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Old 07-01-2009, 11:27 PM   #1
williaty
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Default Own PolTec Endlinks? Beware of Catastrophic Failure

I have PolTec Heavy Duty spherical bearing endlinks from the Fall of 06. A while back, I had noticed one was cracked a little bit, but other car problems pushed it out of the priority fix it should have received. Leaving it alone was a problem. Today, it failed outright, thankfully in a bump rather than a turn. If you have these parts, check them. If they're cracking at all, replace them.













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Old 07-01-2009, 11:36 PM   #2
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WOW thats insane! looks like a major stress riser is from the setscrews. i've never seen metal peel away like flaky baklava. mmm delicious baklava...
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Old 07-01-2009, 11:38 PM   #3
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I guess I know what you're doing tomorrow. I'll set some links aside for you.
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Old 07-01-2009, 11:39 PM   #4
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I guess I know what you're doing tomorrow. I'll set some links aside for you.
get one of those and send it to me clint. i gotta see that peeling. i'm in awe
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Old 07-01-2009, 11:40 PM   #5
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wow, just wow. and great pics too. i have always wonderd how long there CF lat links hold up, but looking at this i know now
get yourself some of the best ones out there, from one of the two guys above
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Old 07-01-2009, 11:43 PM   #6
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Well, since Clint saw my post, it looks like there'll be a set on my desk when I get down to TiC tomorrow morning.
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Old 07-01-2009, 11:45 PM   #7
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man......should let poltec know about this...
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Old 07-01-2009, 11:46 PM   #8
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wow, just wow. and great pics too.
Thanks. This was actually my first use of my new macro extension tubes and my new camera that has Live View in it. It's astonishing how easy macro shots like this are when using Live View. It's like doing them on an old large format view camera. Me likey.
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Old 07-01-2009, 11:47 PM   #9
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Improper heat treatment????

I have seen some 7075 peel like that, but never THAT bad
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Old 07-01-2009, 11:47 PM   #10
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man......should let poltec know about this...
Already have. Not sure if he's willing to replace them yet. Not sure if I'm willing to run them again if he is. I'm cheap, so the answer is probably yes to the second question
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Old 07-01-2009, 11:55 PM   #11
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I've only see decay like that once before. Ironically, and scarily, it was on all the nuts on a bridge in columbus. It was kind of fun to peel the layers of grain apart, until it occurred to me that perhaps I shouldn't be making the bridge any worse...

That was a few years ago. I've checked it out a couple of times a year since then, and they still haven't fixed it.

I'd love for one of the metal nuts to pop in here, and drop some knowledge as to what would cause this.
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Old 07-02-2009, 12:16 AM   #12
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well...it is severe intergranular corrosion and exfoliation

extrusions are prone to this.....milled, from cold rolled stock, wont do this
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Old 07-02-2009, 12:18 AM   #13
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I'm thinking vibration thru the allen screw, weaking the metal, then corrosion. im getting more and more iffy on some of these garage shop made parts. esp for suspension.
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Old 07-02-2009, 02:13 AM   #14
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It looks like the spacers were hitting the housings quite a bit. I'm sure that didn't help anything.

-Mike
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Old 07-02-2009, 03:17 AM   #15
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Quote:
Originally Posted by Uncle Scotty View Post
well...it is severe intergranular corrosion and exfoliation

extrusions are prone to this.....milled, from cold rolled stock, wont do this
Uncle Scotty is on the right track, but PolTec says that the links are machined from 6061 billet.

6061 alloy isn't as notch sensitive as 7075 and more corrosion resistant. It has to do with ~6x more copper in the 7075.

I've seen a problem similar to this before with 6061 forgings that used extruded blanks. Long stringy large grain structure that didn't like to have the grains cut. Nice crack initiation points.

Almost the same part and application with a cast blank had very fine grain structure after forging and didn't have the intergranular cracking problem. The machining in the area of interest for these parts was the same.

For the links shown that thread form for the set screw is one hell of a stress riser and guaranteed to cut grain structure. The hole for the bushing is bad enough.

Nice pictures Ty. What body, lens, and tubes did you shoot with and at what f.

Could you get a plan view shot of the set screw thread where you think the cracking could have initiated and as high a magnification as you can. Better than 1:1 would be great.

Edit: I don't have access to a microscope right now but some photomicrographs would be very interesting. A really screwed up heat treat could have done bad things to the grain structure.

