A vehicle has a shimmy when the steering wheel returns to center after completing a turn. Which of the following could be the cause?

When analyzing the situation where a vehicle experiences a shimmy in the steering wheel as it returns to center after a turn, excessive positive caster can indeed be a contributing factor. Caster refers to the angle of the steering pivot point when viewed from the side of the vehicle. When the caster is excessive, it can increase the directional stability and self-centering of the steering, but it can also cause instability when the steering wheel is in motion, particularly as the driver attempts to straighten out after a turn.

In cases of excessive positive caster, the steering system may create a situation where the return-to-center action of the wheel is influenced by increased forces. This can lead to a shimmy effect, which manifests as a vibration or oscillation in the steering wheel as it centers. This is particularly noticeable after turns when the dynamics of the vehicle and the steering geometry come into play.

Understanding this relationship is crucial for diagnosing steering issues. While other alignments like toe settings can affect steering characteristics, the symptoms described align most closely with excessive positive caster causing the steering wheel to shimmy upon return to center.