LEGO MOC 6-Speed Synchronized Gearbox by DGustafsson13 by DLuders | Rebrickable - Build with LEGO
Never really built a gearbox before but knew the basics of a 2 and 4 speed boxes so i smashed them together and build this kinda small 8 speed gearbox : r/legotechnic
Video: Check Out This Working Six-Speed Gearbox Made of Legos - TeamSpeed