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  #1  
Old 07-05-2010, 08:23 AM
1985 190d
 
Join Date: Nov 2006
Location: canadian border vermont
Posts: 518
squealing while under way

Took a long trip this weekend; about 300 miles/day in three legs. Car ran perfectly the whole trip except for the following, which tightened my cheeks when it happened:

Going about 55, heard a terrible squeal and pulled off the road. Squealing continues so I turn off the engine. Restarting was without incident; I have oil pressure, good temps and no alternator light, so I conclude its the ac compressor. No choice but to keep driving. We drive another 150 miles without a/c. It happens again without ac, so I finished the trip with the ac on. We thought it was coming from the rear. Both moving and stopped. I cant say if it was related to the engine running or not. Sunroof was closed, radio antenna was down, and doors were locked the second time and not the first.

But I'm thinking its the aux vacuum pump. It was loud. It wasnt the running gear. Why would it activate and how do I test this theory? I tried the locks a dozen times at home but couldnt recreate. Could the antenna decide to lower itself when already lowered and scare the stuffing out of me? Anybody want speculate? (I know you do!)

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  #2  
Old 07-05-2010, 01:35 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,642
we certainly do love to speculate here, don't we?


I would keep a systematic approach about removing variables such as antenna and aux VP. Start with one, wait for the sound to reappear, then remove another... etc...

- - start with thorough belt and tensioner inspection.

- - I doubt the antenna, but things do happen. Around '84 and up the antennas were given a self adjusting height feature to maximize reception. To kill this feature, put the switch in the fully 'up' position.... or if you don't use the radio unplug the antenna in the trunk.

- - if the noise is still occurring, unplug the vacuum pump. This one sounds unlikely as well. Some forum searching might reveal previous episodes. I was under the impression it only ran when the car was off and when required.



Don't neglect other spinning accessories like the power steering pump and alternator... these can get noisy as well

Last edited by jt20; 07-05-2010 at 02:03 PM. Reason: clarity
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  #3  
Old 07-05-2010, 02:36 PM
Renntag's Avatar
User Especial
 
Join Date: Jul 2008
Location: Kona, Hi
Posts: 1,396
I am confused.

Title states "under way"....the sarcastic side me would suggest to go "overway" instead. LOL.

The description then states alot of sitting still. start in one area. get the noise to reproduce. When it does, put the trans in neutral, allow rpms to raise and lower. Does the pitch change with RPM? Then the squealing is coming from an accessory or a motor component.

use a stick or rod. Touch one end to each accessory and the other end put to your temple or skull. The noise will radiate to your ear and be loudest when you are closest to the culprit.

be mindfull of the belts and cooling fans (the alternator has a fan as well).

If considering the power steering pump, does turning the steering back and forth effect the sound? (not just by effecting rpm as the pump creates load) Does the sound get worse?

best of luck.
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  #4  
Old 07-05-2010, 02:54 PM
1985 190d
 
Join Date: Nov 2006
Location: canadian border vermont
Posts: 518
To clarify: noise occurred when going down the road. Pulled over and stopped moving, noise continued. Restarted car no noise. Of course with a loud squeal in your head, its hard to think of everything at once. So when the noise stopped I dont recall if the engine was running or not, but I think it was.

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