the pinion snubber keeps the driveshaft from rubbing in the driveline tunnel when you overload it with your 300# inlaws in the back seat--one of my buddies told a story of going to a rock concert with 5 friends and all their camping gear in a 58 chevy wagon and the driveshaft rubbed for about 900 miles until it broke---and they were still about about 500 miles out---chevy didnt use the snubber back then---- if you have a drag race car or watch the videos---when the car takes off the rear end goes up (normal suspention) that is unless your 300# inlaws are in the backseat for traction-- then all bets are off-----back on the SAE test kit was 1964 and ford had ALOT of engineering to learn before the 9 got equal----and it was the AFTERMARKET effect that caused the impressive gains by the 9 inch not ford.....and all you young guys are kind of lost in the apples and oranges comparisions when you think you can plug and play 1960 tech vs 2010 tech----its like agrueing 392/426 hemi versus a vortec or an all aluminum 572 crate motor----or in simpler words my nfl linebacker son can beat the crap out of your grandfather----so there