As well known in involute gearing, perfect involute gears never work perfectly in real world. Flank
modifications are often made to overcome the influences oferrors coming from manufacturing and assembly
processes as well as deflections ofthe system. The same discipline applies to hypoid gears. This paper, first
of all, presents an approach on validating FEA predicted axle system deflections. Next, influences of axle
deflectionsand typical flankmodifications(lengthwisecrowning, profilecrowning and twist) on contactpattern
and stress distribution of the hypoid gear set are simulated by using an example face–hobbed hypoid gear
design. Finally, two groups of experimental hypoid gear sets are made with two different designed flank
modifications. Actual tooth surface topographies are examined by using a Coordinate Measuring Machine
(CMM) to assure the desired flank modifications are achieved. These experimental gear sets are tested to
investigate the impact of flank modifications on actual gear life cycles. Test results of the sample gears are
reported to illustrate the effect of tooth flank modifications on contact fatigue life cycles.