Which of these is not a possible cause for an increase in steering effort?

An increase in steering effort can be attributed to several mechanical issues in the steering system, but worn ball joints are typically not one of them. Ball joints primarily serve as pivot points between the control arms and the steering knuckles, allowing for the smooth movement of the suspension and steering assembly. When ball joints are worn, the primary effect is often play or looseness in the steering, which can lead to a less stable steering feel rather than an increase in steering effort itself.

In contrast, low power steering fluid results in a lack of hydraulic assistance, making it more difficult to turn the steering wheel. A stuck steering mechanism can create severe resistance to movement, also leading to increased effort required to steer. Lastly, worn tie-rod ends can affect the steering response and alignment, potentially causing tighter steering which could increase the effort needed to turn the wheel. Each of these issues introduces friction or resistance, raising the overall effort required to steer the vehicle, unlike the effect of worn ball joints.