A shaft retention and lubricating fluid delivery system and method may be used for mounting a pinion shaft to a pinion carrier and providing lubricating fluid to a pinion and pinion bearing. A retaining pin fits inside a pinion shaft radially bore and a pinion carrier radially bore to constrain the axial and rotational movement of the pinion shaft relative to the pinion carrier. Pressurized lubricant and centrifugal force from pinion carrier rotation aids in maintaining the retaining pin in a retaining position. When the pinion carrier is not rotating, a cap screw prevents the retaining pin from disengaging. An annular gap passage between the cap screw and the interior of the pinion shaft allows lubricating fluid to reach the shaft, pinion and pinion bearing.