See Figures 1, 2, 3, 4 and 5
Correct alignment of the front suspension is necessary to provide optimum tire life and for proper and safe handling of the vehicle. Caster and camber cannot be set or measured accurately without professional equipment. Toe-in can be adjusted with some degree of success without any special equipment.
Caster is the tilt of the front steering axis either forward or backward away from the vertical. A tilt toward the rear is said to be positive and a forward tilt is negative. Caster is calculated with a special instrument but one can see the caster angle by looking straight down from the top of the upper control arm. You will see that the ball joints are not aligned if the caster angle is more or less than 0 degrees. If the vehicle has positive caster, the lower ball joint would be ahead of the upper ball joint center line. Caster is designed into the four wheel drive front suspension. Small caster adjustments can be made on four wheel drive front axles by the use of tapered shims between the springs and the axle.
Camber is the slope of the front wheels from the vertical when viewed from the front of the vehicle. When the wheels tilt outward at the top, the camber is positive. When the wheels tilt inward at the top, the camber is negative. The amount of positive and negative camber is measured in degrees from the vertical and the measurement is called camber angle. Camber is designed into the front axle of all four wheel drive vehicles. Small camber adjustments can be made on four wheel drive front axles by the use of an adjusting shim between the spindle and the steering knuckle. Any major corrections require axle straightening equipment.
CASTER AND CAMBER ADJUSTMENTS
Caster and camber adjustments are made by removing or adding shims between the upper control arm shaft and the mounting bracket which is attached to the suspension crossmember.
Front wheel alignment on Chevrolet and GMC trucks is a complex operation. Specifications for camber and caster are given in relation to a measurement (the distance from the lower control arm to the bump stop bracket). This takes into account all sorts of individuality among trucks: heavy duty suspensions, tires, spring rates, and even wear on the front suspension. As a result specifications are not included in this information. Camber should not vary more than 1 /2º from side to side.
See Figure 6
Toe-in is the amount, measured in a fraction of an inch, that the wheels are closer together in front than at the rear.
Virtually all trucks are set with toe-in. Some four wheel drive trucks require toe-out to prevent excessive toe-in under power.
Some alignment specialists set toe-in to the lower specified limit on vehicles with radial tires. The reason is that radial tires have less drag, and therefore a lesser tendency to toe-out at speed. By the same reasoning, off-road tires would require the upper limit of toe-in.
Toe-in must be checked after caster and camber have been adjusted, but it can be adjusted without disturbing the other two settings. You can make this adjustment without special equipment, if you make careful measurements. The adjustment is made at the tie rod sleeves. The steering must be set so the wheels are pointing straight ahead.
- Toe-in can be determined by measuring the distance between the centers of the tire treads, front and rear. If the tread pattern of your tires makes this impossible, you can measure between the edges of the wheel rims, but make sure to move the truck forward and measure in a couple of places to avoid errors caused by bent rims or wheel runout.
- Loosen the clamp bolts on the tie rod sleeves.
- Rotate the sleeves equally (in opposite directions) to obtain the correct measurement. If the sleeves are not adjusted equally, the steering wheel will be crooked when the wheels are pointed straight ahead.
If your steering wheel is already crooked, it can be straightened by turning the sleeves equally in the same direction.
- When the adjustment is complete, tighten the clamps.
See Figure 7