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The Basics of Four Wheel Alignment Service

by Steve Cartwright

Alignment checks are recommended by most vehicle manufacturers at specific mileage or time intervals, or whenever steering, suspension parts, or some front-wheel-drive (FWD) driveline components are replaced. Alignment also is recommended when new tires are installed, or when customers complain of pull or abnormal tire wear such as scuffing, cupping or more accelerated wear on one side of the tire.

The type of alignment performed usually is conditional upon the amount of adjustment that's feasible on a particular vehicle, as well as the shop's equipment capability. On solid-axle, rear-wheel-drive (RWD) vehicles, for example, a thrust alignment is usually performed so the front wheels are aligned to the rear axle. The drive direction of the rear axle is referred to as the thrust line, which should in theory be the same as the geometric center of the vehicle.

A four-wheel alignment involves adjusting the rear wheels to achieve proper camber and toe and a thrust angle as close to zero as possible, then adjusting the front wheels to the same vehicle centerline. Four-wheel alignments are recommended for most front-wheel-drive cars, mini-vans, some sport utility vehicles and RWD vehicles with independent suspension.

Many alignment shops today offer a standard thrust alignment and charge extra for time and materials if rear-wheel adjustments are required. This approach eliminates different vehicle owners paying the same price, when only one of them requires rear-wheel alignment.

Equipment requirements
To perform a four-wheel alignment, a four-sensor machine is required. Turnplates or rear slip plates at all four corners are needed during both four-wheel and thrust alignments. The rear wheels must be allowed to relax to their normal position to achieve proper readings whether they are to be adjusted or not.

Today's computerized alignment equipment can identify and graphically display the alignment capabilities of a vehicle by make and model. In addition, the machine will do all the mental gymnastics of shim selection and orientation, which leaves the technician free to do what he or she does best - diagnose and correct the alignment problem.

Some newer model alignment machines feature cordless sensors that use high-frequency transmitters instead of cables to send data to the console. Other new features include a ride height option that shortens measurement time to just a few seconds per wheel and provides on-screen videos to illustrate the adjustment method on the vehicle being serviced. Some machines use a laser, similar to a pointer, for toe measurement.

In addition to providing caster, camber and toe readings, alignment machines can be used as a diagnostic tool. Diagnostic angles such as steering axis inclination (SAI), included angle (IA), setback and turning radius can help the technician to identify problems that otherwise might be overlooked.

Both SAI and IA are measured similar to a caster sweep. When the SAI reading is combined with the camber reading, the sum of the two angles equals the IA. Using SAI/IA and camber will help identify a bent or shifted component.

The optimum setting on all vehicles for setback is zero, so either a positive or negative setback reading indicates cradle shifting or some other component has moved.

Turning radius, also referred to as toe-out on turns, is determined by the steering arms relative to the lower steering pivot. When the vehicle is steered into a turn, the steering arms cause the wheels to turn at different angles, creating a toe-out condition. If the turning radius is incorrect, inspect the steering arm and lower steering pivot components for damage.

A potential bump steer problem can be spotted by setting the alignment machine to its toe screen, then jouncing the vehicle's suspension while observing toe change. The toe reading should move positive or negative equally, or remain unchanged. If the reading shows one side positive and the other side negative, or a dramatic difference side to side as the vehicle is jounced, check for a bent pitman arm, idler arm, steering arm or centerlink, firewall damage, or a shifted engine cradle or worn rack-and-pinion mounting bushings.

Using the turnplates on alignment equipment, a technician can check for a bent steering arm by measuring the amount of toe-out on turns for each wheel and compare them.

Height must be right
Some of today's alignment equipment also can diagnose ride height, which is critical to proper alignment and suspension geometry. Ride height is the angle that all wheel alignment angles are built around and should be kept within manufacturer specifications for optimum performance of the entire steering, suspension and driveline system. XXVehicle modification is another area of concern. When vehicles have been modified from the manufacturer's original design, factory alignment settings may no longer apply. Aftermarket wheels may have different offsets than the original wheels. Altering tire sizes may upset the spindle's distance from the ground, which can have an effect on scrub radius. Raising or lowering vehicle height may alter the suspension and steering systems' geometry during deflection and cause excessive toe change or stress some parts beyond their limits.

Weak, sagging springs can force the entire steering and suspension system to go out of proper alignment, which spells problems for any vehicle. A correct alignment with a sagged suspension can still produce tire wear and handling problems during dynamic operation.

With the sensors attached to each wheel, raise the vehicle under the frame or unibody to the correct height and observe the readings. If the alignment problem is solved, repeat the demonstration for the vehicle's owner and recommend spring replacement.

Air and hydraulically suspended vehicles may have a specified procedure that is necessary to achieve the correct alignment height prior to adjustment. On some air suspension systems, it is first necessary to allow the air in the air spring to reach shop temperature prior to alignment.

If a large difference exists from the shop temperature to the colder outside air, the vehicle height can change during alignment, affecting the readings as the air in the bladder expands. Coil springs are available to replace leaking or failed air spring suspensions on applications such as the Lincoln Town Car, Mercury Grand Marquis and Ford Crown Victoria.

Failure to detect incorrect chassis height can often lead a technician to a wrong diagnosis, such as attributing the lack of adjustment range to a bent frame.

