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  #1  
Old 01-26-2009, 09:43 PM
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Location: central illinois
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Angry squeal under dash

I wrote about this before but I have more info..1990 300 SEL 125000 miles.
I have a squeal that starts at maybe 40 or 35 mph and quits at 58-60. Today it didn't start until 45 and quit at 55. Somedays it doesn't squeal at all. I cleaned out all leaves caught in the cowling thinking it might be that.
Is there any vacuum hoses or something that runs into the dash that may have a leak? I know its not a fan motor and the speedometer that has been eliminated but this problem is driving me crazy. In all my Benz', I have never had this problem. HELP

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Old 01-26-2009, 10:10 PM
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Can you pinpoint what area of the dash it is coming from? I'm pretty familiar with the guts of that dash.

You're right about it NOT being the speedo. On that car, a noisy speedo manifests as clicking noises that sound somewhat similar to a turn signal left on as you approach 50mph......

Are you certain that the climate control isn't on when this is happening? There's a tiny air sampling blower located to the right of the passenger's foot well. It's on anytime the climate control is on. The bearings like to dry out and start squealing.

See if you can pinpoint what area it is coming from and the status of the various controls when it happens. Post back.


-tp
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  #3  
Old 01-27-2009, 12:41 PM
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the squeal sounds like it is coming from the middle of the dash up high
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Old 01-27-2009, 07:29 PM
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I can have the climate controls off or on it doesn't make any difference
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Old 01-27-2009, 09:04 PM
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Geez, that's odd. Not too many components in that spot other than vacuum pods that control the climate control flaps. I guess it is possible that you have a vacuum leak there.

If you track down the vacuum line that feeds that system and plug it, you can see if it then goes away. If so, you have a vacuum leak.

Does pushing the throttle hard make it stop? That might indicate a vacuum leak as well.

The only other thing I can think of is that the seal at the bottom of your windshield is shot and you are getting air blowing past it making noise, but that is really a shot in the dark.

-tp
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  #6  
Old 01-27-2009, 09:36 PM
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Are you sure you aren't hearing a belt squealing? I can't think of anything in the dash area that would squeal like that.
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Old 01-27-2009, 10:54 PM
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Yeah, sure beats me. I can't think of anything that would squeal.


1) How loud is this squealing? Does it sound like a belt, and are you familiar with what a belt would sound like?
2) Is it engine RPM dependent? Does it happen only when driving, or can it happen in neutral if you rev the engine?
3) Does it sound metallic like a dry bearing in a pulley?

-tp
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Old 01-29-2009, 05:21 PM
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No it is not a belt squealing...it does not always do it either. Sometime the squeal is faint n sometimes it does not do it ... i still think it is a vacuum leak somewhere but the windshield seal does intrigue me though. As I am driving it sounds like air moving thru a very small space and as I slow down the noise decreases until it disappears at 40 ( it always disappears at 55-60)
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Old 01-29-2009, 07:08 PM
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On looking at my 126, I realize now that the hood really does cover most of the area at the base of the windshield, though I guess air could still be getting past. Check the rubber boots that go around the windshield wiper arms. Just a shot in the dark.... Dump a few cups of water down that grill and see if that changes things. There might be something under there that is buzzing like a reed. I wish I could hear this sound......

Next time you hear it and you have a chance, punch the gas. If the sound disappears immediately, it might point to vacuum leak since engine vacuum is very low at wide open throttle.

Also, look down inside your defroster vents. Maybe something got in there....


-tp

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