What would cause my barely used green bearing to do this?

Unfortunately, the original Mopar Green wheel bearing design has 2 problems.

First generation (RP-400) Green bearings, still sold by Mopar Performance and others, are problematic because the crimped-on flange will not allow the bearing to wiggle around inside a housing that is not perfectly straight (none are).

In addition, the design causes the axle to be inserted DEEPER into the housing than necessary. This results in pre-loading against the differential thrust block and early bearing failure.

Second generation (MO-400) snap-ring style Green bearings are forgiving because they can move around inside the housing and they do not preload the differential thrust block in a stock application.

Most guys who have problems with Green bearings are running the RP-400 first generation version or incorrectly made aftermarket axles or housings or poorly designed rear disc brake kits, all of which cause pre-loading and premature bearing failure.

I have several customers running MO-400 snap-ring Green bearings in daily drivers. The design is no different than what came stock in millions of other vehicles, including ’60s era Mopar 7.25″ and Ford 9″ rears. (For example, see here) I do not stock, nor do I recommend the first generation RP-400 Green bearing with the crimped-on 5 hole retainer. I only carry the “loose fit, snap ring style” second generation MO-400 design.


Again, copy and pasted from Dr Diff website. The OP is using inferior 1st Gen Green Bearings.
It’s a beneficial read and upgrade to use the 2nd Gen Snap Ring RP-400 style bearing. Period