It had been 1st introduced in 1939 for cars. It is made up of the fluid coupling and a few planetary gears. They collectively make three forward and 1 reverse speed. There's no clutch for engagement and disengagement from your motor. Bevel gearboxes have spiral and straight tooth shapes. https://gearbox82581.thenerdsblog.com/39565634/the-ultimate-guide-to-gearbox