Rear suspension knock - top mount?
 

I'm trying to pinpoint a low-speed dull knocking sound that I can hear, but it's got me stumped.

I've had all of the rear axel components given a twice over on a ramp with a pry bar and two separate techs, but they can't find anything.

My gut instinct is that it feels like a sound coming from the upper strut area, ie where there would be a top mount, but upon calling my local dealer the guy told me that there isn't a top mount on my car and I would need to buy an entire strut, if that proves to be the issue. However, typing my model into various online parts stores, I'm able to find lots of top mounts of the same design but made by all of the usual suspects (Febi, Meyle etc) and they're supposedly for the W212 (although the part pre-fix starts with 204).

Anyone able to shed any light on this? Car is on 96k now..

Could be expensive to go with "gut instinct" and replace entire strut only to discover this not the source of the noise. Would be worth trying a good suspension shop for yet another opinion if you go down this route. The sound could still be be from all sorts of non suspension related components eg diff mounts, something loose in the boot eg power blind or motor for the boot close gear under the parcel shelf, even a loose rear passenger door hinge causing the door to "bounce" on the striker.
You might be as well off using the dealer to at least diagnose the problem and get a quote. They might charge you an hour's labour but this a lot cheaper than replacing something on spec.

Just had inspection done at MB and they're very complimentary of the underside of the car...all bushings, arms and suspension appear intact and healthy.

The mystery continues.

I'm going to pull the struts at home this weekend and then visually inspect the top mounts. I've found a supplier that can sell me the top mounts, even though MB say they come as pat of the strut. I'll update on my findings.

So the MB tech's told me it's more than likely to be the top mounts. The car was serviced last week and I asked them to poke around. They were able to validate that all bushings, arms, springs and struts were fine.

I've ordered a pair of Febi Bilstein top mounts and they'll be fitted soon after they arrive next week. I'll update this thread in due course.

So this weekend I was able to remove the struts and inspect the top mounts. They looked a little worn with the rubber, so I replaced it with the Febi replacements that I had ordered. I replaced one on Saturday then went out in the evening, then replaced the other yesterday. After having just one replaced, it's hard to say if it has helped with the sound. The car felt a little nicer on turn-in on one side but the noise was still there, albeit I think i was only coming from the side that I hadn't replaced.....either that or there was a lot of placebo going on. I haven't driven the car since replacing the other side yesterday, but when I do, I'm not sure if the noise will be gone...the top mount didn't look like it had all that much play in it. The strut seemed fine. Next thing to check will be the airbag ffs.... here are some pics FWIW. Pay attention to the small rectangular rubber blocks on the side profile pics....the new ones are raised n fresh...the old ones are sunken in and that's where I might have been hearing the sound from...fingers crossed the noise is gone the next time i drive it.


https://cimg5.ibsrv.net/gimg/www.mbw...c366355d20.jpg
https://cimg6.ibsrv.net/gimg/www.mbw...705c38a72d.jpg
https://cimg8.ibsrv.net/gimg/www.mbw...06331d1045.jpg

https://cimg1.ibsrv.net/gimg/www.mbw...c286adfa34.jpg
https://cimg2.ibsrv.net/gimg/www.mbw...0d5da6eb68.jpg

Hi
Did the noise gone or was due to bad shock absorber?
I'm in the same position.
Thanks
John

Funnily enough in the end it was simply one of the sway bar links. Apparently it was slightly loose and enough to have play when under the cars weight, but not loose enough to be found with a pry bar on a ramp 😄

so simple. And it drove me crazy for so long.

Thanks for your reply,
I'll have to check as well with car's weight on.
Glad you sorted yours!

Question for you, sitting at 94k with a wagon myself, the top mount replacement, was it a noticeable difference for a sustained period of time? I can tell my car is a bit mushy, even for an e class.