Transmission fluid is a thick liquid that lubricates the moving parts of your car's transmission. Manual transmissions can use different types of fluids: regular motor oil, hypoid gear oil or automatic transmission fluid. In most cars, the fluid should be changed every 30,000 to 60,000 miles; however if you subject your car to heavy-duty use, the fluid should be changed every 15,000 miles. It is important to check your transmission fluid between changes because symptoms of low fluid levels often appear after damage has already been done. Ask your mechanic to check the levels at every oil change.
If you notice a leak under your car's gearbox, it is likely that your transmission is leaking fluid. Unlike automatic transmissions which always use transmission fluid that is pink in colour, different types of manual transmissions require different types of fluid. Therefore, you cannot rely on colour alone to determine the source of the leak. Consult your mechanic if you notice a fluid leak.
Problems Shifting Gears
If you experience difficulty shifting gears, it could be because of low transmission fluid. In this case, you might feel like that the shifting is more difficult and stiffer than normal.
Low transmission fluid can cause your manual transmission to make a noise either while in neutral or while in gear. Because other transmission problems such as worn gears and shafts can cause the same symptoms, have your car checked by a mechanic.
If your gears make a grinding noise during shifting, check the transmission fluid. This symptom can be caused by other problems such as a faulty clutch, a defective synchroniser or a stuck gear.