This is the race from one of the rear differential bearings on my F150, 9.75 3.55L gear. Both diff bearings and both pinion bearings are in similar condition, suprisingly the axle bearings are in decent shape (they're being replaced anyways).

This truck has 76K miles on it. I have never towed anything or overloaded it, pretty much all highway miles. Any opinions? I figure either the set-up was wrong from the factory or the bearings were defective to start with. Kind of a bummer

 

They probably just wore out. A roller or something got scored and all hell broke loose shortly thereafter. It happens. Throughly clean the housing before going back together with the new stuff.

 

The condition is called spalling and is from over preloaded condition of some bearings. More than likely, either the pinion bearings or the differential side bearings were over preloaded. The reason for the other set of bearings being spalled is due to the massive contamination that has ran thru it.

If you're diff. has never been touched; this should be a warrantable failure. I would wager she was making alot of noise, especially recently.

 

76K is out of factory warranty.

 

My guess is the bearings were set too tight from the factory. The backlash was .011" and the pinion pre-load was 16 in/lb and that was with the worn out bearings, I assume that when the bearings were new the specs were even tighter.