The design and size of the pinion-gear shaft is the major difference between 741, 742, and 489 differential centersections. Below, the pen points out the beefy, tapered 1.875-inch pinion shaft featured on all 489 gearsets (regardless of ratio). By contrast, the 13⁄8-inch pinion shaft used in all 741 cases (top) clearly lacks the heft of its big brother. The 13⁄4-inch pinion-shaft diameter found in 742 cases (not shown) is nearly as strong as the 489 unit but lacks the tapered configuration. The taper eliminates 90-degree surface intersections, which are common high-stress failure points. Also, note how the larger pinion shaft takes a larger inner-pinion bearing (seen just below the gear teeth). Keep in mind that when you see a car launching with the front tires off the ground, its entire mass is being supported momentarily by these components.