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Re-aligning vehicle alignment education

Tuesday, January 6, 2015 - 09:00
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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


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