Why does the gearshift make noise without a synchronizer?
2 Answers
Without a synchronizer during gear shifting, the gear teeth tips collide, resulting in noise, difficulty engaging gears, and even gear grinding. Here are the relevant explanations: 1. Synchronizer: The synchronizer is an internal device in the transmission. When shifting gears while driving, it ensures smooth gear meshing. Some vehicles lack synchronizers, making gear shifting more difficult. 2. Function: Forward gears have synchronizers. When the clutch is depressed while the vehicle is moving and gears are shifted, the synchronizer automatically synchronizes the rotational speeds of the transmission's input and output ends. It ensures proper alignment between the teeth of the two gears (actually the spline sleeve and spline shaft) that are about to mesh, preventing tooth collision and noise during gear engagement.
I've been repairing cars for over twenty years and often encounter the issue of manual transmissions without synchronizers making constant noise when shifting gears. This is mainly due to the mismatch in rotational speeds between the input and output shafts during gear changes, causing the gears to collide directly and produce a 'clunking' sound. Without the buffering effect of synchronizers, you need precise operation—depress the clutch and wait a brief moment, allowing the engine speed to drop or rise to the appropriate level before engaging the gear. If the noise persists, it could be due to rushed operation or worn clutch plates not fully disengaging. I recommend practicing double-clutching techniques, such as blipping the throttle to match revs during downshifts. As the car ages, uneven gear tooth surfaces can worsen the problem. Regularly changing transmission fluid and checking for wear can help mitigate this; otherwise, prolonged forced shifting can accelerate transmission failure. Don't underestimate this noise—improper operation can easily lead to gear grinding and damage the gear set.
