Delete now if you're sick and tired of all this axle talk. Otherwise,
especially if you're a technophobe, read on.
Every hub / axle assembly that I've taken apart has exhibited a puzzling
thing. The surface appearance of the axle on the inboard third of the
mating surface has been different than the outer 2/3 or so. I never
understood why this was. Furthermore, with the new axles and hubs, this
same effect was noted and was disturbing to some folks. To others, like
me, since I did not have an explanation, and since the old parts looked
like this too, I dismissed it.
Switch gears with me for a moment. To have a fatigue failure, you have
to repeatedly bend or stress a part. These failures down inside the hub
are all fatigue failures. How can the axle be bending down inside the
hub?
If you look at a cross section of the HUB / axle assembly, you will note
that the flange where the wheel bolts on is at the same position on the
OD as the end of the axle keyway occurs on the ID. I think that this
flange makes the hub such a large diameter at this point, that from the
flange outward the axle and hub act as one part, as intended.
Inboard of the flange, at the seal diameter, the hub is a relatively
small diameter. I think that under heavy cornering loads, when this
whole thing tries to bend, the hub ID opens up slightly (kind of
bell-mouthing) and allows bending inboard of the wheel flange. This
bending starts at the end of the keyway, explaining the different
surface appearance of the axle. It's actually rubbing from here on
inboard. Unfortunately, the area where it starts to bend is right at the
end of the keyway, with its sharp edges, so a fatigue failure starts.
Therefore the problem is not a metallurgy problem, but rather a parts
design problem that is exceedingly difficult to overcome. Wonder what
the SCCA would think of all that?
Anyway, that's mah story an ah'm stikkin to it.
--
TR6 -- 29 and still running
TR4 -- 39 but no longer racing
uncle jack -- temporarily sidelined
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