Many parts professionals remember the days when the “factory” shock absorbers were routinely replaced after only 5,000 or 10,000 miles of use. Ball joints would occasionally fail before 30,000 miles and just about any suspension or alignment parts could be expected to wear out after that. Because of that era’s lower life expectancies for suspension and alignment parts, the “wheel alignment” business boomed from the 1950s through the 1990s, when auto manufacturers began engineering more durable and sophisticated suspension and alignment systems.
But time and technology have changed the suspension and alignment parts markets. The metallurgy, lubrication and sealing of suspension and alignment parts have vastly improved during the past decade. In addition, vehicle chassis are being manufactured to much more precise tolerances, which reduce alignment and handling complaints. Nevertheless, all moving parts eventually succumb to normal wear and collision accidents continue to fuel the demand for suspension and alignment parts.
SUSPENSION AND ALIGNMENT DEFINITIONS
Although the functions of suspension and alignment parts are interdependent, it’s important to understand which parts are suspension and which are alignment. In brief, suspension parts are those parts responsible for mounting the axles and wheels to the chassis. Suspension parts include McPherson struts, shock absorbers, springs, and the load-bearing ball joints and control arms. Alignment parts, on the other hand, are those parts responsible for steering the vehicle. Included are tie rods, tie rod ends, tie rod connecting links, rack-and pinion steering gears, conventional steering gears, idler arms, and the ball joints and pivot bushings located on the non-load bearing control arm of the vehicle.
Clearly, some functional overlap exists when classifying control arms, ball joints, steering knuckles, and axle linkages. In short, all of these parts are suspension parts in the sense that they attach the wheels and axles to the chassis. On the other hand, all of these parts help maintain the precise suspension geometry needed to keep the wheels aligned with the chassis.
ACTIVE SUSPENSION SYSTEMS
During the late 1980s, electronic ride controls were popularly introduced on some high-end luxury cars. In essence, these controls would maintain the correct ride height of the vehicle by inflating an air bladder located on the suspension system or shock absorber. In other types of systems, the driver could actually vary the ride control qualities of the vehicle by adjusting the firmness of the shock absorber as the vehicle traveled over the road. Today’s suspension systems still incorporate ride control and suspension height technology into modern accident avoidance systems.
ELECTRONIC ACCIDENT AVOIDANCE SYSTEMS
Today, most import and several domestic nameplates are either introducing vehicle stability controls (VSC) on their low-end vehicles or making them standard on their high-end vehicles. In addition, some are adding active cruise controls (ACC) to their safety menu. In any case, VSC will become standard equipment on most vehicles in the near future.
Needless to say, VSC will change how we sell suspension and alignment parts. Beginning with VSC, manufacturers have designed systems that are sensitive to drive inputs provided by various sensors, including the steering wheel position sensor, that detect abnormal “g-force” movements in the vehicle. In combination, these sensors detect emergency driving situations and are intended to help stabilize the vehicle by using the brakes to help steer the vehicle, using the ride control system to balance the vehicle, and using the electronic throttle controls to reduce vehicle speed.
Similarly, active cruise controls (ACC) incorporate a small radar emitter mounted in the front bumper that is intended to measure the distance between the vehicle and other objects in the roadway. When the active cruise control senses an impediment in the roadway such as a slower-moving vehicle, it will disengage the cruise control. In some applications, variations of this system will actually apply the brakes to prevent or reduce the effects of an impending collision. Although these systems are currently limited to high-end vehicles, the technology will trickle down to most popular nameplates.
Obviously, the old rules of selling suspension and alignment parts don’t apply in the modern world of VSC and ACC because these systems network with other on-board computers to fulfill their respective safety functions. In either system, the steering wheel and the wheels must be perfectly aligned with the chassis centerline in order for either system to operate as it was designed. In VSC, the brakes, springs, struts and shock absorbers must work as a system to stabilize the vehicle in an emergency situation.
Similarly, the ACC radar unit located in the front bumper must be aimed correctly with the vehicle centerline so that the radar beam can detect impediments in the vehicle’s driving lane. Here again, the ACC networks with the Powertrain Control Module (PCM) to avoid head-on collisions.
In either system, the drive axles and especially the steering wheel must be precisely aligned with the geometric centerline of the chassis. After each wheel alignment, a scan tool or the data processing computer in the wheel alignment machine must be used to “re-learn” the steering wheel position in relation to the vehicle’s centerline. If the axles, steering wheel, and radar emitter aren’t correctly aligned with the chassis’ centerline, a warning light might appear on the instrument cluster indicating a malfunction in either system.
Going back to selling suspension and alignment parts, it’s important to understand that suspension and alignment parts must work together as a system. If, for example, the pivot bushings in the axle control arms are worn, it’s nearly impossible to keep the wheels aligned with the geometric centerline of the vehicle. Similarly, if alignment parts are worn, it’s nearly impossible to keep the steering wheel aligned with the chassis’ centerline.
In contrast to earlier times when individual components were evaluated individually for wear, the concept of cumulative wear comes into play. To illustrate, if a single slightly worn tie rod end allows, let say, twenty one-thousandths (.020”) of an inch of toe angle variation, that amount of wear might be well within specification for a conventional vehicle. But, if four slightly worn tie rod ends allow a cumulative variation of eighty one-thousandths of an inch (.080-inch) variation in toe angle, then the cumulative variation might exceed specifications on VSC and ACC-equipped vehicles. Rather than replacing the most badly worn tie rod end, all four tie rod ends should be replaced to help keep the steering wheel aligned with the chassis.
Control arm pivot bushings play a similar role in keeping the axles aligned with the vehicle’s centerline. If the rear drive axle shifts position under load, it can no longer maintain a correct relationship with the chassis centerline. In that case, all of the rear drive axle pivot bushings should be replaced to keep the axle aligned with the chassis’ centerline.
To better understand how we should sell suspension and alignment parts, let’s look at how a master alignment technician might inspect a vehicle before he begins a wheel alignment. Because sagging springs will obviously change the suspension height and suspension geometry, the alignment tech will verify suspension height. The tech should also perform a rebound test on the struts and shock absorbers, visually check for fluid leakage, and check the strut bearing plates for return response at the steering wheel.
To avoid adversely affecting the VSC and anti-lock braking system (ABS) and tire pressure monitoring systems (TPMS), all four tires must be equal in size, pressure, and rolling circumference. The tie rod ends, ball joints, and steering gear will also be checked for abnormal wear. If worn components are found, replacement will be recommended.
Once the vehicle is mounted on the alignment machine, the tech will analyze the alignment readings to determine if the misalignment is caused by normal wear or by a collision situation. If, for example, the right front wheel is completely out of specification, the tech will test the steering knuckle against specifications to see if the knuckle is bent. The tech will also check the front and rear wheels for correct alignment with the chassis. If the wheels are out of alignment with the chassis centerline, the tech will check the suspension pivot points for wear and the control arms for bending or distortion.
The tech might also attach a scan tool to VSC vehicles to check for trouble codes and re-learn the steering wheel position after the alignment is completed. Once aligned, the vehicle will be test-driven to make sure that no diagnostic trouble codes are stored due to a steering wheel sensor misalignment or other electronic input malfunction. Each of these alignment steps represents a sales opportunity in suspension and alignment parts, so keep your pencil sharp and pay attention!
Gary Goms is a former educator and shop owner who remains active in the aftermarket service industry. Gary is an ASE-certified Master Automobile Technician (CMAT) and has earned the L1 advanced engine performance certification. He is also a graduate of Colorado State University and belongs to the Automotive Service Association (ASA) and the Society of Automotive Engineers (SAE).