[Fot] TR4 axle shafts

Sun Jan 19 20:02:56 MST 2014

There is NO way to make the stock style rear axles up to competition
standards.  One of the big issues is the key.  A flexing hub will allow the
key to rotate a bit in the keyway.  The pressure of the key can crack the hub
and "away you go"... As I said, there's no way to make this better, however if
you spend a bit of time using some valve lapping compound on the tapers to
make them as close to parallel to each other and smooth, you can reduce the
flexing of the hub/axle taper interface.  Apply compound, remove key, rotate
til your wrist hurts, clean tapers, install key and pray...

hubba hubba....
Nick in Nor Cal

ps. Dont use the early style axles that are one diameter from the splines out
over the length of the axle...they twist and break at the spline/axle
edge...use the later axle with a smaller diameter next to the splines and
larger at the hub end...they're more resistant to twisting!  Back in the day,
I used to check the axles on a regular basis and change them out when the axle
twisted one whole spline!!!

-----Original Message-----
From: Tony Drews <tony at tonydrews.com>
To: MadMarx <tr4racing at googlemail.com>; fot <fot at autox.team.net>
Sent: Sun, Jan 19, 2014 5:54 pm
Subject: Re: [Fot] TR4 axle shafts

The stock design solid axle will flex in the tapered portion where
the hub is pressed on.  The car I rolled had stock design axles but
made out of very good steel and stock design hubs also made out of
very good steel.  They were manufactured so that the "stress risers"
were removed, but under load the axle, about 1/3 of the way inboard
of the outer nut, starts to flex.  You can see the fretting inside
the hub where that happens.  It bends over and over until it breaks.

The "Southwick Rear Axle Conversion" uses Ford 8" axles that are cut
down in length and re-splined for the TR-differential.  The outer end
of the axle tube is cut off and the outboard end of a Ford 8" axle
tube is welded on.  It is possible that someone sells just that outer
end of the axle tube.  The backing plates are machined in the center
to have a larger diameter hole and holes are drilled for the 4 bolts
which hold the axle bearing into the housing.

These axles are a one piece design - the hub / flange is part of the
axle shaft.  The outer bearing is pressed on and an inner retainer is
pressed on to hold the bearing in place.  It is a sealed bearing, so
acts as the bearing AND the outer seal.  There is an o-ring which
goes around the outside of the bearing to seal that area too.

Those axles don't normally break.  Stock Car racers bounce them off
of concrete walls and just bend them.  And, if they DO break, they
break between the outer bearing and the differential so that the
wheel stays on the car.

I'm describing all of this so that it may help you or give you
ideas.  It would be good for someone in Europe to do a similar axle
conversion for the Triumphs.  I get occasional messages from someone
overseas wondering how they can have that conversion done.  Right now
it involves sending an axle housing to Southwick Machine and Design
and having them send it back.  That's expensive in the US and TOO
expensive for someone not in the US to do.

We came to the conclusion that any design with a separate axle and
hub comes with the possibility of having the hub and wheel separate
from the car.  I'm sure that with beefy enough parts of a good design
that this problem can be overcome though.

Tony Drews

At 04:29 PM 1/19/2014, MadMarx wrote:
>To get more knowledge about the TR4 axle this weekend I did the engineering
>calculations about the axle shafts in search to solve the question:
>
>Why do they break?
>
>I found out that on a stock TR4 the axles don't meet the safety margin
>required by German design rules.
>
>You need a safety margin on 1.5 and the axle with everything stock meets
>only 1.32 which might count off some miles of that axle on heavy road use or
>trackdays.
>
>On a race car it gets worse. My TR4 can do 1.5Gs on low speed corners. That
>is  quite a lot more than for a road car.
>
>The safety maring should be at  a factor of 1.5.
>On my racer it is 0.9 which means the axle WILL break! You need 1.0 to be
>just on the edge with break from overload.
>So the axle has very good reason to let go and the stock material must be
>excellent to withstand racing for a while.
>
>I calculated with 42CrMo4 which is a superior steel for axles, the 2nd best
>available in ancient times.
>
>So the way to go for me is with an new design that fits plug and play into
>the stock housings.
>
>I will take the TR2 shaft design as rough pattern but a lot stronger for
>racing purpose.
>
>I tell you if I will be successful.
>
>Cheers
>Chris
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