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From dr diff site
The need for non-adjustable wheel bearings
Most of these problems can be avoided by installing non-adjustable sealed ball
“Green” wheel bearings. The name comes from the Green Bearing Company which first produced them. The company has since been purchased by
Bearing Technologies.
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