Thumping sound from back on uneven road surfaces - Mercedes-Benz Forum
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post #1 of 19 (permalink) Old 08-15-2017, 01:12 PM Thread Starter
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Thumping sound from back on uneven road surfaces

My 83 380SL runs pretty quiet overall with no noticeable suspension rattles but when I drive over an uneven road surface, like two uneven concrete slaps, I get this fairly loud thump. When I remove the hard top the sound looks to be gone, but I am not sure whether that has to do with the enclosed space amplifying it or if the noise is coming from the hard top. The hard top seems to sit well but I went ahead and renewed the seal. The fit is tighter now, but not really making much of a difference in the thumping noise. The ceiling etc looks firm and I cannot see anything moving in particular.

Possibly related, when I close the boot (trunk) there is 'cheap sounding' clang, which I traced back to the sheet metal being loose from the frame. There is no insulation matting at the underside (should there be?) and I am considering to 'glue' the sheetmetal to the frame using a suitable mastic, if anything to make the closing sound more 'sophisticated' thud.

Has anybody found that fixing the boot helps reduce any road noises like the thumping described or am I completely on the wrong track and should be looking at suspension rubbers/dampers/etc?
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post #2 of 19 (permalink) Old 08-15-2017, 01:20 PM
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Forum member Rowdie diagnosed the rattling with my 1983 380SL - rear sway bar links - see photos.

Crawl under your 380SL and look on the upper inside of each rear wheel to see if these have broken loose and causing the rattle.
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"You have chosen to drive a MERCEDES-BENZ, a car in whose construction and production we have taken great pains because we believe that quality is not a matter of chance." -- page 3, Owners Manual 380SL
Timing Chain, Subframe, wiring harness, Climate Control, Rust prevention, etc.
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post #3 of 19 (permalink) Old 08-15-2017, 01:42 PM
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Sway bar links are a common cause of rear end noise and should be checked regularly. However, when failed they will cause all kinds of slop in the rear end, especially around turns, wheels scraping and all that. A broken link can slap around.

I've experienced a knock from a bad shock on my 280sl.

But if you think it sounds like sheet metal from the trunk, then maybe that's exactly what it is. You can place foam between the trunk frame and the metal to eliminate that sound. You could test it with a rag if no soft foam is handy.


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post #4 of 19 (permalink) Old 05-09-2019, 10:01 AM
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I have what seems like the exact issue JS5D described up above, with our '81 380SL. However, I do not even suspect sway bar links or deck lid. This (he calls it thumping) banging is definitely coming from the hard-top roof. And, like JS5D indicates, I can see no issues with how the top is mounted and latched-down. This began immediately after my mechanic replaced the front hardtop seal. The new seal is great and doesn't leak or anything - - 'just this rough-road banging of the roof. I did a LOT of searching here on the forum and this is the only thread I found that even began to address the issue. 'Any other ideas out there? TIA Don
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post #5 of 19 (permalink) Old 05-09-2019, 11:53 AM Thread Starter
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Hello. For an update, I have not yet found the cause, but suspect what it is the weight of the hard top and some flexibility in the mounting/seals. When I release the rear stud type clamp (rotate the lever on the side) the rear comes up a little and thumping goes away. My theory is now that the thumping is the hard top moving down (dt weight and compression of the seal) then it jumps up and it is the securing stud stopping the upward motion that makes the noise (or at least that is the theory).

What I was going to do is fit a rubber washer (like a shim) at the base of the mounting stud to give it less travel. Have not had time to try this as I have not removed the yardtop lately.
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post #6 of 19 (permalink) Old 05-09-2019, 12:37 PM
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Thanks, JS5D - - - 'seems to me like the rear side locks would prevent what you are suggesting. But, that certainly gives us something else to look at. Don
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post #7 of 19 (permalink) Old 05-09-2019, 12:50 PM
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Is the rubber grommet missing on yours?
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post #8 of 19 (permalink) Old 05-09-2019, 01:05 PM
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Now, something like that is EXACTLY what I was thinking about. I don't know as I haven't yet removed the hardtop for the season. I am guessing that might be the case - - maybe it was brittle/cracked and fell off when the new front seal/weatherstrip was installed and it wasn't noticed. If anyone might have a picture and a part number for that, it sure would be a great help in knowing what to look for and what to get . . . . Thanks! Don
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post #9 of 19 (permalink) Old 05-09-2019, 01:36 PM
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I will see if I can get a pic.
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post #10 of 19 (permalink) Old 05-09-2019, 01:38 PM
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GREATLY appreciated!
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