W220 S320 CDI VERY HARD airmatic suspension - Ideas Please?!

markben

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Dear w220 S Class owners / techies

Can anyone help with a continuing problem with harsh suspension / ride on my pristine but very 'lumpy' 2004 S320L CDI! Mileage 112k, airmatic compressor & relay replaced at approx 70k, no airmatic leaks, front strut tops appear perfect (no cracks) car always maintains height / no 'dropping' when left for a few days. 3 lots of STAR diagnostics have shown-up NO airmatic faults other than a front accelerometer - which was replaced with no improvement - and the struts reported 'to be actuating ok'. No warning lights coming on, car raises as it should using the dash button. Tyres / pressures all checked (Continental Conti Eco contact 5 XL). Lots of front bushing / control arms / ball joints replaced along the way. Very thorough service and maintenance history - cherished by previous owner.

BUT...! The car rides atrociously (i.e. extremely stiff / harsh damping) over even small depressions and ridges on urban roads - almost as if the airmatic sytem pressure is too high / not releasing or adjusting to enable effective 'soft' damping, especially at the front? It rides more like a go kart!

Could this be down to a faulty / 'sticky' valve block and / or pressure release valve - but which isn't showing up on STAR when the car is stationary (only a guess)? The harshness seems to vary a little at times but is never 'butter soft', as one member described it should be like. The car was unused for several months before I bought it. In all other respects, it's superb.

Any ideas much appreciated...

Many thanks

Markben
 

John Laidlaw

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I know you’ve covered tyre pressures ‘Tyre pressures checked’ but the recommended pressures are invariably too high for a ‘limo’ like ride. I’d start there, drop a few psi out and see what it feels like. Hopefully a super cheap fix. Anything else should have been taken care of with the repairs which have been done.
Interested in the description ‘Struts actuating ok’ - was there more detail at all?
 

AMGeed

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Assuming you have the damping at the softest setting I'd blame to atrocious condition of our roads.

My airmatic doesn't give the softest of rides but that is always in sport setting.
 

malcolm210

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Start with tyre type, load index and wheel diameter, if updated to 19/20in this will make difference as will pressures

As AMGeed mine stays in sport all the time comfort being too soft for me but mine rides on 18in and fairly pleased with the handling and if anything a fraction on the soft side for me but with our roads kinder on the alloys

Might be worth posting tyre type load index and size for a better opinion
 

John Laidlaw

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Yip should have said, as the others, mine sits in a sports setting (there are effectively 3) on 19in wheels and no, you couldn’t say it was magic carpet like either
 
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markben

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I know you’ve covered tyre pressures ‘Tyre pressures checked’ but the recommended pressures are invariably too high for a ‘limo’ like ride. I’d start there, drop a few psi out and see what it feels like. Hopefully a super cheap fix. Anything else should have been taken care of with the repairs which have been done.
Interested in the description ‘Struts actuating ok’ - was there more detail at all?

Thanks John, tyres are Conti Eco contact 5 101W rated XL on standard OE MB 17" twin spoke alloy rims, Front 29psi / Rear 30psi as recommended by manufacturer. I check them every week but will try lower pressures as you suggest. As for 'struts actuating' - this was the comment from an ex MB techie (now Indie) who did STAR on it - but when stationary. No other qualification, just seemed to suggest that the struts are ok..
 
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markben

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Start with tyre type, load index and wheel diameter, if updated to 19/20in this will make difference as will pressures

As AMGeed mine stays in sport all the time comfort being too soft for me but mine rides on 18in and fairly pleased with the handling and if anything a fraction on the soft side for me but with our roads kinder on the alloys

Might be worth posting tyre type load index and size for a better opinion

Thanks Malcolm, I've posted tyre / rim details in my response to John... BTW, Sport 1/2 settings don't seem to make any noticeable difference, the car behaves better ride-wise on motorways but still feels a little stiff over ruts, ridges etc even in Convenience setting...
 
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markben

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Assuming you have the damping at the softest setting I'd blame to atrocious condition of our roads.

My airmatic doesn't give the softest of rides but that is always in sport setting.

Ha, AMGeed! :) Well the road conditions don't help but I swear that even my old W210 E55AMG Estate had a softer ride! Yep, I always use 'Convenience' setting.
 

malcolm210

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I’m amazed the ride should be sublime with 17in alloys standard tyres and pressures you stated, definitely something amiss it may be a sticking valve block judging by your comments in #1
 
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markben

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I’m amazed the ride should be sublime with 17in alloys standard tyres and pressures you stated, definitely something amiss it may be a sticking valve block judging by your comments in #1

Thanks Malcolm, that was my best guess. I'm just curious that STAR didn't pick it up - maybe because a dodgy / sticking valve block won't show any faults when stationary, only when on the move? Any ideas if STAR can be used when the car is being driven..?
 
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markben

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I've never used it, but any diagnostic kit needs to be able to used on the move so it can collect 'live data'

Thanks EmilysDad. That's what I thought.. I'm just amazed that 3 separate Indies didn't recommend that - despite 2 of them briefly driving the car themselves and concluding that the airmatic suspension is 'ok'. But it will seem so when stationery or on smooth roads..!
 
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markben

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ANY diagnostic kit is only as good as the person using it ;)

Ah ha... of course! :-D I do wonder if some techies rely too much on diagnostic kit and don't look for other clues, especially with airmatic. But airmatic does seem notoriously complex.... Oh well!
 

John Laidlaw

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Ah ha... of course! :-D I do wonder if some techies rely too much on diagnostic kit and don't look for other clues, especially with airmatic. But airmatic does seem notoriously complex.... Oh well!
If you think Airmatic is complex......3 letters for you A. B. C. :D
 

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is it supposed to run on 101 load rated tyres I doubt it and then stiffer again at XL

on a 221 17" and 18" wheels are supposed to run 99 load index and don't go above 32psi
 

Paul1948

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Why are you running on heavy duty reinforced tyres, the recommendation is 98 not 101 XL which are for people carriers, mine runs on RS3 and 28 frony 30 rear for a fully loaded car, no hashle with any of the suspension setting or speed even continetal speeds.
 
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markben

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is it supposed to run on 101 load rated tyres I doubt it and then stiffer again at XL

on a 221 17" and 18" wheels are supposed to run 99 load index and don't go above 32psi

Good point Botus - the 101 /XL tyres were on the car when I bought it. I agree, probably not necessary and would certainly make the ride stiffer. Thanks :)
 
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