Bearings are what allow the gears to rotate effortlessly. They are usually built from bronze or brass, they usually in good shape into races (or grooves) inside the gearbox housing. Really hard shifting, lowered gas efficiency, and burning smells are only some of the indicators of a foul transmission filter. https://filter-gearbox65308.boyblogguide.com/33109388/not-known-facts-about-filter-gearbox