When I get stressed out my temper rises to the blow off point and I go boom:-k:angry5:
No okay, when you're talking shafts, whenever you change the diameter of a shaft from one dimension to another (either smaller or larger) that point of intersection becomes a stress point. If something were to come along and smoke that shaft in all likelyhood it would break at that point. The 489 pinion necks down from the large support bearing to the small but the 742 is very pronounced with an actual machined 90deg shoulder. The 741's shaft is almost the same dia from bearing to bearing. I'm not saying a person will ever break an 8 3/4" pinion shaft but the weakness is there. Myself I've never seen one break there, I have seen them snap off up at the yoke spline. This is also very important to crankshaft rebuilders if they've done any resurfacing or machining on the main journal or rod throw. Before their job is complete they must insure that the fillet is the right contour and chamfered properly or snapola she'll go.