372 Auto Suspension and Steering Copyright by Goodheart-Willcox Co., Inc. Checking Steering Axis Inclination Steering axis inclination (SAI) is usually checked as part of the caster checking process. SAI should be checked when- ever there is evidence of collision damage or the vehicle has a handling or tire wear problem that cannot be accounted for by another cause. Th e brakes should be locked for the SAI check. Some equipment manufacturers specify that the heads be free to pivot on the head frame when both caster and SAI are checked in one operation. Checking Toe-Out on Turns Toe-out on turns is seldom incorrect, but it should be checked whenever you suspect steering arm damage or when the tires squeal excessively on turns. To check toe-out on turns, the brake pedal depressor should be in place. To make this check, turn one of the front wheels inward until the turntable indicator reads 20°. Aft er this is done, move to the other side of the vehicle and read the indicator on that turntable. Th e reading should be slightly more than 20°. See Figure 17-22. Record this reading then turn the wheel inward to the 20° indicator on the turntable. Read the indicator on the other turntable. Th is reading should also be slightly more than 20°. Compare the readings with speci- fi cations. If the readings are incorrect, the steering arms should be replaced. To determine which steering arm is bent, measure the distance between the end of one steering arm at the tie rod and the side of the tire. Th is can be done by inserting your hand between the tie rod and the tire sidewall. Repeat the procedure on the other side of the vehicle. Th e measurement should be the same on both sides of the vehicle. A slight varia- tion (less than one inch or 2.54 mm) is acceptable, but larger variation indicates that one of the steering arms is bent and should be replaced. Check for impact damage to the steering arms to determine which one should be replaced. Adjusting Toe with Trammel Bars When a vehicle needs only toe adjustment, some shops adjust the toe using a trammel bar. To use a trammel bar, raise both wheels off the ground and scribe a mark completely around the tire. Hold a punch or other pointed tool against the outside of each tire tread as another technician spins the tire. Th en place the vehicle on the ground and drive it back and forth a few times to settle the suspension. Use the tram- mel bar to measure the distance between the scribed lines at the front of the tire. Th en measure the distance between the lines at the rear of the tires. Th is measurement can also be done with a steel tape if you have an assistant to hold one end of the tape. No matter what type of measurement device is used, the measuring point should be at the same height at the front and rear of the tire. Th e diff erence in the front and rear distances is the toe. If the measurement is greater at the rear, the vehicle is toed in. If the measurement is greater at the front, the vehicle is toed out. Th e trammel bar method gives an acceptable toe measurement, but it cannot be used to center the steering wheel. Th e importance of centering the steering wheel was discussed in Chapter 16, Wheel Alignment Principles. Adjusting Alignment Once the actual vehicle alignment has been established, you must determine whether the vehicle requires adjustment, and what adjustment must be made. Note: If your alignment machine has a printer, you may want to make a printout of the current alignment to aid in adjustment. Rarely is a vehicle in perfect adjustment. Th e toe is almost always incorrect, even when other readings are within specifi cations. Before adjusting the vehicle, you must Alignment rack Turning plate Ford Figure 17-21. Move the front tire and wheel to the left and right to check the caster. Front 20° 23.5° Turning plate Ammco Figure 17-22. Checking toe-out on turns. Follow the vehicle manufacturer’s testing procedures.