Ball joints allow the steering knuckle to pivot for steering while providing a tight connection to the control arms and preventing any unwanted up and down or sideways movement. Ball joints use a ball-and socket joint to allow a wide range of motion, similar to a shoulder or hip joint. An illustration of a ball joint is shown in Figure 6-27.
Ball joints can be one of two types, load carrying or non-load carrying. Load-carrying ball joints support the weight carried by the springs. Because of this, these joints tend to wear faster and need replacement more often than non-load-carrying joints. Non-load-carrying joints provide a steering pivot and component connection with a wide range of movement just like load carrying joints, but without the sprung weight applied to them. Figure 6-28 illustrates how weight is carried by a ball joint.
Ball joints are mounted to the control arms in a variety of ways. The most common ways are a press fit, bolt in, and rivets. Some older vehicles had threads on the ball joint itself, which was then threaded into the control arm. Joints that are riveted at the factory are replaced with joints that bolt into the control arm. Some heavy-duty and older vehicles use kingpins instead of ball joints. A king pin connects the steering knuckle to the front axle. King pins and king pin bushings do not use a ball-and-socket joint; instead, the king pin is pressed into the bushings. The king pin rotates in the bushing to allow for steering movement.
