A manual shift transmission slips out of fifth gear. What is the most likely cause?

• A. A broken detent spring
• B. Too much shaft and gear spline wear
• C. Worn countershaft bearings
• D. A chipped countershaft drive gear

Answer: (A)

The gear is kept in place by a detent mechanism that uses a spring to bias a detent ball or roller into a groove, locking the gear in the selected position. If the detent spring breaks, the detent no longer holds the gear, so under load the gear can pop out of engagement and slip out of fifth. This is the most likely cause because it directly affects the locking action that keeps a gear in place, whereas wear of splines or bearings or a chipped countershaft gear would produce different symptoms like excessive play, noise, or grinding rather than a simple slip out of gear.