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 MOC 3-speed gearbox with comfortable manual step switch by Don_Santos | Rebrickable - Build with LEGO
LEGO MOC Lego Technic lockable automatic two speed gearbox [with free instructions] by SJ_LegoFan | Rebrickable - Build with LEGO
Moc High-tech Automatic Gear Change Version Of 2 Speed Gearbox Model Building Blocks Bricks Compatible With Pf Set Diy Toys - Blocks - AliExpress
LEGO MOC 2 Speed Automatic Gearbox - Smooth & Compact by TechnicBrickPower | Rebrickable - Build with LEGO