Bearings are what allow the gears to rotate efficiently. They are typically built away from bronze or brass, they usually in shape into races (or grooves) within the gearbox housing. Tough shifting, diminished gas efficiency, and burning smells are just a number of the signs of a nasty transmission filter. https://filtergearbox90753.dm-blog.com/34114755/the-fact-about-filter-gearbox-that-no-one-is-suggesting