CASTER, CAMBER, AND TOE-IN
See Figures 1 through 5
Caster is the angle at which the front steering axis tilts either forward or backward from a vertical position. Positive caster is a backward tilt while a forward tilt is negative caster. Caster angle on the Camaro suspension cannot be seen with the eye, it requires the use of instruments. Caster angle can, however, be visualized. If you look down from the top of the upper control arm to the ground, you notice that the upper and lower ball joints do not line up (unless a 0 degree caster angle existed). With any angle (other than 0 degrees), one ball joint would be slightly ahead or slightly to the rear of the other. If you had a positive angle, the lower ball joint would be slightly ahead (more to the front of the car) of the upper ball joint.
The front wheels will tilt outward or inward at the top depending on whether the camber is positive or negative. Camber angle then is the amount (in degrees) that a wheel tilts from a perfectly vertical position. When the wheels tilt outward at the top, it has positive camber; camber is negative when the wheel tilts inward at the top.
Toe-in, measured in fractions of an inch, is the turning in of the front of the front wheels. The front wheels must roll parallel to each other; if they don't, uneven tire wear will result.
When performing a front wheel alignment, the mechanic checks all three of these measurements and makes any necessary adjustments. Since one adjustment affects each of the others, they must be adjusted in a specific order: caster, camber, and then toe-in. Proper wheel alignment is necessary for ease and stability of steering and controlling tire wear.
Adjustment of caster and camber is carried out by adding or subtracting shims between the upper control arm shaft and the frame bracket. Camber is adjusted by adding or subtracting shims from both the front and rear of the shaft. Adding shims decreases positive camber. Caster is adjusted by adding or subtracting shims from one end of the shaft. Moving one shim to the front bolt from the rear bolt will decrease positive caster. To adjust, loosen the shaft-to-frame nuts and add or subtract shims as necessary. Tighten the nuts to 55 ft. lbs. when the adjustment is final. At least two bolt threads should be protruding from the shim pack. The difference between the front and rear shim pack should never exceed 2 / 5 in.
Toe-in is adjusted after the caster and camber adjustments are carried out. Adjust the toe-in by loosening the clamps on the tie-rod sleeves, and turning the sleeves an equal amount in the opposite direction, to maintain wheel spoke alignment while adjusting.