Re-aligning vehicle alignment education

Jan. 6, 2015
Technicians can restore damaged steering systems with diligence, knowledge and training.

Caster, camber, toe-in/toe-out, toe-out on turn, steering axis inclination, included angle, thrust angle — the list could go on. All of these angles and measurements must be returned to their vehicle-specific settings after a repair so that the car will steer correctly, have proper tire wear and be safe to operate. The task can seem daunting. Yes, there are technicians that only do alignments, both following collisions and for normal vehicle and tire wear. So as collision technicians, what should we know?  This article is not intended to teach you all there is to know about steering and suspension components, alignment, procedures and/or damage analysis. What it is intended to do is either refresh your memory or highlight the important areas that you should know concerning a vehicle’s alignment following a collision.  First let’s start with some suspension types.

MacPherson suspension system
Though there are many different types of front-end suspensions, the MacPherson is by far the most common.  It is used commonly on front-wheel drive vehicles and on all-wheel vehicles of monocoque design. The position of the upper mount is critical to the vehicle’s steering angles, especially the steering axis inclination (SAI). The strut assembly, which is also the shock absorber, if bent, will greatly alter the spindle’s position. A test for a bent strut assembly will be discussed later.

The location of the spring on a MacPherson suspension is normally high on the strut, as in Fig. 1, but may be located lower between the control arm and the vehicle’s body, as in Fig. 2.

Short, long arm suspension
Short and long arm suspension (SLA) (Fig 3) is also a frequently used type of suspension, commonly found in vehicles with rear wheel drive. In the illustration, the lower long arm cradles the lower spring and the upper short control arm cradles the upper part of the spring, with the shock absorber running in the center.

I-beam suspensions
I-beam suspensions, either single or twin, as in the illustration (Fig. 4), were once found on light duty trucks and have now been replaced with SLA on most pickups. They can be found on heavy trucks, however, because of their ability to suspend higher weights of the bigger vehicles. 

Next let's look at steering terms and angles.

Figure 1 Figure 2 Figure 3 Figure 4

Camber
Camber (Fig. 5) is the inward or outward tilt of the top center of the wheel when viewed from the front of the vehicle. It is commonly identified as either negative camber (inward), positive camber (outward), or zero camber. The camber angle is measured in degrees from true vertical or zero camber.

Camber is a wear angle, and if the angle is incorrect, either the inside or the outside of the tire contacts the surface exclusively. This places the entire weight of the vehicle on a small part of the tire, thus wearing it down more than the remainder of the tire. An incorrect positive camber will wear the tire more on the outside, while an incorrect negative camber setting will wear the inside of the tire more. Keep in mind that vehicles may have a proper camber setting that may be either positive or negative which is correct for that vehicle and will not wear the tire incorrectly. It is only when the camber setting is more (either positive or negative) than specified that results in abnormal tire wear.

The vehicle’s tires should be inspected for such incorrect tire wear, which may indicate that the vehicle was not in proper alignment prior to the collision.  

Caster
Caster is described as the forward or rearward tilt of the front wheel on the steering axis, when viewed from the side, which is straight line from the upper pivot point, strut or upper ball joint, through the lower pivot point, the lower ball joint.  Camber is also referred to as either positive (rearward of the steering axis) or negative, which would be forward of the steering axis (Fig. 6). Again remember that a setting for a vehicle may be either positive or negative and still be correct. It is only when the setting is outside these prescribed settings that steering troubles result.

Toe in/toe out
Toe is the dimensional difference between the front of the front wheel and the rear of the front wheel (Fig. 7). Toe is the single most critical angle that is set during an alignment, and it is always set last after all other measurements have been taken and adjusted. It is a wear angle, and if incorrect, it can cause excessive tire wear in a very short time. It is also described as positive (toe-in) or negative (toe-out). Incorrect positive or negative toe can cause tire scrubbing, and / or feathering.  

Toe-out on turn (Fig 8) is a non-adjustable angle that is affected by the steering arm only. It can be corrected by replacing one or both of the steering arms that may have been bent during a collision. This is also a tire wear angle, but it affects the vehicle most significantly during a turn. Each wheel takes a slightly different path on a turn that is affected by the steering arms on the vehicle. Turn angle out of specifications will have a poor response on a turn, squealing tires, and/or excessive front tire wear.

