However, when any vehicle is involved in an accident, extreme forces are placed upon the structure as well as related and/or attached systems such as braking, steering and suspension parts. When these systems are damaged from direct impact or secondary damage movement, we must be able to identify the damages early in the repair process to lessen delays in the completion of the vehicle. I am sure anyone would agree that finding out on the day of delivery that multiple special order parts are needed to get the vehicle wheel alignment within proper specifications or to drive properly is not a good thing. At this point no one is happy when it happens this late into the process.
It is true, repairers and insurers are involved in the process of returning the vehicle back to pre-loss condition as it relates to function and appearance. We must be very keen to determine if all damages caused from the accident are being repaired. This, today, can be very difficult to impossible by only an initial inspection, since the possibility of damages being masked by other parts is often present. This places an additional responsibility on the repairer, and even the technician, to identify these supplemental damages as early as possible, at least before the day of delivery.
This requires a high level of knowledge by all parties to understand what is required in the repair or replacement procedures of many vehicle systems. The suspension systems today are no different. The advanced electronic systems have diagnostic procedures that may use a troubleshooting flow chart, electronic test equipment such as DVOMs and scan tools. We need to embrace the fact that these tools are as necessary as hammers and dollies, plus they require training to properly use them.
Not all damages to an advanced suspension system will be obvious, such as broken or bent parts that are easily seen. If proper testing is not done on these systems to verify their proper operations, advanced functionality may be overlooked and damage could go unnoticed until the customer gets their vehicle back and drives it. Other than the obvious dissatisfaction of the customer having to return the vehicle for additional repairs, there may be safety issues in these critical systems, which may lead to extreme liability exposure for the shop and insurer.
Basic suspension systems
Even with all the advanced electronic functions, there are still basic suspension designs with which you must be familiar. The basic types of suspension systems used on vehicles all provide the same function. All systems are designed to handle the forces of braking, acceleration, dampening of road shock, handling the changes in road surfaces and turning during operation of the vehicle. The basic systems are:
- Short Arm — Long Arm System (SALA or SLA)
- McPhearson Strut
- Solid Axles
Today, there are many variations of these designs, but they still come back to the basic three origins. In addition, electronic sensors and controls to affect ride, braking, handling and feel are now often an additional consideration. It is important to consult manufacturer service manuals when working with these systems and get advanced training for them. Mistakes in this area can be very costly.
Diagnosing issues before they're issues
If visual inspection cannot uncover whether the suspension part is damaged, there are two basic options to look into further: comparative part measurement and quick checks and wheel alignment check diagnosis procedures.
Being able to measure a damaged part to an undamaged suspension part can be useful, but it is not always possible with two-dimensional measuring tools, such as tape measures or rulers. It's often impossible to get accurate readings, plus many of the critical comparisons are angles, not distance measurements.
However, within the last few years a three-dimensional measuring device has entered the market that is able to compare suspension parts within one millimeter and check angles of their mounts and arms at the same time. I have personally watched this system uncover damages to struts, spindles and lower control arms before installing them into the vehicle and just hoping they would take a wheel alignment. This system can also store known good measurements and angles for future retrieval. What a great concept — check the part before it is replaced and installed. Even better — check the parts before they are delivered or even ordered.
There are also times basic quick checks can be done to uncover damages that are not visibly obvious. These quick checks are taught in many I-CAR programs relating to damage analysis and suspension systems. These, again, are basic checks requiring minimal tools that may uncover issues related to damaged suspension parts. The scope of this article is not to review these quick checks. These are available through I-CAR training. The primary focus of this article is to look at how wheel alignment check information can provide the necessary basis to determine what is causing the real problem before throwing parts at it and moving or bending mounting areas that don't need to be moved or bent.
Symptoms are just symptoms
There are alignment angles and then there are alignment angles. Each angle has an important role in the handling of the vehicle, tire wear and fuel economy. Some of the angles represent symptoms and not what is causing the real problem, so fixing an angle that is not the real problem may add more issues to the vehicle while improperly fixing the angle that was just a symptom.
Most of us have heard the term "camber" — the inward or outward tilt of the wheel at the top, viewed from the front or back. This angle in most front and rear wheels needs to be checked and corrected within specification. It may or may not be adjustable. It is generally measured in degrees or fractions of degrees. As an example, if a line was drawn through the centerline of the tire (Figure 1), that line represents the camber angle compared to true vertical. If the tire is leaning out at the top (viewed from the front or back) it is called "positive camber" and if it is leaning in at the top then it is called "negative camber."Engineers determine what the camber angle should be at rest (static), to change during driving (dynamic), to maximize vehicle control and handling. Having all of the tires' surfaces on the road (0 degrees camber) during driving would be an ideal goal. This would minimize tire wear and vehicle pulling. Getting the camber angle to stay at 0 during all dynamic conditions is almost impossible since camber changes as the vehicle's height from the road surface changes. This height change is due to slight changes in the road, acceleration and braking. However, the more often it does stay at 0, the better the tire wear and vehicle handling occurs.
