What are the reasons for not being able to shift gears when the clutch is fully depressed in a manual transmission?

[MollyFitz]

Here are the reasons why a manual transmission car cannot shift gears when the clutch is fully depressed: 1. Clutch cable failure: Some manual transmission cars still use cables to control the clutch. The outer sheath of the cable can easily crack, leading to difficulty in shifting gears due to no clutch engagement. The solution is to directly replace the cable. 2. Excessive gear self-locking force on the clutch side: This can cause difficulty in engaging and disengaging gears. It is recommended to go to a repair shop to adjust the clutch cable and gear stop lock. 3. Clutch master cylinder failure: The clutch hydraulic master cylinder may experience pressure loss or oil leakage during use, resulting in the inability to shift gears when depressing the clutch. In this case, the clutch master cylinder needs to be replaced at a service station, followed by an air bleeding operation. 4. Transmission failure: Issues such as insufficient transmission fluid, stuck transmission shift mechanism, or failure of a specific gear or shift fork can all lead to difficulty in shifting gears or the inability to engage a gear. For transmission-related problems, a detailed inspection at a professional repair shop is necessary.

[VonKai]

I've encountered this issue several times. With prolonged manual transmission driving, it's common for clutch wear to cause incomplete disengagement. When fully depressed, the clutch disc doesn't completely separate the engine from the transmission, naturally making it impossible to shift gears. Another possibility is a hydraulic system leak, where insufficient oil pressure makes the clutch pedal feel lighter; my car once had this issue, and upon inspection, a minor leak was found in the slave cylinder. There's also the aging of synchronizers, making gears hard to engage. This is more likely to happen in cold weather when oil thickens. I recommend starting with a simple check of the clutch fluid reservoir to see if the level is low. If everything seems fine, avoid forcing the gears and take your car to a professional mechanic for inspection as soon as possible. Regular maintenance can prevent such issues, like changing the oil every six months. Older cars require extra attention to these details after years of driving.