Advice requested - how to actually test a leaking suspension airbag?

[MJJ]

Hi all,

I suspect a leak in the N/S rear airbag of my '09 S211 - quite a small one I think as it does take a good 5+ days for the suspension to drop. No dash warnings, and the compressor happily restores ride height when the engine is started. Car has rear air only (not Airmatic) and has 180k miles on it so I am doubting the bags are original.

I want to confirm a leak before simply replacing the pair, but am struggling to find a way to do that effectively. Car is on axle stands with the rear wheels removed, thus the suspension is at full extension and under no load. Additionally, the airbags currently fitted appear to have a rubber gaiter over the actual spring bag, so soapy water is just testing the gaiter. I don't think the bags are OEM as the part numbers on the bags don't tally with anything Mercedes part number wise in EPC.

Any recommendations or tips? Do the bags need removing from the car, inflating somehow (I have a compressor), then put into a large bucket of water to test?

Also, any recommendations for replacement? I am tempted to choose Arnott, but will see how much the OEM part is first.

Thanks,

Martin.

If it matters, these are the bags fitted to the car. Part number EK781606M/R815006000 only tallies with used parts on a Google search.

 

[plastic]

Hi Martin

I too have a 2009 S211 220 CDI (not airmatic) with 160k miles on it which within the past 3 months has started sagging on the NSR corner when left for anywhere between 2 and 5 days. Weirdly it sinks overnight, guaranteed, when there is < 1/4 tank of fuel in it, but takes longer (several days) when there's more in it - must be related to the pressure the bags are at with extra weight in the back.

I see from your messages that you replaced yours with Bilstein bags. I am making an assumption that my bags are past their best as I believe they are probably the originals (had the car since 80k miles). Did this cure your problem? I am making a huge assumption that our cars are equal, though given the age and mileage maybe that isn't too ridiculous.

Currently, also, when pumped up my NSR is also maybe 10-15mm lower than the OSR - was this true of yours?

Cheers

 

[MJJ]

Hi @plastic ,

Your symptoms sound identical to mine, although I never went to the trouble of measuring ride height side to side when the suspension was fully inflated. I would say that on mine, both before and after airbag replacement, the side to side ride height can often look slightly uneven depending on what surface you have parked on, what is in the boot already, and even if the car was still slightly moving when the parking brake is applied. From my post airbag replacement testing, the compressor only kicks in if the car sees the ride height as 20mm or more below where it should be - that suggests it is entirely normal for there to be slight differences. Compounding this is the fact that there is only one ride height sensor on the back axle, there is no way for the car to know individual left and right ride heights.

I have had the Bilsteins on for about a month, and 500 miles or so now - including a fair bit of towing a very heavy trailer. I am confident my problem is solved.

Martin.

 

[AW8]

MJJ

S212 owner here ( air to rear only....not air-matic )

My understanding is that it is difficult to accurately diagnose or pin point a bag air leak. As you have rightly pointed out the bags are encased in gaitors.

I took mine to an indy to diagnose using proper MB spec diagnostic kit for ride height etc.......the best I got was an educated and informed opinion it was most likely a leaking bag with the best advice to replace both bag.s

Prior to my ownership last keeper told me main dealer could not diagnose fault or identify leak source.....

I since had them swapped out to Arnotts x 2....no issues since

 

[plastic]

@MJJ & @AW8

I have read elsewhere that as you have suggested these systems aren't actually that complicated - as you say there is only one ride height sensor so both bags are pumped up to the same pressure (ideally) individually. At least they're only on the rear!

I'll look to getting the Bilsteins as they seem to be a good price.

Cheers both