The most commonly misdiagnosed condition following a collision repair is often alignment related, according to Mark E. Olson, chief operating officer for Verifacts Automotive, and the reasons why are prevalent both inside collision repair shops and shops specializing in alignment.
Olson, who is also a regional trainer for Hunter, got right to the point in his Friday afternoon session “Alignment Expert in 90 Minutes,” moving past the caster and camber reds and greens on an alignment spec sheet, and circling the steering axis inclination (SAI).
“SAI is the most important number on the sheet,” Olson said. “Lack of understanding [this about SAI] creates unnecessary parts replacement and improperly repaired vehicles that do not drive correctly.”
To find the cause of the pull, you first need to locate the SAI. SAI comes from the angle between the upper pivot point and the lower pivot point of a strut at the front of a vehicle. Olson said a vehicle will pull to the side with the least amount of SAI, generally anything that is a degree or more.
With the SAI numbers in hand, you can start to rule our certain alignment problem culprits. Olson likened true alignment diagnosis to a math equation. For example, according to Olson, if the SAI numbers are the same for both sides, you know there is no frame damage and you don’t need a lower control arm — instead turn to the strut or the knuckle. If the SAI is within spec and the caster is in spec, the cause of the problems is likely a ball joint.
After the SAI, also become familiar with the included angle and start looking at both of these figured before you even look at the caster, camber, tow numbers.
Other quick notes Olson expanded on within the longer presentation:
• Ride height affects everything. A change in ride height will mess with all of your alignment angles.
• Toe does not cause a vehicle to pull. This will cause a dogtail and potentially tire scuffing, but tow correct toe alone will not affect pull.
• Camber tipping in will wear the outside of a tire, tipping out will wear the inside.
• It’s only a four wheel alignment if you end up adjusting the rear. Shops get in trouble for charging for a four-wheel alignment if after the procedure only the front wheels have been adjusted.
• Remember that caster affects directional stability. If a customer is still complaining of driveability problems, and everything seems to be checking out on the sheet, the caster may be off just enough to effect cornering, depending on the vehicle.