Figure 5 Figure 6 Figure 7 Figure 8

Steering axis inclination
SAI (Fig. 9) is the degree or amount of inward tilt of the upper pivot point from a true vertical line on the steering assembly. This inward tilt tends to keep the wheel pointed straight ahead. It is also largely responsible for returning the wheel to a straight-forward position after a turn is completed. In older service manuals, it may be referred to a King pin inclination (KPI), but if used correctly, SAI is only correct on I-beam suspension. Possible causes for out-of-spec SAI include: tip pivot point moved in or out, bottom pivot point in or out, or unibody structure out of specs. SAI plus actual camber (positive) or minus actual camber (negative) is the included angle. When camber is positive, add it to the SAI angle. If camber is negative, subtract it from the SAI angle. This angle is used as a diagnostic tool to determine if structural misalignment is present or suspension parts are bent.

Thrust angle
The thrust angle (Fig. 10) is the direction all four wheels move in relation to the vehicle’s centering. It is determined by the position of the rear axle and the toe of the wheels. If the rear wheels are aimed straight forward and are parallel to the centerline, the vehicle will move straight forward. This is referred as a zero-thrust angle or no-thrust angle, which is the ideal effect. On the other hand, if one of the wheels is toed-out and the other is toed-in, the rear of the vehicle will tend to run out toward the side with the toed-out wheel. This is commonly referred to as dog tracking. An out-of-specs thrust angle will dog-track, have unbalanced steering on turns, oversteering or understeering, and/or fast tire wear. 

Bump steer
Bump steer (Fig. 11) is not considered one of the alignment geometry angles or one of the alignments usually made as part of a wheel alignment, but it is a condition that can become an issue after a frontal collision. Bump steer describes a condition in which, after a vehicle hits a bump, it wants go in one direction and then another, or it darts and dives, without moving the steering wheel. Bump steer is caused when the rack and pinion steering system is misaligned. The rack is usually the cause of the bump steering. A variance of as little as 3mm (1/8 in) can cause the vehicle to bump steer. Normally the causes of bump steering in rack and pinion steering vehicles are misaligned rack and pinion, improperly repaired strut tower, misaligned engine cradle, or misaligned lower control arm mounting locations.

Bump steer can also be experienced on vehicles that have a standard gearbox/steering box and idler arm. With this diagnosis, the cause for the bump steer response is the intermediate tie rod not being parallel with the vehicle.

Following a collision, a vehicle will often need to be aligned to completely to return the vehicle to its pre-collision state. There are two possibilities that could cause a vehicle to be out of alignment: body/frame damage or damaged components. On occasions a collision-repaired vehicle is sent to the alignment tech who finds that the vehicle cannot be adjusted back to alignment specifications. It is likely that the vehicle will then be sent back to the body shop, the thinking being that the vehicle’s structural components were not repaired properly. In reality, the vehicle has probably been repaired correctly, but there still may be steering components that have been bent and are in need of replacement.  If collision repair technicians are to be certain that the repairs they perform are complete, they will need to check not only the structural frame/body alignment, but also components of the suspension, engine cradle or sub frame, and steering gear. Vehicles that have sustained collision damage to steering or suspension mounting locations, damage to suspension parts, engine cradle damage or misalignment, or damage in a rollover, will need to be inspected for proper alignment and adjusted as needed. This is why it is imperative to measure the vehicle three dimensionally.

There is a series of checks that should be performed while the vehicle is still in the collision repair shop, prior to sending it to the alignment department. The checks include such measurements as ball joint location, shock tower location, and thrust line. Also, such inspections as ride height and checks for tie rod damage, bent strut, bent steering knuckle, bent sector shaft; and tests for wheel run out and “bump steer”, should be completed. If the vehicle is within tolerance structurally and the above checks and tests have performed (thus necessary parts have been replaced), it is likely that the vehicle will align properly when sent to the alignment technician.

Figure 9 Figure 10 Figure 11

Strut tower location
The strut tower location strongly influences a vehicle’s alignment, and though some vehicles provide adjustment for camber using slotted holes in the top of the strut tower, these adjustments are limited. The proper location of the strut tower should be verified while structural analysis and repairs are being performed. Camber problems, especially one-sided (on the damaged side) camber problems, often indicate that another problem exists, one possibility being a bent strut. If Steering Axis Inclination is measured and found to be out of alignment, structural damage is likely. If a camber problem is identified on any suspension type (McPherson, Short/long arm or solid axle), the cause of the camber misalignment should be identified. The technician should recheck mounting locations, and should also perform an inspection for bent components.

