[Fot] TR4 axle shafts

[Tony Drews]

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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