The interaction between the input and output shafts in your manual transmission vehicle is critical to keeping it in gear while driving. The slightest damage to the input shaft could have major consequences for the engine, as well as the transmission. Because of this, it is important for drivers to recognize the symptoms of a bad input shaft bearing.
Strange Noises in Neutral
When your vehicle is in neutral, you should only hear the hum of the engine. But, if you hear strange noises before you put the car in gear, it is most likely a sign of a faulty input shaft bearing. The tone and pitch of this noise will vary based on the speed that the engine is running at. If you hear these noises while in neutral, you might also be able to feel a vibration in the gear stick. If you are experiencing this, you should change or refill the gear oil to see if this eliminates the problem.
Persistent Noises From the Gears
Strange noises coming from under the hood are never a good sign, and this is especially true when they are coming from your transmission. Another sign of a failing input shaft bearing is hearing even more noise when you put the car into drive. Like the noises when in neutral, these sounds only get louder as the engine puts out more RPM. You can identify the problem as the input shaft because the noise will continue while the car is stopped, whereas the noise would stop along with the vehicle if it were an output shaft issue.
Sudden Gear Slips
The most worrisome symptom of a bad input shaft bearing is the vehicle suddenly shifting gears when stepping on the clutch. The failure of the input shaft bearing allows the shaft to have too much movement, which creates problems with gear shafts not being properly aligned. This leads to your car slipping between gears, potentially causing considerable damage to the vehicle.