What is the reason for the abnormal noise in manual transmission idle speed disappearing when the clutch is pressed?
3 Answers
The reason for the abnormal noise in manual transmission idle speed disappearing when the clutch is pressed is: problems with the transmission bearing, looseness or detachment of the release bearing causing vibration and abnormal noise. When the clutch pedal is pressed, the bearing is pressed against the clutch pressure plate, causing the bearing to rotate, at which point the abnormal noise disappears. The functions of the clutch are: 1. Gradually increase the driving force of the car, allowing the car to start smoothly; 2. Temporarily separate the engine and transmission for gear shifting; 3. Prevent overload of the transmission system; 4. Reduce torsional vibration impact from the engine and extend the life of the transmission gears.
I've been driving manual transmission cars for ten years and have encountered similar abnormal noises. When idling, there's noise, but it disappears as soon as I press the clutch. This is mostly a problem with the clutch release bearing. When the car is idling, the engine drives the flywheel and the transmission input shaft to engage, and the bearing keeps rotating. If the bearing is worn or damaged, it will make a squeaking or buzzing sound. After pressing the clutch, the release bearing stops rotating, and the noise naturally disappears. This is not a trivial matter. If ignored, the bearing may completely fail, leading to difficulty in shifting gears. Long-term driving in high-temperature environments or using older cars makes this problem more likely to occur. It is recommended to go to a repair shop for inspection as soon as possible. Replacing the bearing usually costs a few hundred yuan. Don't wait until the noise gets louder to fix it, otherwise, you'll have to spend more money replacing the entire clutch system.
From a mechanical perspective, a manual transmission car making abnormal noises at idle that disappear when the clutch is pressed usually indicates a worn release bearing. This bearing rotates with the input shaft at idle, and when worn, the friction noise increases; pressing the clutch disengages the bearing, stopping the noise. Other possibilities include a loose flywheel ring gear or input shaft bearing issues, but the release bearing is the most common culprit. If you notice the noise only at idle, especially more pronounced after a cold start, it's highly likely the bearing is aging. The repair is straightforward—have a mechanic diagnose by sound and check if the transmission fluid is sufficient. Degraded fluid can also accelerate wear. Develop the habit of avoiding unnecessary clutch pressing at idle to prolong its lifespan. Ignoring the issue can lead to worsening noise, affecting normal driving safety.
