Ball Joint Buyer's Guide

Where Are Ball Joints Located?

• Control arms: Most notably, ball joints are found at the connection point between control arms and the steering knuckle. Your suspension design determines the number of control arms and therefore the number of ball joints. In a double wishbone suspension, as seen in the diagram below, there will be a ball joint present on both the upper and lower control arm.

• Tie rod ends: The outer tie rod end uses a ball joint to connect to the steering knuckle, allowing for movement as the suspension travels and the wheel steers.

• End links: Depending on the design, sway bar end links may use ball joints to connect the sway bar to the control arm.

How Ball Joints Work

A ball joint consists of a ball stud (the moving part), a plastic or metal bearing insert that the ball rotates within, a housing that holds the bearing, and a rubber boot that seals out dirt and debris. The bearing insert allows the ball to rotate and articulate smoothly. The rubber boot protects the bearing from contamination, extending its lifespan. Some ball joints include a zerk fitting (a small nipple where you can attach a grease gun) which allows you to inject fresh grease. If your ball joint includes a zerk fitting, greasing it periodically with a grease gun will significantly extend its service life.

Load-Carrying vs. Follower Ball Joints

Ball joints come in two types, each designed for different loads.

• Load-carrying ball joints support the vehicle's weight and are found on lower control arms.

• Follower ball joints are found on upper control arms and outer tie rods. Follower ball joints are not designed to bear load and will fail if used in a load-carrying position.

Spherical Bearings

For dedicated track cars, you may consider upgrading to spherical bearings. Spherical bearings replace ball joints with a precision design that completely resists deflection under load. They offer maximum precision and allow you to maintain consistent suspension geometry at all times. While spherical bearings are great choices for dedicated track cars, they are poor choices for a street car because they transmit significant noise and vibration to the cabin and have much shorter lifespans (typically 10,000-20,000 miles).

Conclusion

Ball joints are wear items that eventually require replacement as suspension cycles over tens of thousands of miles. When replacement is needed, decide whether you will replace the entire component or just swap out the ball joint. For outer tie rods, it often makes the most sense to simply swap out the entire tie rod. For control arms, either option is appropriate. If you are replacing just the ball joint, you will need a ball joint press.

For street vehicles, factory-equivalent ball joints are the right choice. If you are building a track car, consider using spherical bearings for maximum performance. You can find all the parts you need and plan your build on RideBuilder.

Additional Resources

• Tie Rod Buyer's Guide

• Control Arm Buyer's Guide

• End Link Buyer's Guide