Understanding ball joints and how to check them is an important part of every safety inspection. If the control arm transfers the load directly to the suspension spring, the ball joint of that arm is a loaded ball joint because the weight of the vehicle is transferred through it to the spring. Any remaining joint is considered a follower joint, which simply serves as a pivot point.
There are many different suspension designs, which change the location of the loaded or follower joints, and a typical stretched suspension has only one follower joint on each side, since the weight of the vehicle is transferred through the direction to strut and spring. . It is important to identify the type of joint so that you can also identify the appropriate method of inspection. When checking ball joint wear, how you lift and support the vehicle or suspension will affect the result.
An example is this typical SLA suspension where you need to unload the suspension by lifting the vehicle under the lower control arm, or the spring tension will prevent any play in the joints from being detected. Another example is this SLA suspension with the coil spring over the top arm, and you have to raise the vehicle up the frame. And in a typical strut suspension, the vehicle must also be supported by the frame. In addition to proper support, you can check them by hand or you may need to use a pry bar, and you should always use a dial gauge to determine the amount of free play.
It’s a common misconception that any free play means a bad ball joint, but depending on the type of joint, some may be acceptable, and some joints use grease position as an indicator of wear. The bottom line is to always check the manufacturer’s specifications and specific inspection procedures to make sure you’re doing the job right.
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