OPTIONAL HEAVY DUTY SIDE COVER UPGRADE

Strengthen the rear differential  in your EVO without going through the hassle of stuffing a different rear end in the car.

 

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 the post.

typical EVO diff side cover

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 gear breakage.

 

stock VS. TRE

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.

 

 

oil inlets to feed the limited slip

 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 $315. click here for image.

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