When the EVO rear differential is being punished with aggressive clutch
dumps, the thrust load on the carrier bearings is great enough to crush
the differential side cover. The factory side cover fails because the
bearing post is too thin, it was not designed to handle everything you can throw at it.
The factory part is cast iron which is quite soft and it will get crushed inward allowing the bearing to spin on
Worn out side cover. Note that the post is worn
axially .009" and radially .004" on the diameter.
When the bearing is able to spin like this it'll wear the post down both
axially & radially. The photo shown above is typical. This wear removes
any preload on the carrier bearings and actually leaves the bearings at
slack. Fact: Without preload on a tapered roller bearings there is
nothing to keep them running concentric to the outer race of the
bearing, allowing the ring gear to wander all over the place both axially
and radially in the direction of thrust. This is bad because it will make
the rear end noisy from excessive backlash and it alters the ring & pinion
contact pattern which ultimately leads to
Side cover comparison showing both bearing posts in red.
Starting with billet 4340-CR steel the new side cover is CNC machined in
house. This choice of steel is much tougher than cast iron and while
difficult to machine it is done with less than 0.0005" T.I.R. in both X &
Z axis, whereas the factory allows 0.002" total indicated runout. More
material in critical areas and larger corner radii makes the new side
cover very stout. This increased rigidity eliminates deflection of
the factory differential housing, keeping the ring & pinion gear running
perpendicular to one another even during the harshest of clutch dumps.
Note the increased wall thickness of the larger bearing post of the HD side cover.
The larger bearing post eliminates
the problem of the side cover being crushed and the new bearing
has a higher axial & radial load capacity rating as well. The outer
oil scoops effectively throw additional oil to the front pinion bearing
while the 4 oil inlets are designed to
provide additional lubrication to remove heat from the friction plates
inside the differential.
HD rear side cover $235
HD Cusco side cover
here for image.
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