The transmission shaft is composed of shaft tube, expansion sleeve (expansion spline) and universal joint, and the segmented type must be provided with intermediate support. The transmission shaft assembly is installed between the transmission and the rear axle to transmit the torque and rotary movement from the transmission to the final drive of the rear axle.

In the universal transmission device of steering drive axle, disconnected drive axle or mini car, the transmission shaft is usually made into a solid shaft. In order to obtain higher strength and stiffness, the transmission shaft is usually made into hollow (shaft tube is used to connect the universal joint and sliding spline). It is generally formed by rolling welding of thin steel plates with a thickness of 15-3mm. For super heavy trucks, seamless steel pipes are directly used.

The transmission shaft is the transmission shaft of the universal transmission device that can transmit power. It is a rotating body with high speed and few supports, so its dynamic balance is crucial. Generally, the transmission shaft shall be subject to dynamic balance test before delivery and adjusted on the balancing machine. For front engine rear wheel drive vehicles, it is the shaft that transmits the rotation of the transmission to the final drive. It can be several joints, and joints can be connected by universal joints.

The transmission shaft is an important part of the vehicle transmission system to transmit power. Its role is to transmit the power of the engine to the wheels together with the gearbox and drive axle, so that the vehicle can generate driving force.