The road tractor in Figure 1 was involved in an accident with another vehicle on an interstate highway. The insured driver complained of complete loss of control, suggesting a mechanical malfunction as a cause of the accident. Inspection of the steering wheel revealed a total lack of resistance while turning it right or left.


Figure 1

Figure 2

Inspection of the steering linkages revealed the steering arm of Figure 2 with a failed ball joint that was no longer connected to the drag link (a bar connected to the steering gear that turns the wheels right or left.) Figure 3 is a close- up of the ball joint showing a pitted and corroded surface of the ball joint (arrow).


Figure 3

Figure 4

Figure 4 shows the other end of the ball joint that was attached to the drag link. Examination of the joint suggests that lack of lubrication caused the failure. The joint is a sealed joint and does not have a grease fitting. With over 360,000 miles on the tractor, this failure is characteristic of wear-out of the ball joint assembly. Over time, seals on sealed units fail with loss of lubricant or contamination of the lubricant. As friction increases in the ball joint, severe wear takes place until the ball joint stud is not captured by the socket, resulting in steering failure. Periodic vehicle inspections should discover worn joints. Also, a driver familiar with the vehicle should note sloppiness in the steering while operating the vehicle. In this case, the insured performed the vehicle inspections obviating any chance of subrogation.

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