New Jersey Air Brakes Practice Test

What occurs when brake drums get very hot?

1. They cool down rapidly

2. They expand

3. They lose effectiveness

4. They shatter

The correct answer is: They expand

When brake drums get very hot, they expand due to the thermal energy generated from the friction during braking. This expansion can alter the clearances and fit between the brake components, which may affect the brake system's overall performance. Elevated temperatures can lead to a phenomenon known as brake fade, where the braking ability diminishes because the brake components can no longer maintain effective contact. This is partly due to the thermal expansion of the drums altering their shape and the distance between the brake shoes or pads, thus potentially resulting in reduced braking effectiveness over time. Understanding this expansion is crucial for maintaining safe braking performance, especially in heavy vehicles. The other potential outcomes, such as cooling down rapidly or shattering, are less likely in normal operating conditions and are not typical effects of heat on brake drums.