What is the likely cause of a noisy transmission in reduction ranges and reverse, but normal in direct drive?

A noisy transmission in reduction ranges and reverse, while operating normally in direct drive, suggests that the issue is likely related to the components that engage during those specific ranges. Worn planetary gear sets or thrust bearings are crucial in the operation of a transmission, particularly in lower gears and reverse.

When the transmission is in reduction ranges or reverse, it relies more heavily on the planetary gear sets to manage the power transfer from the engine to the wheels at the appropriate ratios. If these components are worn, they can cause excessive play or misalignment, resulting in noise due to the movement of parts that should be tightly fitting. Worn thrust bearings can also lead to similar issues, as they help maintain proper spacing and alignment between the gears.

In direct drive, the transmission is generally using a simpler, more straightforward power route without engaging the complex gearing and thrust bearing arrangements that are more present in reduction gears and reverse. Therefore, the absence of noise in direct drive further supports the notion that the root cause lies within the more heavily loaded components during reduction and reverse operation.