[Fot] TR4 axle shafts

[Van Mulders Marcel]

Some years ago I looked at an inside car video of Tony Drews accident and at
pictures of the car and the broken axle shaft. Very impressive! It's very
credible that bending of the part of the axle shaft that is inside the hub
is the cause of the failure.
If the  fretting of the axle shaft in the hub is going on for some time
before it breaks, it would be interesting if one can find signs or
indications of that fretting and thus failure of the axle shaft pending :
i.e. the nut being not very tight, removing of the hub being possible
without much force,being able to move the hub onto the axle shaft (by trying
to turn a the wheel)...
If the nut is very tight and the hub doesn't move with some force of a hub
puller, would it be unwise to assume that the axle shaft is not fretting and
that it won't break in the near future?
PS : The early sidescreen TR's (TR2's and some TR3's) had the weak Lockheed
axle intead of the later Girling axle. The lockheed axle shafts did break by
twisting of the shaft, not by bending : it was possible to break a Lockheed
axle shaft by letting the car roll backwards of a hill, and, with the box in
1st gear,engage the clutch with a enough throttle.
Marcel, Belgium
-----Oorspronkelijk bericht-----
Van: fot-bounces at autox.team.net [mailto:fot-bounces at autox.team.net] Namens
Tony Drews
Verzonden: maandag 20 januari 2014 2:54
Aan: MadMarx; fot at autox.team.net
Onderwerp: 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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