374 Auto Suspension and Steering Copyright by Goodheart-Willcox Co., Inc. Th ese bolts are made with a small central shank or a fl at side. Th e bolt is installed in place of one of the original equip- ment strut bolts. Th is allows the strut to be moved for cam- ber adjustments. On some vehicles, camber and caster are not adjustable. Replacement of damaged parts is necessary to achieve proper alignment. Rear Toe An important reason to set the rear toe is to maintain the best rear-wheel tracking. Proper tracking is obtained when the rear wheels follow directly behind the front wheels when the vehicle is moving in a straight line. Perfect tracking is obtained when the vehicle’s thrust line is directly on top of the vehicle’s geometric centerline, Figure 17-26. Th is is not always possible, but the two should match as closely as pos- sible. Th erefore, the total rear toe should not only be cor- rect, but it should be evenly divided between sides. If this is not done, the vehicle will travel down the road at an angle (called dog tracking) and the steering wheel will be diffi cult to center. Rear toe can be set using eccentric cams, slotted holes, or threaded rods. When cams are used, the adjustment pro- cedure is the same as that for camber, Figure 17-27. On a few vehicles, toe is adjusted using slotted holes where the front of the control arm contacts the frame. To adjust toe using a slotted hole, loosen the nut and bolt. Th en push or pull the suspension part or tire until toe is correct. Finally, tighten the nut and bolt while holding the suspension part in position. If the vehicle is equipped with threaded rods for toe adjustment, loosen the locknuts and turn both nuts in the same direction until the toe is correct. On most vehicles using this system, the adjusting rod is a strut or stabi- lizing rod extending ahead of the rear axle, as shown in Figure 17-28. On a few rear suspensions, the rod extends from the center of the vehicle to the lower control arm. If the vehicle has a four-wheel steering system, the tech- nician may need a special tool to lock the rear steering gear. Th e rear steering gear must be locked before setting the rear camber and toe. Th e tool is removed to set the front caster and camber and then reinstalled during front toe adjust- ment. See Figure 17-29. Not all four-wheel steering systems require this tool. Setting Rear Wheel Alignment with Shims Many late-model front-wheel drive vehicles have no camber or toe adjusting devices. To adjust the rear axles on some of these vehicles, metal or plastic discs called full-contact shims are used. Shims in the form of fl at metal strips are also available. Rear axle shims were discussed in Chapter 16. Shims are thicker on one side than the other side, as shown in Figure 17-30. Shims can also be used on some vehicles when the factory adjustment at the rear axle is used up. Th e amount of caster and toe change required is determined by comparing the manufacturer’s specifi cations to the actual alignment readings. Th e needed shim thickness and place- ment can then be calculated. To install a shim, determine the shim’s thickness and its placement. Th en, remove the rear brake drum or rotor. Strut Special camber- adjusting bolt assembly Sleeve Goodheart-Willcox Publisher Figure 17-25. Adjusting camber with special bolts. These bolts are normally used on vehicles that do not have provisions for adjustment. Thrust line is directly above the geometric centerline Hunter Figure 17-26. Rear toe has been set to factory specifications. The vehicle’s thrust line perfectly matches the geometric centerline. The thrust angle is reduced to zero.