See Figures 1 and 2
Caster is a measure of the angle between the steering axis and vertical, as viewed from the side of the vehicle when the wheels are in the straight ahead position. Stated another way, it is the tilting of the front steering axis either forward or backward from the vertical. A backward tilt is said to be positive (+) and a forward tilt is said to be negative (-).
Although is it measured using a special instrument, it can usually be seen by observing the location of the upper and lower control arm ball joints. A line drawn through the center of these 2 points represents the steering axis. When looking straight downward from the top of the upper control arm you can see if the ball joints are not aligned, indicating that the caster angle is more or less than 0 degrees. If vehicle has positive caster, the lower ball joint would be located ahead of the upper ball joint center line. If the vehicle has negative caster, the lower ball joint would be located behind the upper joint center line.
On 2wd trucks, the caster may be adjusted by changing placement of shims on the 2 upper control arm pivot shaft-to-frame bolts. On 4wd trucks, the caster is adjusted by turning the adjustment cams. To increase positive caster on a 4wd vehicle, move the front cam lobe inboard and the rear cam lobe outboard.
Camber is the measure of wheel tilt from the vertical direction, when the wheel is viewed from the rear of the vehicle. Camber is negative when the top of the wheel is inboard and positive when the top is outboard. Always check for bent, damaged or worn suspension components before determining that adjustment is necessary. The amount of tilt is measured in degrees from the vertical and this measurement is called the camber angle.
On 2wd vehicles, camber is adjusted by removing or adding shims at both front and rear pivot shaft-to-frame contact points. To increase camber, subtract shims equally from both locations. On 4wd vehicles, adjustment is once again made using the adjustment cams.
Toe is a measurement of how far a wheel is turned in or out from the straight ahead direction. When the front of the wheel is turned in, the toe is positive. When the front of the wheel is turned out, toe is negative. An incorrect toe setting can affect steering feel and cause excessive tire wear.
Stated another way, toe-in is the amount that the front of the wheels are closer together than the backs of the same wheels.
The actual amount of toe-in is normally only a fraction of a degree.
Toe adjustment is normally performed as the last of the wheel alignment settings (after caster and camber). It is adjusted by turning the tie rod adjustment sleeves in order to obtain the proper specification. After setting, the number of threads inside the adjuster sleeve must be equal, within a tolerance of 3 threads, on either end of the sleeve.
See Figures 3, 4 and 5
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), but for the MFI-Turbo the dimension should be 2.3-2.7 in. (3.6-69.6mm).