accurate diagnosis.