1. The self-locking device is damaged: the self-locking device is the main component to prevent the transmission from shifting gears. If the self-locking device is damaged, the transmission will shift gears.
2. The synchronizer is seriously worn: the synchronizer is an important part to ensure the smooth shift of the transmission. If the synchronizer is seriously worn, it will lead to gear shifting or gear shifting difficulties.
3. Improper adjustment of gearbox control mechanism: Improper adjustment of gearbox control mechanism will lead to improper gear shifting or gear shifting.