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
6 speed gearbox – Dgustafsson13
LEGO Technic 6 Speed Transmission Gearbox with V8 Engine - new parts | eBay
Lego 6 speed gearbox | 3D CAD Model Library | GrabCAD
Built Dgustafsson13's 6 speed Manual : r/legotechnic