[Fot] TR4 axle shafts

[Scott Janzen]

I know of at least one TR racer that has just gotten the modified axles from
Southwick, and had a local machine shop do the axle housing modifications.
This would avoid the need to ship the whole axle assembly.  Not sure what sort
of jig is needed to get the housing ends in the correct position for welding -
perhaps the axles themselves?
The axles are available from a number of circle-track aftermarket suppliers -
quite possible they could be modified locally as well, and a quick search
indicates they are about $300/pair. If they have to be bought from the US
anyway you might as well have Southwick do it and send them to you.  They
might be able to supply the axle housing ends as well.

Southwick Machine
Coal Valley, Illinois
Robert Southwick
robsouthwick at gmail.com

On Jan 19, 2014, at 8:54 PM, Tony Drews wrote:

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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