MG Car Club of South Australia
TeCnical TopiC
By ..Bob Schapel
T
AXLE BREAKAGE
here is a modification which can be
done to reduce the chances of
breaking an axle (half-shaft) in our older
MGs, particularly those with coarse
splines, such as T-Types. Unfortunately
the diff must be dismantled for this job to
be done.
If you have ever removed a rear axle
from a T-Type, you will have noticed the
“nicks” and wear marks on the inner
splines at the point where they exit the
diff sun-wheels.
Nicks are cut by the sharp edges at the
ends of the hard, square sun-wheel
splines. Nicks and wear-marks are
“stress raisers”, where cracks will start
much more easily. Gently driven cars
might only show wear marks, while hard
-driven cars will show pronounced nicks
because axles wind-up slightly when
power is applied.
In TCs, where the axles have splines of
the same size at each end, they break
more often at the inner end, despite the
outer end having the extra load of hold-
ing the wheel upright under cornering
load. This is because the stress-raising
nicks only form at the diff end. They do
not tend to form at the hub end because
hubs are softer metal which does not cut
into the axle. This is evidence that
spline nicks are a major factor in axle
breakage.
Nicks should be carefully ground or filed
out, but it is much better to prevent them
from forming in the first place. This can
be done by carefully re-shaping the
ends of the differential sun-wheel
splines, so they can no longer cut into
the axle splines.
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A Dremel tool with a small grinding
wheel/disc is ideal, to grind very slight
flairs or tapers on the sun-wheel
splines. About 30 thou’ of metal should
be ground off each sun-wheel spline
thrust face at the axle exit point.
The depth of metal removed should
then fade out to nothing, further back
along the spline, as far as tools can
reach accurately (probably less than
¼”).
The freshly ground area could then be
smoothed off as much as possible with
some emery paper wrapped around a
small triangular file. A file alone would
be ineffective on the hardened steel of
a sun-wheel.
After this treatment, the very ends of
the diff spline faces should never touch
the axle, even when the axle winds up
under power.
Although not the optimum spline profile,
this suggestion is probably as much as
accessibility and patience allows, and it
should be a big improvement. Follow-
ing such work, nicks should not form as
easily, and axles should be less likely
to break.
What would be the optimum spline pro-
file? That would be a topic for engi-
neers to debate, and would then be
very difficult to execute accurately. I
believe the best profile would be a
“flared” shape, starting at about 40
thou’ depth and then fading back into
the splines about half an inch or more.
It should allow the axle splines to wind
up progressively around the curved
face of the flair as more power is ap-
plied.