Final answer:
The main cause of transmission bearing failures is a lack of lubrication. Improper shifting can also contribute to these failures. Operation on rough highways and dirt are not the primary causes of bearing failures.
Step-by-step explanation:
The main cause of transmission bearing failures, as stated by transmission OEMs, is a lack of lubrication. When the bearings do not have enough lubricant, they experience increased friction and heat, which can lead to premature wear and failure. Proper lubrication is crucial to ensure smooth operation and prevent damage to the bearings.
Improper shifting can also contribute to transmission bearing failures. When gears are not shifted correctly, it can result in excessive load or shock on the bearings, causing them to wear out more quickly.
While operation on rough highways and exposure to dirt can affect the overall condition of a transmission, they are not typically cited by transmission OEMs as the primary factors leading to bearing failures.