Diagnosing component wear
Tire, brake and driveline problems are often mistaken for an alignment problem by the vehicle owner, so the customer should be consulted as to what made them think the vehicle needs aligning. Begin by asking the customer a few simple questions, such as: What is your vehicle doing to make you think you need an alignment? Does it pull? When does it pull? Is the steering wheel straight? Are the tires worn unevenly?

Next, verify the problem with a test drive and a complete inspection of the tires and the wear patterns they display that indicate a steering or suspension problem. If the customer is getting new tires, examine the old ones for unusual wear before they come off the vehicle. Explain to the customer how new tires will experience the same wear as the old ones unless the underlying cause of the problem is corrected.

If a loose steering or suspension part is discovered, show the customer the actual problem. If possible, demonstrate a properly functioning part on a similar vehicle in the shop for comparison. Due to the hectic schedule in most shops, this step is sometimes overlooked even though people learn best from hands-on experience.

It's essential to always be precise when discussing factory specifications for steering and suspension components. Some chassis parts must exceed a listed tolerance for looseness to actually require replacement. In many cases, the part can be within its tolerance range but still contribute to tire wear, alignment and handling problems. XxBall joints sometimes have looseness tolerances as high as 1/4-inch before replacement is required. Some amount of looseness within this spec could create problems for the driver of the vehicle, but the replacement is not required until the tolerance is reached. XxWhen making a service suggestion to the customer, explain that although the ball joint may be within its listed tolerance, the looseness could allow wheel movement and create alignment angle changes. A part that is loose, but still within its listed tolerance, should never be described as bad.

Some steering components such as tie rod ends may not have a listed tolerance. Inspection of these components may rely entirely on the technician's judgment, using hand pressure or some other approved method as a measure of excessive looseness.

General guidelines for determining when to make replacement suggestions to customers are provided by Motorist Assurance Program (MAP). The Web site address for MAP is www.motorist.com.

Performing the wheel adjustment
Vehicle manufacturers determine which angles are adjustable from the factory based on need and feasibility. Various adjustment mechanisms such as shims, cams, threaded rods and slotted frames usually provide enough adjustment, providing height is correct, to bring the vehicle into specification.

With some newer alignment machines, the technician no longer has to struggle with calculations, or perform trial-and-error installations to decide which shim to use, or how it should be installed. Modern alignment equipment automatically calculates the desired amount of correction, selects the correct shim and displays its orientation on the screen for the technician. This makes installation quick and virtually error-free.

In recent years, however, vehicles without full alignment capabilities have been showing up in alignment shops. A common error among some technicians is to assume that a vehicle without enough adjustment range has a bent frame.

Especially on smaller cars, some angles are not factory adjustable and may require an aftermarket modification to bring the vehicle into specification. Ford Escorts and Mercury Tracers, for example, feature two rear wheel control arms. On earlier models, only one of the control arms is adjustable for toe, while the other isn't. The one OE adjustment allows a total toe adjustment, but will not provide the individual wheel toe adjustment necessary for a four-wheel alignment.

This problem can be corrected using a specially designed eccentric control arm bushing kit that, when installed, will enable toe adjustment on both sides of the vehicle. Relatively easy to install, the kit will allow individual toe adjustment for optimum tire life.

Toe and camber adjusting shims are available for some front-wheel and many rear-wheel alignments. The glass-filled nylon shims are made to very close tolerances to provide a range of adjustments. Rear alignment shims are tapered so they can be rotated to provide a different thickness at the top or bottom of the wheel to align camber, or to change toe, or to do both simultaneously, depending on what the vehicle requires.

Other alignment products include camber/caster adjusting sleeves, cam bolt kits, offset shaft kits and offset bushings for camber/caster change on front suspensions and toe adjustment on some rear suspensions.

Technicians are cautioned that elongating holes or making other modifications not specified by the manufacturer can lead to safety concerns and undesired movement after the vehicle leaves the shop. Only use alignment kits from a reputable source and don't arbitrarily elongate a hole because it seems like a good idea.

Other common alignment errors to avoid include:

• Failing to perform an accurate vehicle inspection, including height measurement, to assure a quality alignment. Rushing to see how many alignments can be done in a day can lead to missing valuable sales, tire adjustments and customer comebacks.
• Failing to pull the rear turnplate pins during a thrust alignment.
• Overtorquing rear hub attachment bolts, causing possible full or partial contact shim deformation.
• Sweeping caster at the tire instead of the steering wheel, causing vehicle movement on the turnplates that can affect the accuracy of the readings.
• Remembering to inspect the vehicle for the presence of a rear shim prior to cutting a new one.

In cases where it's necessary to do an alignment where loose, yet safe, parts exist, always note on the repair order that tire wear and handling problems may occur. Encourage the customer to come back by offering to check the alignment again for free once you complete all of the necessary repairs. This will be an incentive to complete the rest of the repairs when money is available.

Steve Cartwright is a Master Automobile Technician, a Master Heavy-Duty Truck Technician and is certified in four auto body specialty areas. For testing and certifying in 16 testing categories, he has been recognized as an ASIA/ASE World-Class Technician. He is a master instructor with the Moog Automotive World Training Center, St. Louis, Mo., and worked previously at a Ford dealership.