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'Knocking' sound from rear

Discussion in 'E24 (1977-1989)' started by imacipc, Mar 16, 2014.

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    imacipc MI 633csi

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    So my '82 633csi recently started up with a sort of knocking or clicking sound coming from the rear. It is quite difficult to describe what it sounds like, but nothing big and harsh but just a loud and percussive almost metallic tapping sound from the rear of the car, almost like a parking brake twanging when backing up in the morning. The sound is external as you can here it from outside the vehicle, but also very loud on the interior of the car. This sound occurs mainly and most definitively when coming off the accelerator or depressing the clutch, anytime that power is being but to the rear wheels and then removed. The sound occurs in a short series of three or four 'knocks' but is quite loud and quite annoying. There does not seem to be any mechanical affects that can be felt like something in the brakes, steering, power delivery, etc. and is merely audible at this point. Previously during the same conditions there was a slight squeaking sound but this has since taken its place, not sure if there is any relation. I've looked underneath but can't visibly see anything but then again I'm not entirely sure what I'm looking for; I've also tried moving with the parking brake 2 notches up to see if it may need readjusting but it made no difference. If anybody has any suggestions on what to check for that would be great!
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    charlson89

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    This could be many things hard to say without hearing the noise. Is there any way you can get a video of this?
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    imacipc MI 633csi

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    MGarrison

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    If you have the noise largely isolated to the upper deck corner like that, my guess would be your shock mount's given up the ghost and now your shock is hitting the car when the suspension compresses & is rattling around up there. If it was lower or less specific spot-identifiable, I'd say maybe something like subframe or trailing arm bushings, or swaybar or swaybar link bushings but my guess is sounds like shock mounts or something related to that area.
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    charlson89

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    Well it sounds to be suspension related could be sway bar bushings, control arm bushings. The quick way to diag is to use a stetha scope a listen to different areas and the area that is the loudest is probably the issue. The other way to diag is to spay those mentioned bushings with WD-40 and the noise will decrease when you find whats causing it. Hope that helps.
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    imacipc MI 633csi

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    Thank you so much for your help!
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    imacipc MI 633csi

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    charlson89

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    I'm not seeing anything to crazy on those pictures. It looks like the Right rear dust boot has come up a little on the strut thats nothing to be worried about.
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    imacipc MI 633csi

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    That's great to know thank you. All of the other bushings you mentioned seemed to look fine to me so I will continue to try to isolate the source. Once again thank you so much for your help!
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    MGarrison

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    If you have an inspection mirror, that might be a way to get a view direct up at the bottom-side of the shock mounts. To get a look at them from the top side _probably_ means pulling the rear seat bottom and seat back, at a minimum. I wouldn't know what the bottom of your shock mounts are supposed to look like offhand, but, on your picture of the left rear, the tapered part at the top that looks rusty, I'm wondering if that's solid or squishy (& if your picture is with the car jacked up or if that's with the wheels on the ground) - if it's squishy, that might be the rubber center section of a shock mount that's separated from the rest of the shock mount. Jacking up each rear corner and observing if anything looks amiss might be one thing to check, if your pics are with the suspension compressed & wheels on the ground instead of jacked up at full droop.

    http://www.harborfreight.com/telescoping-mirror-7361.html

    Here's an E24 site: http://www.bigcoupe.com/

    E28's are similar vintage, tons of experience over there, search those forums & perhaps pose a question if you don't find anything: http://www.mye28.com/

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