Ball joints are a vital part of a car’s suspension and steering systems. They connect the wheel hub to the vehicle’s suspension. The ball joints are able to move horizontally and vertically and to rotate, allowing the car to be steered and providing shock absorption for a comfortable ride.
The ball joint consists of a polished metal ball encased by a polished metal cage, with a rubber boot covering the joint to keep the grease in and any dirt and other impurities out. Ball joints are almost always used in the front suspension only, although, in some high performance cars, they are also used in the rear suspension.
Cars can have two or four ball joints on the front wheels. If the car has McPherson struts, it only has two ball joints, which are positioned at the bottom of the wheel hub. If it has shocks and springs, it has both upper and lower ball joints. Some ball joints are load bearing, carrying the car’s weight, whilst others are non-load bearing.
Ball joints do wear over time, especially load bearing joints. If the rubber casing fails and grease leaks out or dirt gets into the joint, wear is likely to be accelerated.
Signs of a failing ball joint are the presence of a banging sound when the car goes over a bump, sloppy or stiff steering, a vibrating steering wheel or tyre wear on the outer or inner edge of the tyre.