It is also very important that side-to-side (left to right) comparisons of the camber angles are balanced or within specifications given by the manufacturers. Generally, the collision repair industry should ensure this balance is within one-quarter of a degree side to side and each reading is on the same side of 0 (both negative or both positive). This is referred to as the "split" or "cross camber." Imbalance of camber readings out of specification can cause the vehicle to pull to the side of most positive (front wheels and opposite for rear wheels).
Keep in mind that out of specification camber is only a symptom for the real cause(s). Unfortunately, many parts are replaced, and adjustments may correct that camber, but not fix the real problem. It is important to understand which angles are which and what you can do to ensure they are corrected before it reaches the wheel alignment rack.
The most important angle — SAI
The first angle to inspect to ensure it is properly in specification is Steering Axis Inclination (SAI). SAI is defined as the inward tilt of the upper pivot point compared to the lower pivot point referenced to true vertical when viewed from the front or back (Figure 2). This is the angle created by a line drawn from point A through C and compared to true vertical. It is the primary directional control angle for today's vehicles. It is measured in degrees. There is no positive or negative because the angle must lean in toward the center of the vehicle.It is critical to look at the SAI readings for every collision-related alignment. SAI is the key factor in validating proper structural dimensions in suspension mounting areas during collision-related wheel alignments. Unfortunately, most alignment technicians that normally do retail alignments for consumers do not know how to run these angles properly. Each current wheel alignment system today has a very set procedure to perform these measurements. They are not automatic, but are clearly explained in the operation manual or help screens of today's alignment systems.
The main reason some don't know how to perform this measurement correctly is because normal retail outlets such as Firestone, Goodyear, etc., perform thousands more standard retail alignments each year than collision related alignments. They do not get into the habit of checking these important diagnostic angles. In fact, they may never have to. This is where they assume everything is correct. In a collision wheel alignment if they assume this, they may attempt to fix a symptom rather than the real problem.
It is also proper to mention that many alignment machines will provide an SAI reading while performing the typical caster sweep. This is where the wheels are turned in to a set amount and then turned out a set amount and the machine calculates the caster angle by how much the camber changes through the system's predetermined arc (sweep range). This is done with the suspension loaded and the wheels on the turntables. This is fine for the caster calculation, but not accurate enough for the SAI calculation. Proper readings for SAI are taken when the suspension is unloaded, and the vehicle must be level left to right. It is also important to keep the wheels from rotating through this measurement. The systems today generally have a separate area within the program to take these unloaded measurements.
Since a high percentage of front suspensions today are McPhearson strut suspensions, we are using this suspension type for this article, but much of the same logic is used for all suspension designs. If the structural repairs are completed properly, this angle will be correct unless the lower control arm is bent, ball joint stud is bent, or the engine cradle/crossmember has shifted side to side or is bent.
If the technician with even a tape or tram gauge verifies the relative lower ball joint position from side to side, makes sure the ball joint is not bent on either side, and the upper strut tower dimensions are the same left and right, then it is reasonable to assume the SAI readings will be the same left and right. On a symmetrical vehicle this means the structural dimensions for the lower and upper front structural relative to centerline are also most likely correct. When the vehicle is on the frame rack, it's definitely time to find out if a possible SAI alignment problem exists relative to the structural repairs. It is not when the job has been completed, painted and sent down to the alignment shop. So, making these checks with a measuring system is something that must never be overlooked.
However, what to do when the alignment guy tells you it won't align or the frame is still bent? The most important question to ask first is, "What are the SAI readings for both sides, and what are the caster and camber readings for both sides?" With or without specifications (many times SAI specifications are not published) this information can allow for a very quick diagnosis of the real problem.
If the SAI angles are the same left and right, don't believe that the frame is still bent. It isn't. The problem is most likely a spindle or strut that is bent.
Now, if the SAI readings are not the same, it is remotely possible that the vehicle is non-symmetrical as well. Verify this through your structural dimension guides. This will be a remote possibility for only a few vehicles, but just make sure before you jump to conclusions.
The following is a general guide to assist you in diagnosing the problem if SAI angles are not the same for left and right sides. There are some great training programs available to train you and your staff on this diagnostic method. I have taught many myself and others do the same. It is well worth your time and money to understand this diagnosis system since it is possible that your alignment guy doesn't.
In other words, if SAI is lower than specification, look for damage low. If SAI is greater than specification, look for damage high. Also, in both cases make sure to check that the lower ball joint is not bent. This left unchecked can misdirect many technicians into thinking damages exist in other areas.
To do this, raise the wheels off the ground and manually grab the tire and move each wheel through its turning radius. Pay attention to any abnormal (not smooth) rotation of the lower ball joint. This can be verified by removing the spindle from the ball joint and rotating the ball joint stud with vice grips. If it's not bent, the stud will rotate centered and not wobble.
Another consideration to look at is whether one side is less than specification and the other is greater than specification. For these cases, look first at the engine cradle or crossmember to ensure it is properly positioned. These opposite type readings usually indicate that it is not. Once this has been corrected, recheck the SAI angles.
