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 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 most Chevrolet mid-sized vehicles, the caster may be adjusted by changing placement of shims on the 2 upper control arm pivot shaft-to-frame bolts.
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.
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 fronts of the wheels are closer together than the backs of the same wheels. Some vehicles are set with a slight tow-out (backs of the wheels are closer together than the fronts) in order to prevent excessive toe-in under power.
The actual amount of toe-in is normally only a fraction of a degree. The purpose of toe-in is to ensure parallel rolling of the front wheels. (Excessive toe-in or toe-out will cause tire wear).
Caster and camber can be adjusted by moving the position of the upper control arm assembly using shims between the pivot shaft and the frame. Tilting the assembly forward/rearward (by transferring shims from front-to-rear or rear-to-front) adjusts caster. Movement it inboard/outboard (adding or subtracting shims to both ends of the pivot shaft) adjusts camber.
- Loosen the clamp bolts at each end of the steering tie rod adjustable sleeves.
- With the steering wheel set straight ahead, turn the adjusting sleeves to obtain the proper adjustment.
- When the adjustment has been completed, check to see that the number the threads showing on each end of the sleeve are equal. Also check that tie rod end housings are at the right angles to the steering arm.