Since Ball joints are located under the car, it is not easy to see where they are and what condition they are in. For this reason, they are often forgotten about until they start causing problems. However, there are a number of signs to look for which could indicate a problem with the ball joints. Keep in mind that none of these definitely mean that the ball joints are bad; other problems with the suspension and steering can cause the same symptoms.
For most people, the first indication that they have a problem with their ball joints is a faint, intermittent banging sound that seems to be coming from a corner of the vehicle. This sound is usually more pronounced when going over a bump or dip, or when going around a corner. This sound is more like somebody hitting a piece of the metal structure with a hammer.
As time goes on, this sound becomes louder and more frequent. It is especially pronounced when the weight of the vehicle is transferred off and onto the wheel, such as when driving through a pothole , the sound of a worn ball joint can become a loud, creaking bang, similar to the sound of the bottom of the car hitting the ground.
Worn ball joints can affect the vehicle’s steering. This can manifest in a number of different ways, usually making the steering sloppy or stiff. If a vibration can be felt in the steering wheel when the vehicle is being driven down a straight, level highway, it could indicate a worn ball joint.
Another easy to recognize worn ball joints is uneven wear in the tires. If the outer or inner edges of the front tires are wearing faster than the rest of the tire tread, then there is a good chance that the ball joint is worn.
Checking the ball joints
If a ball joint is suspected of being bad, it needs to
be checked. This requires jacking up the vehicle so that the weight is off the tire and the wheel can move freely. Some try to check the ball joint without jacking up the car, but this only allows the upper ball joint to be checked, not the lower. Since more and more cars are being built with McPherson struts, this check is largely useless
Proper maintenance and replacement of a car’s ball joints is necessary for safety. Excessively worn ball joints can break, causing the wheel to collapse and control of the vehicle to be lost. However, the vehicle typically gives indications that the ball joint is bad long before a failure of this magnitude occurs.
reference: Ebay Mechanics