Now, if there are no specifications for SAI given, then begin by assuming that the SAI reading provided for the undamaged (or least damaged) side is correct and use it as a guide for the other side. This can be misleading and caution must be used before jumping to conclusions. Once the correct reading has been verified, write it down for the next time.
Parts, parts, replace more parts
One real problem with this area during a collision repair is that there is a tendency to replace anything that might be damaged, rather than what really is causing the problem. This usually happens when only the camber reading is used to diagnose the problem and SAI or Included Angle (IA) is not used.Remember, improper camber angle readings are only a symptom of the real problem. It is very unfortunate the camber is what most alignment technicians fix at all costs even if it dramatically affects other alignment angles. One of the main truths I attempt to convey to any technician is, no one should ever sacrifice one alignment angle to fix another, and it must be properly diagnosed. Don't react to only the symptom, but fix the real problem.
As mentioned about SAI, one reason camber readings may be out of specification will be if the SAI angles are incorrect. This would be considered the real problem, not the symptom of the camber being incorrect.
Camber also will be out of specification if the IA is out of specification. IA is a calculated angle created by adding the SAI to the camber angle (Figure 3). This angle determines if there are bent or misadjusted parts between the upper and lower pivot points.
In other words, if the IA or camber is out of spec, then it's likely the strut and/or spindle is bent. If there is an adjustment for camber, check it first.
There are several documented procedures and even replacement bolt kits designed to fix camber problems. These should never be used to mask a problem with SAI or to mask a bent part, just as strut benders should never be used. Wheel alignment is the fine-tuning of the wheels for optimum driving. Proper diagnosis of the problem and proper structural repairs can make this easy. The special kits discount the importance of this and offer options, which are not recommended or safe.
Caster: The forgotten angle
Caster was used in the past as the primary directional control angle of the vehicle. Caster is defined as the forward or rearward tilt of the wheel's steering axis viewed from the side compared to true vertical (Figure 4). It is also normally measured in degrees and/or fractions of degrees. If a line was drawn down through the steering axis pivot points, the load of the vehicle in this example would be projected in front of the wheel's center. When the top steering pivot point is leaning back compared to the bottom steering pivot point, this is known as "positive caster." This causes a stable condition while driving forward and allows the vehicle to go straight ahead without wandering.Additional checks and measurements
There are other issues that need verification before any of the diagnosis steps for using SAI, caster, camber and IA should begin. The following are overlooked at times and cause many to reach incorrect conclusions about what is actually wrong. Many of the suspension problems related to alignment angles must be verified by test-driving the vehicle. When someone drives the vehicle they are experiencing clues (symptoms) of the condition. Whether the customer or the repairer does this, when these are not first checked, the diagnosis can lead into the wrong direction fast.
- Tire tread and size — Tread must match for at least left and right tires on the same axle of the vehicle or often the vehicle will pull due to the friction differences of each tire. If you want to verify this, switch the two tires in question side to side and see if the symptom reverses to the opposite direction. (vehicle pulled to right, now may pull to the left, etc.)
- Tire pressure —This always should be one of the first steps, and imbalanced tire pressure can cause vehicles to pull very noticeably.
- Ride height — If the vehicle leans to one side, it may often cause the vehicle to pull. Weak springs, bent springs, damaged mounting areas for springs, bent suspension parts and some damages to structure can affect the proper ride height of the vehicle. This can be verified when the vehicle's suspension is loaded and the bottom of the rocker panels are the same height from the frame rack or from a level floor. There are also several ride height specifications available for most vehicles that can be used in this verification. To verify which end of the vehicle is the cause, raise one end of the vehicle off the ground (centered) and watch to see if, once that end is unloaded, the difference between the left and right sides of the loaded end become equal. If it does, then the issue is not at that end of the vehicle. Just because the left front suspension area is low, that doesn't indicate that the damage is in the left front suspension.
- Brake pad pressure — Differences on one rotor compared to the other side may cause one to believe there are suspension problems, but it could really be the braking system. Verify that when the wheels are unloaded that the spinning effort and friction of the pads on each rotor are similar.
- Power steering pulls — A minor driving pull symptom can appear to be suspension, but may be the power steering system. Verify this by unloading the front wheels and starting the engine. If the steering wheel begins to rotate to one side, there is probably an imbalance in steering pressure.
Conclusion
A concept often overlooked is that the whole repair process of the structure is designed to restore the vehicle back to its pre-accident condition in regards to crash management, dimensions, durability and drivability. Why do we ignore, for the most part, the alignment specifications until we are done with everything, including the paintwork? Many times we ship the vehicle to the alignment guy with fingers crossed and a prayer said.
Everything we do structurally on the vehicle may affect whether or not the alignment will be successful. We must ensure that the control points affecting wheel alignment angles are properly measured and verified every time before it leaves the frame rack.
Use these solutions as your best friends, and suspension problems won't be a nightmare for your shop.
