Southeast dx7 is a South Korean Hyundai five-speed automatic manual transmission with model 4A9 1turbo. Gearbox is often called gearbox in cars; In industrial machinery, it is usually called gearbox, which is a mechanical or hydraulic device used for mechanical power conversion. Transmission is one of the main components of automobile transmission system. The actual use of the car is very complicated, starting, idling, driving at low speed or high speed, accelerating, decelerating, climbing and reversing. This requires that the driving force and rotational speed of the automobile can change in a considerable range, while the range of output torque and rotational speed of the piston engine widely used at present is very small. In order to adapt to the changing driving conditions and make the engine work in good working conditions (higher power and lower fuel consumption), a transmission is installed in the transmission system. Each gear has a different transmission ratio, which means that the meshing of the pinion and the large gear can produce different speeds. When driving at low speed, use low transmission ratio (3rd gear and below), and the spindle speed is lower than the engine speed. According to the formula P=FV, a larger driving force can be obtained. When driving at high speed, use high transmission ratio (4th gear and above), and reduce traction to get higher speed. When cutting gears, you can choose gears with different sizes to mesh with the gears of the big shaft.