I think the real issue is the inner pinion bearing. the 742 has a larger bearing and a 489 is even larger. these are Timken bearings that control the thrust on the pinion. the larger bearing will have more control and less deflection......
1. I don't think small bearing size differences have any bearing (pun intended) on r&p deflection issues being mentioned here.
2. Not sure what you mean exactly on referring to "larger bearing", since I believe as shaft size increases the actual roller bearings get dispersed in a smaller area, since outer race dia remains the same(?), not sure how that has any impact on r&p deflection issue.
3. This means to me a 489 with a larger pinion dia shaft has less capacity bearings then the 742, but not sure that is an issue anyway with "thrust" overload, leading to likely failures
