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Chassis buzz

Melmark93

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Snoopy49, Mar 19, 2020 Last edited: Mar 19, 2020
I just got my car and a couple of questions.

Do any of you experience any blurring in the interior rear view mirror at freeway speeds? My mirror seems to vibrate at freeway speed and it affects the image, blurred image.

This was posted and the thread was side tracked. Anyway, I have a bad case of it. Cops around here use black Explorers and you can't swing a cat without hitting a black Explorer. I'm always checking license plates for cops and you can't see the plates in the interior mirror.
I did not have my car when this was posted and now that more guys have their cars, have you noticed the problem?
Tire over-inflation was suggested, not the case here. In my 93 Mark VIII a change of gears from 3.08 to 3.73 exposed a driveshaft on the ragged edge of balance. At 75mph it would blur the mirror that was completely clear before the gear change. In the 500, you can lightly touch the mirror, feel the vibration and dampen it out by holding it between your thumb and finger. It seems the windshield is good at picking up chassis resonances. It could be as simple as tire balance, but usually you can feel that in your butt.
Snoopy, have you check this out any further?
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Epiphany

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I like to disassemble things.
Check to see if the set screw that holds it in place needs to be tightened up.
 
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Melmark93

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Check to see if the set screw that holds it in place needs to be tightened up.
Not even close to being the answer to the problem. the whole windshield has a subtle vibration that gets amplified by the mirror being a mass
on the end of a somewhat flexible shaft connected to a diaphragm. Short answer, I already checked that. :)
Additionally, like the GT500, the Mark VIII has an IRS, any driveshaft vibration get coupled directly to the body by the diff mount. VOODOO, care to expand on "yup".
 
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kilobravo

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Haven't noticed it in the daytime and haven't driven her after dark yet but it wouldn't surprise me. It ain't supposed to be a Town Car. :-) (and my vision isn't what it used to be, either.) <bigger grin>
 

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Epiphany

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I like to disassemble things.
The "whole windshield has a subtle vibration?"

Jeebus. Being deadened by sealant and connected directly to the body...that's an odd one.
 

kilobravo

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I thought that was strange too, Tob. The whole body would have to vibrate for that to happen and it'd have to be some pretty serious impulses I would think. Frequency could be almost anywhere, too.

Mel: Do you feel it, hear it, or just "see" it?
 

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Just go faster
 
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Melmark93

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I thought that was strange too, Tob. The whole body would have to vibrate for that to happen and it'd have to be some pretty serious impulses I would think. Frequency could be almost anywhere, too.

Mel: Do you feel it, hear it, or just "see" it?
You can't feel it until you touch the mirror. It feels like a tiny vibrator and if you slightly increase the pressure, it dampens the vibration and clears the image. A sheet of glass clamped at the edges can vibrate like a drum head. The Mark's differential shake was creating a resonance in the floor pan that was transferred to the windshield and blurring the mirror. An aluminum performance shaft cured the problem. I'm wondering if the 500's carbon
fiber shaft is built to the same specs (9000 rpm) as a good aftermarket aluminum shaft. Like Snoopy & I have observed, if you have it, you'll know it and if you don't, it's hard to explain the symptoms.
 

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Check to see if the set screw that holds it in place needs to be tightened up.
This solved my problem, I was able to get about a half turn on that set screw and haven't noticed the blurring since then. The blurring on my rearview mirror was very noticeable and made the mirror almost useless. If I remember right, Tob was the one who made the suggestion.
 

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Melmark93

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This solved my problem, I was able to get about a half turn on that set screw and haven't noticed the blurring since then. The blurring on my rearview mirror was very noticeable and made the mirror almost useless. If I remember right, Tob was the one who made the suggestion.
Double checked the screw and it is rock solid. Might be the tread blocks on the Michelin tires.
The Nittos NT555G2(s) on my 13 GT buzzed like knobbys up to about 40mph then went quiet,
but never vibrated. Dealer will be thrilled with a NVH complaint.
 

Epiphany

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I like to disassemble things.
This solved my problem, I was able to get about a half turn on that set screw and haven't noticed the blurring since then. The blurring on my rearview mirror was very noticeable and made the mirror almost useless. If I remember right, Tob was the one who made the suggestion.
I did.
 
 




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