If the tires are worn unevenly, if the vehicle is not stable on the highway or if the handling seems uneven in spirited driving, the wheel alignment should be checked. If an alignment problem is suspected, first check for improper tire inflation and other possible causes. These can be worn suspension or steering components, accident damage or even mismatched tires. If any worn or damaged components are found, they must be replaced before the wheels can be properly aligned. Wheel alignment requires very expensive equipment and involves minute adjustments that must be accurate; and should only be performed by a trained technician. Take your vehicle to a properly equipped shop.
The alignment angles that apply to the front wheels also apply to the rear wheels. The following is a description of the alignment angles, which are adjustable on A4 and Passat vehicles and how they affect vehicle handling.
On 1990-97 Passat front wheel drive models, the front camber and toe are adjustable. Because the rear axle is essentially a beam, the toe can be equalized but not adjusted individually for each wheel.
On A4 and 1998-00 Passat front wheel drive models, the front camber can be equalized and toe-in adjusted with the vehicle unladen and raised. As with earlier models, the toe can be equalized but not adjusted individually for each wheel.
On A4 and 1998-00 Passat All Wheel Drive (AWD) models, the front camber can be equalized and toe adjusted with the vehicle unladen and raised. The rear toe and camber can be adjusted individually for each wheel.
On all A4 and 1999-00 Passat models the front toe must also be checked at normal ride height as well as at a specific raised vehicle height depending on the installed suspension version. Obtaining the proper toe in on these models may require that the tie rod end (track rod) be moved up or down in the bearing housing (knuckle) to achieve the correct ride height toe.
Note that the front caster cannot be adjusted on either the A4 or the Passat models. During an alignment, if a caster related problem is discovered, the front subframe can be moved slightly in an attempt to equalize the caster, however if the caster is beyond an acceptable range, the vehicle should be inspected for damaged or worn components.
Looking at a vehicle from the side, caster angle describes the steering axis rather than a wheel angle. The steering knuckle is attached to a strut at the top and a control arm at the bottom. The wheel pivots around the line between these points to steer the vehicle. When the upper point is tilted back, this is described as positive caster. Having a positive caster tends to make the wheels self-centering, increasing directional stability. Excessive positive caster makes the wheels more difficult to steer, while an uneven caster will cause a pull to one side. Overloading the vehicle or sagging rear springs will affect caster, as will raising the rear of the vehicle. If the rear of the vehicle is lower than normal, the caster becomes more positive, conversely as the rear is raised, the camber is reduced.
If the front caster varies from side to side, the lower subframe fasteners can be loosened and the subframe moved slightly around the bolt holes for minute adjustments.
Suspension tuning is a key element in improving the cornering ability of a vehicle, and should only be performed by a knowledgeable and experienced technician.
Looking from the front of the vehicle, camber is the inward or outward tilt of the top of wheels. When the tops of the wheels are tilted in, this is negative camber; if they are tilted out, it is positive. In a turn, a slight amount of negative camber helps maximize contact of the tire with the road. However, too much negative camber compromises straight-line stability, increases rolling resistance, bump steer and tighten steer.
Although not adjustable from the factory, adjustable front camber plates are available from aftermarket suppliers. Suspension tuning is a key element in improving the cornering ability of a vehicle, and should only be performed by a knowledgeable and experienced technician.
On All Wheel Drive (AWD) models, the rear camber is adjusted by loosening the locknut of a through bolt, and moving an eccentric washer that is keyed to the bolt.
Looking down at the wheels from above the vehicle, toe angle is the distance between the front of the wheels, relative to the distance between the back of the wheels. If the wheels are closer at the front than at the rear, they are said to be toed-in or to have negative toe. A small amount of negative toe in the front end enhances directional stability and provides a smoother ride on the highway, however too much toe in will cause the front of the car to dart, or turn in quickly on a turn. A slight toe out may improve the ultimate turn-in ability of the vehicle, however too much toe out may cause the mid corner performance to be compromised and create excessive under-steer.
The rear toe should typically be set for toe in. Toe-out should only be approached by a professional suspension expert for extreme cases where extensive modifications have been performed and the use of specific components require ignoring factory specifications.
The front toe is adjusted by loosening a locknut and then rotating a threaded steering arm. On 1990-97 Passat models, the left side tie rod length is set to a specified distance and the total toe is set and adjusted with the right tie rod.
On A4 and 1998-00 Passat models, both tie rods are adjusted to center the steering wheel and to set the individual toe for each front wheel.
The rear toe on A4 and 1998-00 Passat All Wheel Drive (AWD) models is adjusted by moving an eccentric washer on one of the trailing arms where it attaches to the subframe.