A spiral bevel gear and pinion set that showed "excessive wear on the pinion teeth" was submitted for analysis. This gear set was the primary drive unit for the differential and axle shafts of an exceptionally-large front-end loader in the experimental stages of development. There was no evidence of tooth bending fatigue on either part. Several cracks were associated with the spalling surfaces on the concave sides of the 4820H NiMo alloy steel pinion teeth. The gear teeth showed no indication of fatigue. The primary mode of failure was rolling contact fatigue of the concave (drive) active tooth profile....