Bearings are what enable the gears to rotate smoothly. They are usually created outside of bronze or brass, and so they in shape into races (or grooves) in the gearbox housing. Tough shifting, lowered gas efficiency, and burning smells are only some of the indications of a foul transmission filter. https://filter-gearbox67765.theobloggers.com/40354340/considerations-to-know-about-filter-gearbox