I sending my pics and article to a victim now. If I am successful
I'll send to all who asked. In the meantime here's some more
thoughts: Dave
Dr. Herro has over 35 years and 360 professional failure analysis, and the
author the standard textbook for failure analysis used in universities today
After my first pin break I felt the cause was the pin seizing in the delron
bushings
that I put in a few years before. Dr. Heero said my break was not caused by
rotational force but by a shearing force. I replaced the A-arm and both
lower pins
with Doug Jennings pins and new delron bushings.
Fast forward 16 years, and the right pin broke again. This time my son was
making
a left turn at a light. He said he could not steer the car. It hit an
Explorer, rolled
it over, totaling it, and then took down a light pole. He was not injured
and the
car is still under repair. At the scene, I found the end of the pin with
nut, lying
in the road. I knew the what had happened.
Dr Herro examined the pin with his electron microscope and said bThis pin
also
broke because of a shearing force. See these ridges. These are called
Chevron
Ridges and occur each time the pin cracks. Eventually the load exceeds the
strength of the pin and it fails catastrophically forming a crystalline
structure.
The break occurs at about 600 ft/ second or in about .00009 sec. Itbll
break
before you hear it. He also said the pins was indeed made of 4140 strong
steel
as Doug had said.
I showed him Tom Hallbs fixes for lubing the pins. He felt they were good
but did not address the shear loading evidenced. Also the problem of the
mounting bolts remained.
I showed him John Loganbs designs. He said these were better. It provided
an
extra level of strength and a good margin of safety for when the pin breaks
by
supporting the cross member. The design also eliminates the mounting bolts
issue.
But he said I cannot endorse any fix without doing a failure to destruction
analysis. This will take time and money and many front ends.
He also added, bTell your friends to never never powder coat or heavy paint
suspension and steering parts, because the coatings hide cracks or worse
fill cracks. The SCCA and most racing bodies concur.
He concluded: bTell your friends to be very careful until they fix their
cars.
Wear their seat belts. Beware of changes in handling especially after
backing.
There is nothing they can do to prevent a failure. The problem is inherent
in
the design. If they are truly worried he will gladly buy their cars at say
$200
each and eliminate their worries.
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