LEGO MOC 6-speed sequential gearbox by Whathetech | 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
Lego Technic 2 Speed Transmission - Instructables
Lego Technic Multi Function Gearbox with Build Instructions - YouTube