The humble ball joint took the place of the kingpin in front suspension systems during the 1950s. What makes the ball joint a great invention is its ability to articulate around two planes of movement. If you have two of them in upper and lower form, they can articulate around three planes of movement. A ball joint is a simple ball and socket arrangement on a par with the human hip or shoulder joint.
The ball and stud move around inside a stationary socket. The ball is tied to a steering knuckle or spindle that steers right or left. When you have an upper and lower ball joint, not only do they move with a spindle, they move up and down with the suspension. Installations with McPherson strut dampening generally have one ball joint at the lower control arm.
Because there's such a huge variety of front ends out there, it is impossible to show you all of them. However, we can talk about some of them. Because ball joints and suspension bushings generally wear out at the same clip, it's a good idea to replace both at the same time if for no other reason than to maintain a stable alignment. Older Ford and Mercury compacts and intermediates have a coil-over-upper arm suspension system.
This approach began with Falcon and Comet, Fairlane, four-seat Thunderbirds, Mustang and Cougar, Torino, Cyclone, Maverick, Granada and Monarch ending in 1980. There are still a lot of vintage Fords and Mercurys out there with this suspension system.
When it's time for ball joint and bushing replacement, it is often easier to replace the entire control arm. New upper and lower control arms generally come complete with both ball joints and bushings. Some control arm assemblies have non-serviceable ball joints, which means the arm must be replaced. Older Chrysler products have screw-in lower ball joints that are easy to replace.