S211 Semi-Active - Rear Damper Replacement?

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E55BOF

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On my 2003 Airmatic S211, I've noticed that when the left rear wheel drops into a pothole the thump is noticeably louder than when the right rear does so. It doesn't happen at any other time.

It's not the rear subframe bushes; they've just been done. I'm inclined to suspect it's the damper on that corner. Does anybody have any other ideas?

(If it is the damper, it looks to be a piece of weewee to replace - boot trim out, undo top nut, undo electrical connector, jack up, wheel off, lower control arm shield off, undo bottom bolt, and out it comes. Even I, older and much creakier than I used to be, can still do that more-or-less in my sleep. Unless MB are cheaper than I expect (haven't asked yet) I'd replace with a Bilstein - there are much cheaper replacements from China, but, well, you know...).

If it does have to be replaced, will it need calibrating with a Star afterwards?
 
Does your car have anti roll bar links?

Presumably the shock absorbers will be replaced as a pair?
 
The car was checked over at Wayne Gates when I first got it, so it won't be anything as obvious as bushes.

MB specify that Airmatic shockers can be replaced separately; only the steel-sprung cars have to have them done as a pair.
 
I think the shocks would need to be replaced as a pair, the air springs would be ok individually. WIS does state normal shocks can be replaced singly up to a certain mileage IIRC 80k kilometres.
Are the shocks original? Perhaps just the mounting bushes need replacing?
Regarding STAR, good practice to reset the ride height and zero the mid-point.
 
I'm working from here:


which specifies that the non-Airmatic rear shocks must be replaced as a pair, but makes no such stipulation for the Airmatic units. I presume they took their information from WIS/EPC.

I've no idea whether the rear shocks are the originals, but they could well be; basic routine servicing had been done, though not often by a dealer or specialist, but the non-routine stuff - engine mountings, brake pipes, subframe bushes, ARB bushes, front suspension ball joints - had not.
 
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I'd start with the top mounts?
 
It's going in to Terry Gates on Monday for engine and gearbox service, so I'll get it looked at then.
 
Well, Terry's opinion was that it's the damper, so I'll change it. £450 from MB, £350 from Bilstein, but I got lucky; there was a place in Sicily with a N.O.S. OE one for £307. Result. If they'd had a right-hand one, I'd have bought that too. The damper plays no part in the ride height setting so far as I know, just cushions the movement when it changes, so nothing should need resetting.

I do hope the bottom mounting bolt isn't seized in place. MB nuts and bolts seem to resist corrosion pretty well, but it's probably the original after seventeen years... Has anybody done the job, and if so, was it seized?
 
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