Your shop can address many potential alignment problems with careful inspection of key vehicle areas
Following a collision, vehicles often need to be aligned to fully return them to their pre-collision states. There are two possible causes for a vehicle being out of alignment: body/frame damage and damaged components. On occasion, a collision-repaired vehicle is sent to an alignment tech who finds that the vehicle cannot be adjusted back to alignment specifications. On those occasions, it's likely the vehicle will be sent back to the body shop – the thinking here being that the vehicle's structural components were not repaired properly. In reality, the vehicle probably has been repaired correctly; however, 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 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 need to be inspected for proper alignment and adjusted as needed.
There is a series of checks that should be performed while the vehicle is still in the collision repair shop before it is sent to the alignment department. These checks include such measurements as ball joint location, shock tower location and thrust line. Shops should check ride height and look for tie rod damage along with bent struts, steering knuckles and sector shafts. Finally, shops should test for wheel run out and "bump steer." If the vehicle is within tolerance structurally and the above checks and tests have performed (and the necessary parts replaced), the vehicle should align properly.Four significant measurements in relation to structural alignment must be returned to their proper location. Though some vehicles provide some adjustments for caster, camber, steering axis inclination (SAI) and toe, others may only provide adjustments for toe alignment. Note that camber is an inward or outward tilt of the tire at the top, compared to true vertical when the tire is viewed from the front of the vehicle.
Strut tower location
The strut tower location strongly influences a vehicle's alignment. 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 camber problems (on the damaged side), often indicate that another problem exists. If SAI is measured and found to be out of alignment, structural damage is likely. Note that the combination of SAI and camber is known as the included angle (see Fig. 1). If a camber problem is identified on any suspension type (McPherson, Short/long arm [SLA] or solid axle), the cause of the camber misalignment should be identified. The technician should re-check mounting locations and inspect the vehicle for bent components.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 of a vehicle with no damage is 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 (see Fig. 2). Vehicles with caster problems are likely to have a pull steer problem.Thrust line
Two terms are used to describe tracking alignment. The first is thrust line, the line perpendicular to the rear wheels. This is the direction the rear wheels go in relation to the vehicle centerline. The second term is thrust angle, the angle between the thrust line and the vehicle's centerline. If both the thrust line and thrust angle align, the angle is set at zero. When the thrust line projects to the right of the vehicle's centerline, the angle is a right thrust angle. If it projects to the left of the centerline, the angle is a left thrust angle.
Both of these angles indicate the vehicle is out of alignment, causing it to pull to the side opposite of the direction of the thrust line. A misaligned thrust line causes the steering wheel to be misaligned when the vehicle is moving straight.
Engine cradle misalignment
Engine cradle, K-member, sub frame: Called different names by different manufacturers, this structure holds the engine and often such steering components as the rack and pinion. It too must be checked to ensure 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 previously discussed 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 (see Fig. 3) should be performed off the machine after the engine cradle alignment is confirmed.Ride height
This measurement is 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. Performing a thorough inspection of a vehicle's ride height can indicate worn or bent suspension components.
Tie rod damage
Following the ride height inspection, put the vehicle on a level surface, and inspect for tie rod damage and steering arm damage. If both of the vehicle's front wheels face the same direction when the steering wheel set in the locked straight-ahead position, the steering system is most likely not damaged.
If, however, one of the wheels faces forward and the other turns in or turns out, a steering arm and/or a tie rod likely is damaged.
Bent strut
See Fig. 4. Identify a bent strut by loosening the strut shaft upper lock nut and rotating the shaft 360 degrees 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. Caution: When the test is completed, retighten the locking nuts.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, recycled suspension parts cannot be used. Always check your area for restrictions.
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. During a collision, severe direct impact to front wheels can twist the sector shaft. 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). Always perform a close and careful inspection.
Conclusion
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. Go to www.icar.com for more information.
