When in first or second gear it sounds like the transmission is grinding. This only happens at low RPMs.
I am going to go ahead and move forward with the assumption that your Honda Civic is equipped with a manual transmission. I have owned Honda’s most my life and I have encountered this problem with the sound of transmission grinding myself more than once. As an experienced mechanic, test driving the vehicle would allow me to pinpoint the exact issue within a few minutes. However I am going to do my best to attempt to guide you in the right direction so you may at least have some idea of what is happening to your Civic.
The first culprit you will want to suspect for this grinding is a worn out clutch. The clutch and transmission get a lot of abuse, especially in densely populated areas of stop and go traffic. The clutch disc is a wear item, just like brake pads and spark plugs and like these parts, needs to be replaced. The clutch cannot be inspected without the removal of the entire transmission, so gathering as many facts as possible can help with accurate diagnosis. With your Honda being 15 years old, it would be important to know the mileage of the car and if the current clutch is original or has been replaced previously.
The second culprit I would suspect in your car is the syncro gears, which are found in the transmission. Syncros are designed to allow the engine’s input shaft to engage the gear you select, such as first or second. Both the input shaft and the gears are rotating at different speeds and the syncros allow them to join together, usually without grinding.
With this particular situation, taking into account that the grinding only happens at low rpms and 1st and 2nd gear, it is more likely you are experiencing the syncro problems I mentioned. Verification of this requires inspection of the entire transmission. During this process the clutch and supporting components will all be inspected for wear. This inspection consists of the labor to remove/install, disassemble/reassemble and inspect the transmission and supporting components. Once the tear down has taken place, the mechanic will know what component needs to be replaced and a quote for parts and labor usually follows.
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