What is the root of this BMW design flaw in all 3,5,7 series BMW trunk wiring looms?

Almost every BMW E39 (5-series) and E38 (7-series) and E46 (3-series) has shorts that develop in the trunk wiring loom - all in the same spot!
Here is a picture of the uniformity of the shorts: http://www.bimmerfest.com/forums/attachment.php?attachmentid (6651&stc=1&d11702112
Here is another picture from another vehicle: http://www.bimmerfest.com/forums/attachment.php?attachmentid (7281&stc=1&d12154763
And another: http://www.bimmerfest.com/forums/attachment.php?attachmentid &1502&d94537117
And another: http://www.bimmerfest.com/forums/attachment.php?attachmentid )5239&stc=1&d17334573
And another: http://bimmerfest.com/forums/attachment.php?attachmentid07223&d 25771723
And another: http://www.bimmerfest.com/forums/attachment.php?attachmentid 0762&stc=1&d52530849
I could go on (and on); but we can't figure out WHAT the BMW design flaw is. http://bimmerfest.com/forums/showthread.php?t97245
Q: Can you tell from these pictures what the BMW design flaw is?
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On 03/13/2013 06:03 PM, Arthur wrote:

yeah, it's easy.
1. the wire coating has a poor grade of plasticizer*, so the coating cracks and bending concentrated at the cracked coating will fatigue the wire.
2. they're using an elbow bend, not a torsion bend. the stress concentration at the surface of the wire coating is less with a torsion bend.
#1 is a factor of the germans being too "green" for their own good and not using good old toxic pvc. #2 is the real screw-up - they would know that one if they'd spoken to anyone who'd been around the block or had done their own testing.
* the plasticizer used in the wire coating is crucial to give it flexibility. the basic polymer insulator extruded over the wire is very brittle without it, so a plasticizer is added for flexibility. if the plasticizer is too volatile and evaporates over time, the coating will become hard and brittle per the original polymer, then crack when bending stress exceeds a certain value.
--
fact check required

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On 3/13/2013 6:27 PM, jim beam wrote:

PVC wire insulation contains a lead compound. Ano-no in Europe, even for a tiny amount in a product.
Paul
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On 03/13/2013 07:26 PM, Paul Drahn wrote:

i think that was back when they were using lead pigments - hasn't been for a while now fwiu. and lead is a no-no here too.
besides, pvc isn't exactly healthy - i think they now use something called "epdm". with the right q.c. and testing, there's no reason that insulation should have degraded, and with the right physical layout, no reason it should have been challenged even if it did.
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t!

...

...

...

...

32...

...

And maybe you've found the root cause of the problem. Instead of using decent wire suited to the application, the Europeans chose to use some green hippie wire, that not only costs more, but fails.....
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On Thu, 14 Mar 2013 06:18:22 -0700, snipped-for-privacy@optonline.net wrote:

Maybe. But why does it always fail at the same spot.
That can't be due to the poor choice of insulation, can it?
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Because if you make a loop and you open and close it over and over again, it will fail in the center of the loop where the angle of the movement is greatest.

No, as you'll notice the conductors are breaking too, not just the wire. So it's a poor choice of insulation AND stranding. --scott
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On 03/14/2013 08:23 AM, Scott Dorsey wrote:

respectfully and completely disagree on that. the stranding is perfectly fine if the insulation remains intact. once the insulation cracks, then you have substantial strain concentrated in just one spot. even fine wire high count stranding will break if subject to such a failure.
the fix is both better wire insulation that doesn't become brittle, AND re-routing to avoid the elbow bend. then you can keep using cheap wire and don't need to spend money on the expensive hi-flex stuff.
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i had the exact same thing happen in the rear door wiring in a 95 toyota camry.
Mark
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-

snip
my wife broke the inside passenger side..
i've learned to use only two fingers to pull on the handles, don't grab them.
i agree they are not very rugged... but it's about the only flaw i've found with that car (knock knock)
besides the rear door wires which i understand like the BMW is a very common spot for wires to break on this car...
and interestingly the rear door is used maybe 1/100 of the time compared to the drivers door so you would have to think there is something "special" about the way those particular wires are designed and/or built to make them break before the drivers door wires break
Mark
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On 3/15/2013 5:36 PM, Mark wrote:

The inside handles seem to be designed to break at the 8 to 10 year mark. The have a slot molded in to the highest stress point, I might add I don't see any reason for it. Other than to help the dealer sell replacement handles. Other than the door handles I'm a happy Toyota owner, had a Camry, have a T-100 still a sharp looking truck, have a Lexus and an Avalon. My wife is a persistent patient shopper, and will wait until she finds a great used car at a steal. Mikek
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Of course it can be. If BMW uses some hippie green insulation that isn't as pliable as other insulation, then the insulation will crack. We can't do a forensic investigation from some pics that don't show how it's mounted, how much it moves, what tensions are on it, etc. But I'd bet that area has more bending, tension, etc than the rest of it.
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On 03/14/2013 01:11 PM, snipped-for-privacy@optonline.net wrote:

Yes, that much is true. Someone had mentioned that having the wire in that area flex in torsion would be preferable and I agree with that statement as well. Would be simple to have accomplished by having the hole in the body offset by a few inches (actually as far as possible would be preferable) from the hole in the trunk lid, and using a correspondingly longer rubber boot. then most of the flexing of the wire as the trunk lid opens and closes would result in a slight twisting of the wire rather than a sharp bending.
The same holds true for wiring running from a body pillar into a door e.g. for power mirrors, windows, speakers, etc.
nate
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wrote as underneath snip

Have to be extra vigilant to water rundown in your scenario which for the wiring longevity agree would be much better! C+
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wrote:

As long as it doesn't fail during the warranty period they don't care.
Is this poor grade wire mandated by regulations?

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I have seen a lot of cars over the years, and I have never, ever seen one that used anything approaching quality wire.
And that begins with the '72 Datsun I had, where all of the insulation turned to goo and every foot of wire in the body had to be pulled out and replaced.
Just take a look at what goes into airplanes vs. what goes into cars and you'll be staggered. --scott
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The price per foot will probalby do the same.
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On 03/18/2013 07:38 AM, Scott Dorsey wrote:

you're spoiled if you work on aero-spec stuff.
car quality goes in cycles - for some manufacturers anyway. in the late 80's, hondas used a higher grade under the hood - fine wire high count high temp high flex [though not silicone], and it's remarkably reliable. in the mid 90's they changed to lower flex, smaller cross-section, lower count, much more akin to the wire used in the rest of the vehicle - it still just about hangs in there, though i doubt it's million mile material. i'm pretty sure copper prices had a big influence on this.

planes cost a /lot/ more!
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Did they tin it? The lack of tinning is one of the things that annoys me about many of the cars of that era.
Silicone is actually a problem for cars because if you nick the insulation the cut will propagate until it becomes a break.

It wasn't failing enough, so they had to downgrade it. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On 03/18/2013 10:38 AM, Scott Dorsey wrote:

no, it's not tinned.
there are two schools of thought on that. on the one hand, surface oxidation resistance is a good thing. on the other, there may be a problem with tin in fatigue environments. i don't know this for sure, so if you know someone at work who does, it would be good to check - but tin has a weird deformation mechanism called "twinning" which changes the surface of the metal where it's occurred. given that almost all fatigue initiates at a surface, that /might/ be a fatigue initiator. how much it might be worse than oxidation, i can't say, but i know a lot of mil spec wire is silver plated, not tin, so i think it might not be simple cheapness preventing its use.

indeed, but that's not unique to silicone - many elastomers have the same problem.

maybe. it was was bullet proof - never failed unless abused.
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