Mystery Vibration @ 3000-3300rpm 82 633csi

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BCMac
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Location: Bellingham, WA

Mystery Vibration @ 3000-3300rpm 82 633csi

Post by BCMac »

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

'82 633csi US
'84 M635 euro (Sold)
'83 635 euro (Sold)
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clipper47
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Re: Mystery Vibration @ 3000-3300rpm 82 633csi

Post by clipper47 »

Have you considered the fan clutch?
Dave
_____________
1985 635CSi US
Cosmos Blue/Pearl Beige
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BCMac
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Location: Bellingham, WA

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

Post by BCMac »

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

'82 633csi US
'84 M635 euro (Sold)
'83 635 euro (Sold)
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clipper47
Posts: 596
Joined: Mon Oct 10, 2011 12:22 am
Location: Ontario, Canada

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

Post by clipper47 »

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 »

Can you post a video with sound?
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BCMac
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Location: Bellingham, WA

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

Post by BCMac »

I've had the 633csi out for the past couple of days and was once again vexed by the mystery vibration between 3000 and 3300rpm.

This afternoon, I replaced a partially collapsed RH engine mount, which brought the engine back to proper position but of course did nothing to alleviate the noise. ](*,)

With renewed determination, I stood over the right side of the engine bay and operated the throttle with my left hand: This time, I was able to detect the vibration in the RH strut tower courtesy the AC line mountings there - and ultimately to the compressor. It vibrated in time to the WAWAWA noise at 3000-3300rpm. This in turn was caused by a missing M8 bolt on the engine side of the AC compressor's adjusting bracket. The bracket could be seen to (barely) move independently of its mount on the engine during the vibration. A replacement bolt was installed and the engine revved: No more vibration! Spent more time at 3000rpm than necessary on the drive home from the shop, simply because I could! Victory!! \:D/ :D :mrgreen:

Time to add some more miles to that lovely Chestnut Red Metallic / Kastanienrot E24!
BC MacGregor

'82 633csi US
'84 M635 euro (Sold)
'83 635 euro (Sold)
Pod
Platinum Member
Platinum Member
Posts: 4492
Joined: Tue Mar 16, 2010 8:32 pm
Location: usually in the barn, Kent, England.

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

Post by Pod »

Pleased to hear you tracked the problem down after so long. Thanks for sharing 😉
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