What would cause a standard transmission to select two gears at the same time?

Selecting two gears at the same time in a standard transmission can be attributed to worn shift rail interlocks. The shift rail interlocks are designed to ensure that only one gear can be engaged at a time. They serve as a safety mechanism to prevent simultaneous engagement of multiple gears, which could otherwise lead to severe mechanical damage.

When the interlocks become worn, they may lose their ability to properly position the shift rails, allowing two gears to be engaged simultaneously. This phenomenon can create significant complications in transmission operation, including difficulty in shifting and potential damage to the transmission components from the conflict between gears.

While worn shift rail detents, shift lever fingers, and weak reverse plunger springs can contribute to other shifting issues, they do not directly cause the simultaneous selection of two gears in the same way that worn interlocks do. Hence, recognizing the role of the shift rail interlocks is crucial in diagnosing and addressing this specific issue in standard transmissions.