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On 11/06/2012 we were notified by a customer that they wanted a service credit of $20,000. The service credit was for machining of the front wheel spindles and bearing races for an ore hauler dump truck (used in mining) to bring them back into specification. Upon inspection, it was determined that these components had worn beyond specification. The customer wanted a credit because they mistakenly thought that the spindle damage was due to rotation of the bearing race against the shaft, which is not supposed to happen. This is not what occurred - however the customer misinterpreted evidence showing score marks on the spindle and on the inside of the bearing race.This misinterpretation occurred because they did not have complete information about the problem. The wheel group required machining because during a scheduled rebuild, the spindles were discovered to be worn beyond specification. The rebuild process requires that the spindles be returned to original tolerances as outlined in the specification. It was determined that the wear was the result of downward pressure on the spindles/races along with slight side-to-side movement. This movement happens when the truck travels from the load site to the dump site. The length of the trip, the condition of the road, and the frequency of travel are all factors in the magnitude of the spindle/race wear.
Movement also occurs when the truck is being loaded. If large pieces of rock are loaded first, and particularly if they are dropped from height, the truck will rock back and forth which causes wear on the spindles. This is a progressive phenomenon - it's less at first, and then the wearing accelerates as the gap gets larger. The spindle material hardness as well as the fit between the spindles and races are also factors, however neither was out of specification.
Two areas were hypothesized as potential causes of the scoring/wear: 1) Scoring during disassembly of the wheel group or, 2) Scoring during installation. Evidence shows that neither of these was a factor.