Ball joints are an integral part of a vehicle's suspension system. They are flexible enough to allow the suspension system to move in multiple directions, and they assist in maintaining control over the front wheels. A ball joint is constructed much like a ball-and-socket hip joint. There is a rounded part that is designed to swivel inside of a cupped cavity, which allows for a broad range of flexibility in nearly any direction.
On most cars, there are two ball joints for each front wheel, and they are designed to last for a long period of time before needing service. However, they will wear out over time, and there are a number of signs that indicate that they are beginning to fail. When this component of the suspension wears out, the ball will not fit properly into its socket. Manufacturers typically account for some wiggle room, but too much wear will likely require replacement.
Another issue that can crop up is with the ball joint's lubrication. If the joint is improperly greased, it can cause excessive friction that may lead to premature failure. Most ball joints are equipped with special fittings that make it easy to add more grease without needing to take the suspension apart.
When the joints begin to wear, drivers may notice rattling or scraping noises coming from the front end of the car when driving over bumpy surfaces. Steering may become erratic as this part wears out, making it difficult to control the vehicle. This may point to a number of problems with the suspension, and in order to determine if the ball joints are to blame, the car will need to be jacked up.
Once this is done, first test the wheels. If they move around easily while the car is suspended, this can be a sign of worn ball joints.
Locate the ball joints under the steering knuckle, which is the part that connects the steering column to the suspension. On vehicles that have two joints per wheel, the lower joint will probably show signs of wear first, as it bears more responsibility than the upper joint. Check the rubber boots for damage - if they are torn or missing, this is a good indicator that the entire ball joint will need to be replaced. Signs of metal shavings or rust dust point to not enough lubrication.