Last edited by Web Foot STi; 07-02-2009 at 03:23 AM.
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Old 07-02-2009, 07:23 AM   #16
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Nice pictures Ty. What body, lens, and tubes did you shoot with and at what f.
Nikkor 35mm f/2 AF-D on the thinnest segment of my cheapassed-totally-manual-eBay-extension tubes. Nikon D300 in Live View Tripod mode with manual focus and manual exposure. 1/250th@f/22 with 400W/s of strobe in a medium softbox 6" away with a silver bounce panel for fill.

Quote:
Could you get a plan view shot of the set screw thread where you think the cracking could have initiated and as high a magnification as you can. Better than 1:1 would be great.
The magnification is likely possible (though an utter bitch to do without macro focusing rails). However, the depth of field will be something like 1/256th of an inch thick, even at f/22. Still want me to try? Also, what the hell are you asking for in terms of what you want to see?
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Old 07-02-2009, 09:41 AM   #17
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Wow. That's some serious damage. I'll stick with Perrin and/or Kartboy.
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Old 07-02-2009, 10:14 AM   #18
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I'll stick with Perrin
So you want endlinks that fail even faster than the PolTecs did?
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Old 07-02-2009, 10:39 AM   #19
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You guys might laugh but, with my STI suspension, I'm running Cusco's links in the front which look like factory links but, they have real ball and sockets instead of the plastic sockets in the factory ones and I'm running stock end links in the back. 24mm F/24 mm rear. So far the only problem I have is they sometimes come loose after a couple track days and I have to tighten them.

I've run Kartboys too and wasn't real happy with fitment.
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Old 07-02-2009, 10:49 AM   #20
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So you want endlinks that fail even faster than the PolTecs did?
Three years of daily driving and a season and a year and a half of autocrosses with the spherical aluminum Perrin units and they haven't failed like that.

So yeah, I'll take my Perrins over those pieces.
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Old 07-02-2009, 10:55 AM   #21
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Congratulations, you got the one set of Perrins that didn't fall apart as soon as they looked at your car
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Old 07-02-2009, 11:44 AM   #22
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So you want endlinks that fail even faster than the PolTecs did?
I"ve been on my perrins for over 4 years.. and they're still working great.. could be because we dont use salt on the roads here.
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Old 07-02-2009, 12:06 PM   #23
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Quote:
Originally Posted by williaty View Post
Nikkor 35mm f/2 AF-D on the thinnest segment of my cheapassed-totally-manual-eBay-extension tubes. Nikon D300 in Live View Tripod mode with manual focus and manual exposure. 1/250th@f/22 with 400W/s of strobe in a medium softbox 6" away with a silver bounce panel for fill.


The magnification is likely possible (though an utter bitch to do without macro focusing rails). However, the depth of field will be something like 1/256th of an inch thick, even at f/22. Still want me to try? Also, what the hell are you asking for in terms of what you want to see?
Thanks for the back story on the pictures. I picked up a Nikon PK-11A on e-bay myself along with a 35mm f/2. I'm still shooting with an old D70 body though as I spent all my camera budget on glass. Used is inexpensive, but not cheap.

I know what you mean about needing focusing rails. Metallurgical Microscopes have 3 axis stages for a reason. For my camera I picked up a Kirk rail in the used department of the local "Pro Photo Supply" store.

It would be interesting to see the grain boundaries at the thread roots and really see if the cracks started intergranular, or where the grain was cut. Also, did the crack prorogate along the grain, or through the grain?

You are right about optical depth of field at high magnification. With an unpolished specimen. You can move in and out to see things, but the photos suck. For that kind of work you need an electron microscope The smaller companies that I have worked for always have contracted that out.

I'm not a Metallurgist, but have worked with them. I'm just a dumb Mechanical Engineer.

PS: I double checked my definition of "intergranular" and came up with these two sites. First one has an ugly macro picture of Al and the second has a nice photomicrograph of 7075.

http://corrosion.ksc.nasa.gov/intercor.htm

http://corrosion-doctors.org/Forms-i...ergranular.htm

Oh and here are another thoughts of what bad things that steel set screw could do:

http://corrosion-doctors.org/Corrosi...ea-effects.htm

http://corrosion-doctors.org/Forms-E...y-assisted.htm

This dumb engineer likes this site.
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Old 07-02-2009, 02:16 PM   #24
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Quote:
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Congratulations, you got the one set of Perrins that didn't fall apart as soon as they looked at your car
ive ran perrin endlinks 4+years front and rear on my bugeye with no issues. ive never had an issue with any of perrin's suspension parts...
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Old 07-02-2009, 02:42 PM   #25
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It split with the grain. Its like like it was metal Plywood and it came apart between the layers.
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