What is the reason why the car cannot shift gears when the engine is off but can shift when the engine is running?

[LaMaya]

The reason is that the clutch cannot completely disengage, or the positioning part of the shift lever's ball head has lost its function. Here is some relevant information: 1. Introduction: The clutch is part of the car's transmission system, and this component is very important for the vehicle. The clutch is responsible for connecting or disconnecting the engine and the transmission. It is installed between the engine and the transmission. The clutch pressure plate is fixed to the engine flywheel, and between the pressure plate and the flywheel is the clutch disc. 2. Precautions: When stopping the car, pressing the clutch is equivalent to cutting off the power. At this time, the brake acts on the tires and has no effect on the engine operation, so it will not cause the engine to stall.

[NevaehFitz]

I've heard many car enthusiasts complain about difficulty shifting gears while driving, but it becomes smooth after turning off the engine. This is often due to incomplete clutch system disengagement. Severe clutch disc wear or pressure plate deformation can prevent complete power disconnection when you press the pedal, and forced shifting can damage the gears. Hydraulic system failures are also common, such as master cylinder seal failure or fluid leaks in the oil lines, making the pedal feel soft and weak. Regarding the transmission, synchronizer wear can cause rough shifting with gear grinding noises. The reason shifting works after turning off the engine is that the gears stop rotating without synchronization pressure when the engine is off. If not repaired promptly, the entire transmission assembly may require major overhaul, leading to skyrocketing repair costs. It's advisable to avoid long-distance driving and have a reliable repair shop thoroughly check the hydraulic fluid level and clutch clearance.

[DelIsabela]

If the gear doesn't engage properly and the car stalls while driving, I suggest you do some preliminary checks yourself. First, check if the fluid in the clutch reservoir is clear enough, and top up with hydraulic oil of the appropriate grade if it's low. Second, test the pedal pressure; if it feels too light or too heavy when pressed, it might indicate a pump or valve failure. Third, start the engine without moving, press the clutch, and shift into forward or reverse gear to listen for any grinding noises. If you notice any abnormalities, it's best to turn off the engine immediately and avoid forcing the gear. Safety first—make sure to operate on level ground to prevent the car from rolling. If these steps don't help or you find them troublesome, call a tow truck to take the car to a repair shop where a technician can use professional tools to check for drive shaft wear. Don't risk driving on the highway to save time—it's too dangerous.

[McLane]

This issue is quite dangerous, don't underestimate it. Difficulty in shifting gears leading to stalling indicates clutch or transmission mechanism failure. If you can't shift while driving, immediately pull over, engage the parking brake, turn off the engine, and check for any warning lights on the dashboard. Forcing the vehicle to move may lock the gears and destroy the transmission, potentially doubling repair costs. For safety, towing it to a repair shop is the correct solution. Develop good habits by shifting to neutral when parked as a precaution.