What is the reason for not being able to shift gears when the clutch is pressed down?

[SanMaddox]

Common causes of difficulty in shifting gears or inability to shift when the clutch is pressed down include the presence of debris in the clutch, improper adjustment of the booster push rod's travel, air in the clutch hydraulic system, or excessive free travel of the clutch pedal. Below are the correct operations for shifting with the clutch: 1. Avoid prolonged semi-engagement. Some drivers have poor driving habits, unconsciously keeping their foot on the clutch pedal while driving, which keeps the clutch in a semi-engaged state. The left foot should be moved away when the clutch is not in use, as prolonged semi-engagement accelerates clutch wear. 2. Fully depress the clutch before shifting. If the clutch pedal is not fully depressed, shifting gears can cause a "gear grinding" phenomenon, which is very harmful to the transmission if done frequently. 3. Only depress the clutch pedal when braking at speeds below 20km/h. Depressing the clutch pedal at higher speeds does not assist in braking effectiveness. Of course, during emergency braking, both the brake and clutch should be pressed simultaneously.