What is the most common cause of bearing damage as shown in Figure 3-21?

Fatigue is the most common cause of bearing damage in the context of manual transmissions. This type of failure occurs when bearings are subjected to repeated loading and unloading cycles over time, leading to the gradual breakdown of the material structure. As stress is applied to the bearing surfaces, microscopic cracks can develop, which eventually lead to larger fractures and surface pitting.

In components such as those found in manual transmissions, bearings endure significant mechanical stresses due to forces from gear engagement, which can contribute to fatigue. Factors such as misalignment, improper lubrication, and subpar materials can accelerate this fatigue process, causing premature failure. Understanding this can help technicians identify and mitigate the risks associated with bearing wear, ensuring a longer lifespan for transmission components.

The other potential causes, while relevant in different contexts, do not encompass the broad scope of issues that fatigue can induce over time. Overheating, for instance, can lead to clear and immediate damage but does not represent the cumulative effects seen with fatigue. Similarly, wear is a result of various operational conditions, and improper handling typically causes immediate and apparent damage, unlike the gradual deterioration associated with fatigue.