Conditions when the car trouble occurs
When shifting into one particular forward gear grinding noise occur. However, the grinding sound is not heard when shifting into reverse gear.
Possible cause of grinding noise when shifting
The transmission gear synchronizer is defective
There is too much free play on the clutch pedal
Troubleshooting grinding noise when shifting
When the grinding sound happens only when shifting into forward gear the most likely reason for the problem is the component of the affected gear called the synchronizer. Synchronizer is a transmission component that brings the rotating shafts/gears together at the same speed when the car is running so that the shifting will become smooth. Now, if the synchronizer is defective you will hear a grinding sound every time you shift into the transmission into forward gear. When the defect of the synchronizer is severe the transmission is hard to shift or even worst, the shifting to another gear will become impossible.
If for instance the shifting problem occurs during shifting from a stop going into the first gear, it is most likely that the cause is related to the clutch pedal free play. Clutch pedal free play is the movement of the clutch pedal just before the clutch starts to disengage. When there is too much clutch pedal free play it can cause for the clutch not to be fully disengaged when shifting into first gear coming from a stop even when the pedal is fully depressed, if this happened there will be a grinding sound heard coming from the transmission every time the gear is shifted.
How to fix the grinding noise during shifting
Problem with the transmission is not an easy job it should be handled by mechanic that is specialized in transmission repair, therefore the only option you have is to bring the car to a reputable car shop that is expert when it comes to transmission repair.
Since the problem happened only when the shifting is done from stop going into the first gear the mechanic may only need to adjust the clutch pedal free play, or sometimes the mechanic will recommend to open the transmission in this case do not always agree with the mechanic recommendation seek first for a second opinion coming from another shops, if the other shop also recommend that the transmission is necessary to tear down then that is the time to agree for the transmission overhauling.