Final answer:
Bad brake drums or shoes can be identified through symptoms like unusual noises, the vehicle pulling to one side during braking, loss of braking power, a spongy brake pedal, and visible smoking brakes.
Step-by-step explanation:
The signs of bad brake drums or shoes in a vehicle can include a variety of symptoms. Some common indications are strange noises such as squealing, scraping, or grinding when the brakes are applied. These noises are usually a result of the brake shoes wearing down, which causes them to come into direct contact with the brake drums, leading to increased friction and heat. Another sign can be when the vehicle pulls to one side during braking, which could be caused by uneven wear or damage to the brake shoes or drums. Additionally, a loss of braking power or a spongy feel when the brake pedal is pressed can also be indicators of worn brake components. A visible sign of bad brakes can be the presence of smoking brakes, as shown in FIGURE 14.5, where the brakes of the truck are emitting smoke due to the conversion of kinetic energy to heat. This is an example of the mechanical equivalent of heat, where mechanical work is transformed into thermal energy, much like when a book sliding across a floor heats up due to friction.