370 Auto Suspension and Steering Copyright by Goodheart-Willcox Co., Inc. Installing the Alignment Head Th e alignment head consists of the electronic or light assem- bly and the head frame assembly. Th e electronic assembly is free to turn in relation to the head frame assembly, which is attached to the rim. A lock is used to tighten the elec- tronic assembly to the wheel or frame when necessary. See Figure 17-17. Most alignment heads are attached by clamp- ing them to the inside of the rim. Many modern wheel rims are made of aluminum, magnesium, or chromed steel, and could be scratched by the clamping device. On these rims, special adaptors are used to clamp the head to the outside of the rim. Aft er the head is clamped to the rim, safety straps are attached to the rim to keep the head from falling on the fl oor and being damaged if the clamps slip. On a few machines, alignment wires, called strings, must be installed between the front and rear heads. Compensating the Alignment Head All rims have some runout, and therefore, there is no way to install the alignment head without slight misalignment between the rim and head. Th is runout must be removed to prevent incorrect readings. Th e procedure to remove run- out may vary from one equipment manufacturer to another. With most types of equipment, the procedure is to spin the wheel and rim 1/2 turn (180°) with the head attached. Th en, use the runout compensation device on the alignment equipment to compensate for any runout. Turn the wheel 1/2 turn again and repeat the procedure. Most computerized alignment machines use lights on the head or readouts on the screen to tell you when the head is properly compensated. Repeat the procedure for all wheels. When all four wheels are compensated, the screen will give a set of alignment readings. Since the wheels are off the ground, disregard the readings at this time. Caution: Never allow the rim and head assembly to turn after it has been compensated. Any movement from the vertical (straight up and down) position will affect readings. Lowering the Vehicle Before lowering the vehicle, make sure the turning plates are centered under the wheels and remove the turntable lock- ing pins. Apply the parking brake fi rmly and then lower the vehicle. When the vehicle is resting on the turning plates, bounce it at the front and rear bumpers. Th is takes any ten- sion out of the suspension parts and allows the vehicle to settle to its normal resting position. See Figure 17-18. Centering the Steering Wheel If the vehicle has power steering, start the engine and allow it to idle. Turn the steering wheel from side to side several times to equalize play in the steering linkage. Th en, center the steering wheel. Turn the engine off if necessary. It is not necessary to install the wheel holding tool. However, you will need this tool later during the alignment procedure. See Figure 17-19. Wheel cover lock Wheel cover key Wheel cover lock Aluminum wheel Locknut Locknut key Lug wrench Nut socket Nut caps Lug nut Hubcap General Motors Figure 17-15. One particular wheel cover (hubcap) lock being removed with a special lock key. General Motors Figure 17-16. This aluminum wheel uses a special locknut. A nut removal key is needed to remove the wheel. ThamKC/Shutterstock.com Figure 17-17. A lock is used to secure the alignment head to the wheel.