What causes the abnormal noise in manual transmission at idle that disappears when the clutch is pressed?
3 Answers
Manual transmission at idle has abnormal noise that disappears when the clutch is pressed because: There is an issue with the car's clutch release bearing, and it is recommended to replace the release bearing. The clutch is located inside the flywheel housing between the engine and the transmission, and the clutch assembly is fixed to the rear plane of the flywheel with screws. The output shaft of the clutch is the input shaft of the transmission. The main functions of the clutch are: 1. To ensure smooth starting of the car; 2. To achieve smooth gear shifting. A manual transmission car refers to a car that uses a manual shift mechanical transmission to adjust the speed. The gear meshing position inside the transmission is changed by manually moving the shift lever to alter the transmission ratio and achieve the purpose of shifting gears.
I've been repairing cars for over 20 years and often encounter this issue. When a manual transmission makes a buzzing sound at idle that disappears when the clutch is pressed, it's usually a problem with the clutch release bearing. That bearing is located inside the transmission housing and normally rotates against the pressure plate. When worn, it produces abnormal noises. When the clutch is depressed, the release bearing is fully compressed and becomes quiet. It could also be due to aging of the transmission input shaft bearing, which vibrates and makes noise at idle but stops when the clutch cuts off power. Another possibility is damage to the flywheel pilot bearing. The tricky part is that all three issues require transmission disassembly for inspection. I recommend repairing it as soon as possible, otherwise wear debris may damage other components, leading to higher repair costs later.
Last time I drove an old manual car on a long trip, I encountered the same issue—a whining noise from the chassis at idle that immediately went quiet when I pressed the clutch. The mechanic opened it up and found the release bearing worn down like sandpaper. The principle is simple: at idle, the release bearing lightly touches the rotating pressure plate, and when the bearing is worn, it squeals; pressing the clutch pushes the bearing all the way down, eliminating the gap and stopping the noise. Also, check the transmission oil—low or degraded oil can cause the bearing to fail prematurely. Remember, never use high-viscosity engine oil as a substitute for gear oil, as the wrong viscosity can accelerate wear. After replacing the bearing and transmission oil, the car became much quieter immediately.
