Answer :
Final answer:
Hard spots in brake drums are primarily caused by excessive heat and pressure generated during braking. While other factors can contribute to brake drum issues, they do not directly lead to the formation of hard spots. Overall, managing heat in the brake system is crucial for performance and safety.
Explanation:
Causes of Hard Spots in Brake Drums
Hard spots in a brake drum can be attributed to several factors, but the most significant cause among the options provided is excessive heat and pressure. When the brake system operates, it generates a substantial amount of friction, which can lead to high temperatures. This excessive heat can alter the material properties of the brake drum, creating hard spots that affect performance and safety.
- Improper mounting of the drum on the lathe (Option A) can lead to uneven wear but is not a direct cause of hard spots.
- Machining a drum at too high a speed (Option B) may generate heat, but it is not the primary cause of hard spots.
- Using a rubber belt to dampen vibrations during machining (Option C) is a good practice, but failing to do so doesn't directly lead to hard spots.
Therefore, excessive heat and pressure from braking is the most appropriate answer, as it is the direct cause of the changes in material characteristics that result in hard spots.
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