Bent strut
A bent strut (Fig 12) can be identified by loosening the strut shaft upper lock nut and rotating the shaft 3600 with a wrench. While rotating the shaft, and using the fender lip as a reference, look for a change in the tire tilt. Movement indicates a bent shaft. (REMINDER: When the test is completed, retighten the locking nuts.)

Ball joint location
Most structural measuring devices provide specifications and are capable of measuring the location of the lower ball joint. If these measurements are not available, the technician could take a comparative measurement from right to left. If there is damage on both sides of the vehicle, taking a comparative measurement to a non-damaged vehicle is also an option. If, after structural alignment is completed, the technician finds the lower ball joint to be misaligned, further inspection must be performed.

The lower ball joint, when moved toward the front or rearward of the vehicle, affects caster — the tilt of the steering axis toward the front or rear of a vehicle compared to true vertical. Vehicles with caster problems are likely to have a pull steer problem.

Engine cradle misalignment
Engine cradle, K-member, sub frame — it may be called different names by different manufacturers, but the structure that holds the engine and often the steering components such as the rack and pinion in the vehicle must also be checked for proper alignment. If the rack and pinion is misaligned, bump steer may occur. Bump steer is a change in tow as the vehicle’s suspension moves up and down while in motion. Bump steer can cause a vehicle to pull, even when the steering wheel is in the straight-ahead direction. If the rack and pinion is not mounted on the engine cradle, its proper alignment should be checked. 

All of the above measurement and alignments checks should be performed prior to removing the vehicle from a structural alignment machine. Strut tower measurements, lower ball joint, thrust line and engine cradle alignment all are performed on the frame machine. The test for bump steer should be performed after the engine cradle alignment is confirmed, off the machine (Fig. 13).

Figure 12 Figure 13

Ride height
This measuremet will give a good indicator of worn or damaged parts. The vehicle is placed on a level surface with the suspension loaded (the weight of the vehicle on the suspension). No abnormal weight should be in the vehicle’s passenger compartment or trunk, as this may cause a misalignment. Measurements are taken from side-to-side, measuring from symmetrical locations to determine if the vehicle is level. Inspect for sagging suspension, unevenly worn tires, and dipping in the front or rear. Check for worn or sagging struts when side-to-side measurements are compared. A thorough inspection of a vehicle’s ride height can indicate worn or bent suspension components.

Tie rod damage
With the vehicle on a level surface, following the ride high inspection, a vehicle should be inspected for tie rod/steering arm damage. If, when the steering wheel is in the locked straight-ahead position, both wheels are facing the same direction, then it is likely that the steering is not damaged. If, however, one wheel is facing forward and the other is turning in or out, it is likely that a steering arm and/or a tie rod is damaged.

Bent steering knuckle or spindle
To check for a bent steering knuckle or spindle, place a straightedge vertically on the rotor. Measure from the straightedge to various points on the strut, and then compare those measurements to a non-damaged side for comparison. Damaged parts must be replaced. In some states, used (LKQ) suspension parts cannot be used; check in your area for restrictions. Contrary to some misinformation, knuckles do bend and can deform greatly prior to fracturing.

Bent sector shaft
Evaluation of suspension parts on a damaged vehicle is not complete until the technician has inspected the sector shaft for wear or damage. This will generally be on vehicles with a steering box, parallelogram steering system. During a collision, severe direct impact to front wheels can twist the sector shaft, and in severe cases the shaft can be completely broken. (Though a broken sector shaft is rare, it is more easily identified than a twisted one.) Close and careful inspection should therefore be performed.

Conclusion
Steering and suspension assessment, diagnoses, and repair can be complex, primarily due the number of components involved.  The consequence of incomplete operations in any of these areas, though, is a steering system that does not function as it should after repair. With a good knowledge of the different types of steering systems on vehicles, along with a close and careful inspection of their components, the diligent technician can restore damaged vehicles to their pre-accident conditions during the repair process. For further training in collision repair steering and suspension, I-CAR offers a series of face-to-face classes; if interested, log into to www.icar.com for more information.

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