In the event of sliding mesh gearbox, the output shaft gears continually rotate While using the output shaft although in other gearbox, the output shaft gears are mounted with bearings hence these gears rotates independently. Sensors in automatic transmissions use interior oil pressure to change gears at the appropriate time. https://gearbox-auto31963.ttblogs.com/13446783/not-known-details-about-gearbox-auto