The Universal Joint (U-joint)

The Universal joint (U-joint) is used to connect the drive shaft to the transmission output shaft and the differential pinion gear shaft. This joint must be flexible enough to allow changes in the driving angle (road incline) and the drive shaft. This way, the torque is constantly transmitted when the rear axle is moving up and down. Smaller U-joints are used to route the turning motion of the steering wheel through the steering column to the steering box. There are two types of U-joints, the cross and roller type and the ball and trunnion type. The cross and roller type is used the most; it allows the drive shaft to bend. The ball and trunnion type less frequently used; it allows the drive shaft to bend and also permits backward and forward motion of the drive shaft.