Dave and fellow listers,
I'd like to add another perspective, if I might. Comments IMHO as solicited
by the original e-mail. I guess you can file this under the "alternative
paradigm" heading. There's a point here, but you'll have to bear with me
through the next paragraph.
I've worked in a job in the pharmaceuticals industry that's allowed me to
work on teams involving many of the different disciplines that are needed to
make a drug -- chemists, biochemists, biologists, MDs, clinical research
specialists, MBAs and so on (I'm an economist by training). When we get
together, I've noticed that each person tends to view a problem and its
solution through the lens of his/her training.
The point? I can see how a metallurgist would tend to view failure of the
material as THE cause of the pins breaking. I am reminded of my work
experience because some time ago, I held a replacement pin from Dale A and
the OEM pin in each hand while talking to my father-in-law, a mechanical
engineer by training and profession. His first reaction was to the design
of the pins, not the material.
He thought that the OEM example was inherently weaker in its design, most
acutely so in the narrowed areas for the mounting bolts. Not the case with
the replacements. I'm not going to give his name or pedigree, as I haven't
asked his permission to involve him in this debate, and don't plan to ask
him to conduct a formal analysis.
The new pins (which are of 4130, rather than the more brittle 4140 steel)
are installed on my crossmember. I plan to run them, with the matching
Delrin bushings, when it's all back together. Perhaps other listers having
more experience with this setup can comment further.
I'm also planning to change the Ackermann angle of the steering. Rich, do
you think your friend in Washington with the rack that retains the Alpine
steering geometry could be persuaded to provide schematics to one of our
enterprising suppliers?
Food for thought,
Brian
----- Original Message -----
From: <DJoh797014@aol.com>
To: <tigers@autox.team.net>
Sent: Wednesday, October 10, 2001 11:27 PM
Subject: Delron bushing warning
> Fellow enthusiasts, The following is written with my
> sincere belief it may save a life. Comments welcome.
>
> DELRON BUSHING WARNING!
>
> In 1974 while doing about 70 mph on QE2 just north of Lake Ontario, the
> right lower fulcrum pin in the A-arm suddenly broke. It was all I could
do
> to control the car. I am one of few to survive such a break.Two years
> earlier I replaced the original rubber/steel sleeve bushings with delron
but
> reused the original pins after magnafluxing them. I had the broken pin
> examined by an expert metallurgist. His professional opinion was the pin
> failed with a twisting fracture most likely caused by lack of lubrication
and
> the pin not rotating in the bushing. Fortunately other than the A-arm and
> fulcrum pin, the Tiger was not damaged.
>
> I replaced the right A-arm and replaced both fulcrum pins with 4140 super
> strong pins. I used new delron bushings that I lubricated well when I
> installed the pins. The A-arm rotated easily around the pin before I put
it
> on the car. Every spring, as part of my preseason check, I lubricated the
> pins
> and checked for ease of movement.
>
> Last fall while my son was making a left turn, the right fulcrum pin
suddenly
> broke again! There was no way to steer the car. He hit an Explorer on
his
> right, rolled it over and totaled it. He then took down a light pole
spinning
> around the concrete base while the pole was in the air. He was not
injured
> because he was wearing a seat belt. My insurance company totaled the car.
I
> am now in a painfully slow process of acquiring the parts I need.
>
> When I found part of the fulcrum pin at the accident scene, I knew what
> happened. I took the broken pin back to the same metallurgist. After
> examining it he concluded that the pin was indeed a 4140 pin and that it
did
> not fail with the twisting fracture he saw 14 years earlier, but failed
due
> to an excessive load being applied to the pin. He felt that most likely
cause
> was the delron bushing transmitting excessive loads to the pin under
certain
> conditions and cracking it. This process would continue (perhaps for
years)
> until without warning the pin would fail and loss of steering would
result.
> He felt that the original rubber/steel sleeve bushings provided some give
> that helped protect the fulcrum pins. A fulcrum pin would be less likely
to
> break in this type of bushing than in delron. Though he would not say
that
> there was no possibility of a pin breaking in original style bushings. He
> also felt that lubricating the pins, while addressing the twisting
failure,
> did nothing to address this type of break. He emphasized greatly that
EVERY
> PIN WHETHER, STOCK STEEL, 4140 STEEL, TITANIUM, ETC WILL FAIL WHEN USED
WITH
> DELRON BUSHINGS. He said again EVERY PIN WILL FAIL. He asked me to warn
all
> owners.
>
> His qualifications include: PHD in metallurgical engineering, over 20
years
> doing industrial failure analysis, senior member of the American Society
> for Metals, received the 1999 NACE International Award for outstanding
> contributions to science, has co-authored two books on failure analysis
that
> are used as the standard textbook at most engineering schools, and has
done
> over 3600 failure analysis. He is an expert in the field.
>
> Short of redesigning the entire front suspension he recommends that if you
> are using delron bushings you should be very aware of the risk and make
plans
> to replace the bushings with the original style as soon as practicable.
> You can reuse the fulcrum pins but only after having the fulcrum pins
> magnafluxed and microscopically checked for cracks, particularly in the
> shoulder area. If you are using original style bushings you may not be
> at risk now, but NEVER replace them with delron. Personally I have
purchased
> another set of 4140 pins and will install them using new polyprolene/steel
> bushings.
>
> Delron bushing are meant for racing applications. This means that as part
of
> the preseason checkout, the pins should be removed and magnafluxed. They
are
> NOT meant to be installed and the pins never checked again. If you insist
on
> using delron, you must check and magnaflux the pins often no matter what
the
> pin is made of.
>
> If you think you can ignore this, I recommend you read the metalurgistbs
> qualifications and his recommendations and base that against what makes
you
> think you can ignore him. Remember what happened to me.
>
> Dave Johnson B382002668(under repair) Aurora, IL
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