GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Wheel Alignment


If the tires are worn unevenly, if the vehicle is not stable on the highway or if the handling seems uneven in spirited driving, the wheel alignment should be checked. If an alignment problem is suspected, first check for improper tire inflation and other possible causes. These can be worn suspension or steering components, accident damage or even unmatched tires. If any worn or damaged components are found, they must be replaced before the wheels can be properly aligned. Wheel alignment requires very expensive equipment and involves minute adjustments which must be accurate; it should only be performed by a trained technician. Take your vehicle to a properly equipped shop. Following is a description of the alignment angles which are adjustable on most vehicles and how they affect vehicle handling. Although these angles can apply to both the front and rear wheels, usually only the front suspension is adjustable.


See Figure 1

Looking at a vehicle from the side, caster angle describes the steering axis rather than a wheel angle. The steering knuckle is attached to a control arm or strut at the top and a control arm at the bottom. The wheel pivots around the line between these points to steer the vehicle. When the upper point is tilted back, this is described as positive caster. Having a positive caster tends to make the wheels self-centering, increasing directional stability. Excessive positive caster makes the wheels hard to steer, while an uneven caster will cause a pull to one side. Overloading the vehicle or sagging rear springs will affect caster, as will raising the rear of the vehicle. If the rear of the vehicle is lower than normal, the caster becomes more positive.

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Fig. Fig. 1: Caster affects straight-line stability. Caster wheels used on shopping carts, for example, employ positive caster


See Figure 2

Looking from the front of the vehicle, camber is the inward or outward tilt of the top of wheels. When the tops of the wheels are tilted in, this is negative camber; if they are tilted out, it is positive. In a turn, a slight amount of negative camber helps maximize contact of the tire with the road. However, too much negative camber compromises straight-line stability, increases bump steer and torque steer.

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Fig. Fig. 2: Camber influences tire contact with the road


See Figure 3

Looking down at the wheels from above the vehicle, toe angle is the distance between the front of the wheels, relative to the distance between the back of the wheels. If the wheels are closer at the front, they are said to be toed-in or to have negative toe. A small amount of negative toe enhances directional stability and provides a smoother ride on the highway.

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Fig. Fig. 3: With toe-in, the distance between the wheels is closer at the front than at the rear

TRIM HEIGHT ("Z"Measurment)

See Figures 4, 5 AND 6

The trim height "Z" measurement is used as an indicator if the front suspension is properly set-up. The height may be checked following suspension repairs or if damage to the suspension is suspected, such as after hitting a large pot hole. Refer to the illustrations for proper measurements. On 2WD vehicles, if the measurement is out of specification, check for worn or damaged suspension components. On 4WD vehicles, some adjustment is possible through the torsion bar adjuster. Turning the adjustment bolt one full revolution will increase/decrease "Z" height by 0.2 in. (6.0mm). If a proper adjustment cannot be obtained, check for worn or damaged components. The proper specification for most 4WD models is 4.6-5.0 in. (116-128mm)

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Fig. Fig. 4: Measuring the trim height "Z" dimension-2WD vehicles

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Fig. Fig. 5: Measuring the trim height "Z" dimension-4WD vehicles

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Fig. Fig. 6: Adjusting the trim height on 4WD vehicles