NHTSA Engineering Analysis EA11011

ODI opened a Preliminary Evaluation (PE11-007) based on one fleet report alleging it had experienced multiple wheel-end fires involving the subject vehicles.The fleet believed the fires were due to a power spring fracturing and puncturing a brake chamber diaphragm resulting in a loss of compressed air to the brakes.The loss of air was believed to cause the brakes to drag and overheat.ODI upgraded PE11-007 to this engineering analysis to further evaluate the cause of the wheel fires and assess the scope, frequency, and safety consequences of the alleged defect.After a comprehensive review of the data related to brake chamber failures or replacements on the subject vehicles, ODI did not identify the existence of a safety related defect trend.Of the two vehicle fires initially reported, only one was subjected to a fire investigation.The fire investigator in that case could not identify the component responsible for the vehicle fire.Driver statements reviewed from one fleet which experienced two brake overheating events indicated that the vehicles had not been operating at normal air system pressure levels prior to the events.In addition, the failed or replaced chambers had been in service on average nearly 50 months.ODI reviewed 477 warranty claims and fleet reports of brake chamber failure or replacement.From the data review, three (3) brake overheating incidents involving a subject size 24/30 failed brake chamber were identified.In reviewing the time in service for the overheating incidents, it was found that vehicles had an average of 50 months in service.This time in service represents a typical service life wear out.The injuries reported in the opening resume for this investigation are no longer being considered as having resulted from the alleged defect in the subject brake chambers.In the case of the smoke inhalation originally reported, the fire was not determined to have been caused by a failed brake chamber.In the case of the injuries that resulted while repl