Broken Theory


R. Scott King, BSME ::::

Case Synopsis: A commercial vehicle operator was fatally injured when his truck overturned at the bottom of a long descent. After the incident, investigators discovered that four of the truck’s eight brakes exceeded their re-adjustment limits and concluded this as a contributing factor. Upon learning this, the vehicle owner researched his maintenance records and found that the culprit brakes had been replaced by an independent service provider approximately 4,000 miles earlier. Subsequently, a suit was brought against the defendant repair shop alleging defective vehicle maintenance and service.  In his liability report, plaintiff’s expert concluded that the subject brakes could not have deteriorated to their post-incident condition unless they were improperly adjusted during the recent service. Defense experts agreed the brakes were out of adjustment, and were a contributing factor, but made several key points during trial that reduced plaintiff’s theory to guesswork.

Expert Analysis: First, defense experts taught the jury how truck brakes operate, and how and why normal brake component wear changes brake adjustment. Specifically, the jury understood that changes in brake adjustment vary according to many factors such as load, driving style and driving conditions (factors that were all undefined in this case) and thus could appreciate the importance of quantifying these factors to help differentiate between normal brake wear and the alleged defective service.

Next, defense experts used the truck’s service chronology to demonstrate that at the time of the incident, the truck was near its historic brake readjustment schedule. This testimony helped reinforce the concept that some level of brake wear, and the corresponding need for readjustment, is normal and expected. Moreover, defense experts used a DOT study attached to plaintiff’s expert report indicating that truck and fleet owners are, through their own experience with their own equipment, best situated to know when their brakes require adjustment.

Finally, defense experts explained that despite inspecting the subject truck several times, plaintiff’s expert did not measure the brake adjustment, nor did he perform any disassembly or any measurement necessary to quantify the amount of brake component wear alleged to have occurred between defendant’s service and the time of the incident. Defense experts argued that such measurements were critical to plaintiff’s theory and that short of performing them, he could not tell the jury specifically what the defendants did improperly.

Result: After deliberating for two days, the jury returned a defense verdict.

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Categories: Case Studies


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