What could cause a pinion nut to loosen itself?
The tension on the pinion nut is maintained by the components behind it. This usually includes the two pinion bearings, sometimes a spacer and a crush sleeve. If a bearing[s] fails, additional space is created and tension is reduced. Simply tightening the nut will normally only speed the deterioration. Instead the differential should be professionally checked to determine and eliminate the root cause. Quick action can prevent an even bigger repair. For much more on pinion set up, see our article Differential leaks.
