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Mystery Vibration @ 3000-3300rpm 82 633csi

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BCMac
Posts: 36
Joined: Fri Apr 12, 2013 6:49 am
Location: Bellingham, WA

Mystery Vibration @ 3000-3300rpm 82 633csi

Post by BCMac » Thu Oct 15, 2020 11:35 pm

Hey folks, My very original 108k mile 1983 US-spec 633csi 5sp car has developed a most unusual behavior: With the engine revving between 3000-3300 rpm, a low, grumbly "wawawawa" sound is heard inside the cabin. The sound will occur weather the transmission is in neutral or in gear, stopped or underway, and does not seems to be driveline related. Engaging the clutch makes no difference in the sound. Engaging the AC compressor, turning the wheels right of left make no difference. The water pump is nearly new.

The sound is evident while standing over the right rear quadrant of the engine bay, and less so from underneath the car while aloft on a lift. The sound does not telegraph through the exhaust system - the cat seems to be fine with no rattles, and the heat shields are tight.. same with front and rear mufflers and their mounts.

My car's behavior mimics the subject of this 2007 post, but this post did not reach a definitive conclusion.

https://bigcoupe.com/phpBB2/viewtopic.p ... ion#p37070

To my ear, it sounds like something, somewhere, is making contact with the body of the car. I've looked high and low and cannot see where this could be happening. The RH engine mount is original an sagging. LH mount okay, as are the tranny mounts. I am beginning to think that the clutch has some kind of age/milage related flaw. Could be a pilot or T/O bearing, perhaps an input shaft bearing. In my experience, those parts make a much more consistent sound when they're failing.

Has anyone else experienced this low "wawawawa" sound in their E24?
BC MacGregor

'84 M635 euro Hans
'83 635 euro Frans (Sold)
'82 633csi US Fred the Fed

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clipper47
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Re: Mystery Vibration @ 3000-3300rpm 82 633csi

Post by clipper47 » Fri Oct 16, 2020 12:59 pm

Have you considered the fan clutch?
Dave
_____________
1985 635CSi US
Cosmos Blue/Pearl Beige

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BCMac
Posts: 36
Joined: Fri Apr 12, 2013 6:49 am
Location: Bellingham, WA

Re: Mystery Vibration @ 3000-3300rpm 82 633csi

Post by BCMac » Fri Oct 16, 2020 5:36 pm

I sure did. With the engine idling and a shop rag in hand, I stopped the fan and revved the engine to 3000rpm. The grumble did not abate.
BC MacGregor

'84 M635 euro Hans
'83 635 euro Frans (Sold)
'82 633csi US Fred the Fed

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clipper47
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Location: Ontario, Canada

Re: Mystery Vibration @ 3000-3300rpm 82 633csi

Post by clipper47 » Fri Oct 16, 2020 10:32 pm

Have you tried to use a stethoscope or a piece f rubber hose in the ear to try to isolate the sound ? Maybe a alternator of water pump bearing etc.?
Dave
_____________
1985 635CSi US
Cosmos Blue/Pearl Beige

Pod
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Re: Mystery Vibration @ 3000-3300rpm 82 633csi

Post by Pod » Mon Oct 19, 2020 11:30 am

Can you post a video with sound?

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