Big Twin 4 speed transmissions have been built since 1936 in several versions. They were included on bikes with Knuckle engines, Pans, Shovels and some '84 and '85 Evolution 80's. They all used this transmission. With Andrews 4 speed gears, transmissions last longer, shift faster, and just plain run better. Bikes with Andrews gears feel so good that it’s hard to believe until you experience the difference for yourself.