LEGO MOC 2 Speed Gearbox by thatbrickguy | 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
Sariel.pl » 2-speed Automatic Gearbox
Lego 4-Speed Manual Gearbox | MOCHUB
Lego Technic video about Lego 2 Speed Automatic gearbox - worm gear prototype. Includes build instructions.