Dial indicator positioned to measure rotor runout.

Automotive steering and suspension systems rely on tight components to ensure proper handling and maximum tire life. As the vehicle gets older, some of these critical components wear and should be inspected for looseness.

Ball joints are suspension components that must be inspected at some point on an automobile. Measuring ball joints for movement or checking tires for radial runout are two tasks that technicians should perform often. Many times these tasks are checked using the "eyeball method" - not the appropriate tool. More and more, the professional technician needs to use tools like gauges or dial indicators to ensure accurate measurements. These measurements of worn or damaged parts can then be documented and compared to vehicle specifications. This policy gives added credibility to the technician when recommending parts replacement.

This article will deal with types of movement terms - lateral, axial and radial. These types of movement can be confusing, as they are not always described the same way. They are described differently on different components. As an example, axial movement of a ball joint is movement up and down. At the same time, radial movement or runout on a tire could also be up and down movement. This article addresses some of the terms used when measuring looseness or movement of components.

Lateral movement:

Lateral movement is perhaps the easiest to describe. This type of movement is always side to side. This side-to-side movement can be demonstrated when measuring disc brake rotor runout on the vehicle. Another example of lateral runout would be on a tire where an indicator is set up to measure the movement on the sidewall of a tire.

Axial movement:

This photo shows a dial indicator installed to measure axial movement on an input shaft of an automatic transmission.

The base word of axial is axis. Axis is something on which an item turns or rotates. The earth is a good example. It rotates on an imaginary axis. A bench grinder is another example where the shaft is horizontal and rotates around bearings. Axial movement is movement along the axis or centerline of a part or component. The axial movement of a bench grinder would be movement along the center of the shaft. Standing in front of the grinder, this would be movement side to side.

Another example is a rear wheel drive axle that can be moved in or out toward the differential. This movement would show axial movement. Axial movement on a ball joint means looseness or movement that is in line with the ball joint stud and in this case would be considered up and down movement. This imaginary line that travels from the center of the lower ball joint through the upper ball joint is often referred to as the steering axis. It is the pivot that allows the front wheels to steer left and right.

It is important to understand that axial movement is not always up and down. It depends on what you are working on.

Radial movement:

This image shows the dial indicator positioned to measure radial movement on an axle flange.

Radial movement is movement perpendicular or about 90 degrees to the axis.

Most people have grown up hearing about radial runout and maybe not really knowing what the term meant. Radial is also a common term when referring to tires. Some might think that the radial runout on a tire refers to radial tires. However, you can measure radial runout on a bias ply tire and in fact, radial runout can be measured on about anything. Some radial runout is up and down movement and some radial runout is side to side. I first realized this when taking ASE tests. A couple questions dealt with radial runout. The question asked if radial runout on a ball joint was side to side and radial movement on a tire was up and down. The answer is true. This is an example of why technicians need to know the difference between axial movement, radial movement and lateral movement.

Radial runout gauge in positioned to measure radial runout on the tread of a tire.

It is important to remember that ball joints should be checked for looseness in any direction, both up and down and sideways. Optimum safety and handling characteristics are achieved only when the steering and suspension components are tight.

Radial movement:

Radial runout of a tire places the dial indicator to read a measurement on the tread of the tire. This activity will determine if the tire is out of round. The concentricity or roundness of a tire must be within certain specifications or it obviously will cause a vibration as it travels along the road.

Unloading the ball joint:

It is important that when checking looseness on a non-wear-indicating ball joint, the weight of the car is not on the joint. This is commonly referred to as unloading the ball joint. This practice is necessary to ensure the force of the springs is not applied onto the ball joint. It is important to understand that if the ball joint is not properly unloaded, it could mistakenly be determined as satisfactory when in fact, it should be replaced.

Wear-indicating ball joints:

Line drawing of a wear indicator ball joint.

A wear-indicating ball joint should be checked with the vehicle weight on the joint. In other words, lifting the vehicle is not required and the ball joint can be inspected with the vehicle on the ground.

There are two styles of short and long arm suspension (SLA); each is treated a little differently when removing the spring tension from the suspension to unload the ball joint.

Proper service manuals with exact procedures and safety instructions should always be observed. Hopefully, next time the terms axial, radial and lateral are used, you will be more aware of what they actually mean.

Rod Collard is an associate professor in the Automotive Technology program at Southern Illinois University at Carbondale, Ill. He is ASE master certified in the areas of Automobile, Heavy-Duty Truck, and Auto Body and Paint.

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