This paper presents a case study in failure analysis of a final drive transmission in an off-road vehicle. The failure involved a satellite gear mounting shaft that departed from the differential assembly as a result of fracturing of a retaining pin. An investigation of the mechanical condition of various transmission components, consisting primarily of visual (macroscopic) inspection, geometrical investigation and analysis of mechanical loads, led to the assignment of two principal causes of failure. Firstly, it was established that the retaining pins installed in the assembly were shorter than required, allowing them to shift in their guide holes and assume a single-shear position. Secondly, in this position they were loaded to failure in shear by abnormally high frictional forces acting at the shaft/satellite interface. These loads were attributed to severe usage and handling of the vehicle. The scope of this case study is broadened to include a review of failure incidents, that followed in additional transmissions containing short retaining pins. An account of actions taken to address the problem from a maintenance and reliability viewpoint is also included, as are further recommendations made to the operator. (C) 2002 Elsevier Science Ltd. All rights reserved.
