W212 Knocking from rear-Shocks?

[reflexboy]

My W212 has a knock when I go over bumps form the rear offside. Don't laugh, but I laid in the boot whilst a mate drove around and having pulled back the boot lining on that side, I'm convinced by putting my fingers on the side/top mounting bolts of the shock, it is the shock that is knocking.
Is this a common problem? The shock seems to be working as it should with no 'wobbling' when bounced up and down. Is the top mount separate to the shock or does it need to be replaced in one unit? Could it just be the mount that's knackered? Can this be bought separately? I presume if it's the shock, I will need to replace them as a pair? It would seem the top mount is available separately. Any idea how the top of the strut attaches to the top mount? Does it just bolt through? Is there a rubber bush that could be knackered causing the knocking? Any advice would be appreciated. Thank you

 

[reflexboy]

Anyone?

 

[grober]

It may simply be the shocker is "transmitting" the knock rather than causing it. The rear anti roll bar is connected to the suspension via drop links and these would be high on my list of possible suspects. Shockers that "knock" often leak fluid which is obvious on inspection.

this is from an E500 I believe. May be a bit beefier than the standard ones ??

 

[grober]

You might alternatively have a broken spring

 

[reflexboy]

It may simply be the shocker is "transmitting" the knock rather than causing it. The rear anti roll bar is connected to the suspension via drop links and these would be high on my list of possible suspects. Shockers that "knock" often leak fluid which is obvious on inspection. this is from an E500 I believe. May be a bit beefier than the standard ones ??

Thank you-I was wondering if it maybe the top
mount of the shock rather than the actual shock.

 

[reflexboy]

You might alternatively have a broken spring

I have had a look at the spring and it looks ok

 

[grober]

The top mount appears to take the form of inverted metal cup with 2 upward facing studs with the shocker piston rod embeded/fixed in some sort of elastomer block in the centre. The top of the shock has a flexible bump stop that appears to fit into the cup. The bottom end will be a circular ring/pin mount. I imagine it all comes as one piece ?? certainly not listed separately in the EPC.

 

[reflexboy]

Strange as having googled it, several places supply the top mount with the two studs. I'm now wondering how the top pin of the shock attaches to the top mount and whether that is loose or the rubber has gone back/split. I know the bolts on the end of the two studs are tight

 

[190]

No direct experience with your rear shocks but if they are "adaptive shocks" that use some internal mechanism to change the damping rate according to how the car is driven then they can fail in away that produces a knock. In my case it was a front shock on a W204. My symptoms were that the knock was most prevalent at low speed over rough ground. A new shock cured the problem.

 

[reflexboy]

I think I will remove the shock at the weekend and look at the state of the rubber and ensure the nut is tight at the top mount. I found this which may be needed: https://www.ebay.co.uk/itm/291771800870

 

[reflexboy]

Removed the shock and it seems fine. The bottom and top mount were in good condition with no excessive play in the rubbers and the strut compresses ok with good force and all nuts and bolts were tight . Think I'll get PCS to take a look as I'm due a service and MOT soon. Maybe it's nothing to do with the shock. Nothing obvious with the surrounding suspension components either, but then again I'm no expert.
Just drove it and it's 50-60 percent better. Weird eh?

 

[reflexboy]

Turns out it was the shock after all. Explained the symptoms to Jack and immediately he said it's most probably the shock. C's and E's suffer with shocks failing. He was spot on. So with that fixed, a fresh MOT with no advisories and an A service, I'm a happy boy thanks to PCS!!

 

[Lyserman]

I had a similar issue on my C32.
Worse when it had a rear passenger.
Changed everything else but the shock and still there.
They had to be from MB due to the AMG stamp, hence my reluctance to change the shocks.
Finally relented, new shocks and all quiet again.
The old shock didn't feel knackered when removed from the car, still smooth travel and damping. Just sounded like someone was hitting the rear floor with a hammer.

 

[Monkeylegend]

Had the same on my 212 and it was very slight play in the top mount, the shock itself was working properly.

Mercedes replaced both rears under warranty.

 

[reflexboy]

I had a similar issue on my C32. Worse when it had a rear passenger. Changed everything else but the shock and still there. They had to be from MB due to the AMG stamp, hence my reluctance to change the shocks. Finally relented, new shocks and all quiet again. The old shock didn't feel knackered when removed from the car, still smooth travel and damping. Just sounded like someone was hitting the rear floor with a hammer.

Yup,exactly the same here. My neighbour helped me remove the shock and we thought it seemed ok....wrong. I suppose experience and knowledge of the brand count for everything