E220 Estate SLS THE DROP

[atlantimd]

Hi I have a S211 estate withs elf leveling suspension. It was dropping on the n/s rear and if left for a few days it fully dropped. The car has 156k so i decided to get aerosus rear bags. I fitted these and which went without issue. Now the car lowers over night by about 1" both sides. I have checked for leaks cant find anything using gas leak detector. I have checked the compressor which raises the car fine and shuts off ok. I will order a repair kit and inlet filter for a future job. I have Icarsoft MB2 the only fault i got was when i started the car with only 1 aerosus on the n/s, Once the 2 were fitted fault code cleared. Icarsoft shows the level of the raer changing.
So I am out of ideas now. Any ideas appreciated

 

[malcolm E53 AMG]

I think you need to refurb the compressor before looking elsewhere there is a possibility the system isn’t getting up to full pressure

 

[atlantimd]

Thanks for reply Malcolm. When the car is started the compressor lifts it within 20 seconds to correct level. I an just wondering can it leak back through the compressor. This morning it was only down 1/2" on n/s. I have trawled through all forums and from what I understand the Airvalves on the suspension units should stay closed over night.

 

[steveq]

Is the location where it is parked overnight completely level?
If there is a slight inclination the suspension will adjust to level out the rear.

 

[Janchee]

Common for pressure relief valve to stick and not close properly ie letting the air out

 

[MJJ]

Like you, I have just changed the rear bags to Bilstein on my facelift S211 (just rear air suspension, not airmatic), and learned that it really is a simple system. I would assume you have seen all the same things installing your new Aerosus bags.

Each airbag has an air inlet, with a one way valve inside the airbag - the compressor can fill the bag via that inlet, but air cannot be released, even if there is a leak elsewhere in the air lines or compressor valving.

Then, there is a pressure release valve on each bag with an electrical connector - 5v needs to be applied to the pins to let air out of the airbags.

The bags are not mechanically connected in any way together, so a leak in one will not affect the other (assuming the inlet one way valve is working correctly on each airbag).

So, in my opinion, the *only* ways for the system to drop on both sides would be:
- Two identically leaky airbags (hugely unlikely)
- The car's level sensor is telling the suspension control unit that the ride height is too high, and thus it releases pressure in both bags simultaneously.

As you have Carsoft, use the 'Live Data' function to view the car's ride height value and see if the car considers itself to be at zero when the suspension has dropped that inch. If so, and you cannot live with that, you will need to adjust the ride height sensor to re-zero the correct ride height.

Martin.

ps: One slight caveat to the above. I *think* it would be possible to install the airlines incorrectly in such a way that they protrude too far into the airbags, and thus always force the one way valve open. This would then cause the pressure to release, but I would expect the car to drop down on its bumpstops, not just an inch.

 

[atlantimd]

Hi Thanks for the reply. As for where the car is parked I would consider it level and have photos of the car a year ago sitting Norman in the same spot. This morning after 2 days the car is lover 1" O/S/R and down 2" N/S/R. I decided to start it up just incase it went too low and overwork compressor. It raised within 15 seconds. I will check the ride value tomorrow when its dropped. ( I Seem to remember it saying 6 mm with car Idling)
Regarding the airlines Martin I fitted the brass fitting and and ring with plastic insert into the New Airbag then removed insert and pushed airlines in as far as I could then nipped up the 10 mm fitting. Gas leak detecter stayed on them. The system looks very simple but it defies Logic previously it would fully drop n/s to bump stop and o/s followed a day later. This had happened once in 2017 on o/s parked in airport over 2 weeks. Now after new aerosus bags this seems to have differing symptoms.

 

[Janchee]

Washing up liquid in a bottle help? To try and find the leak? See where it’s bubbling

I don’t know about the pipes... see if you can isolate the compressor and see if it still goes down ie pinch the lines.

 

[MJJ]

Regarding the airlines Martin I fitted the brass fitting and and ring with plastic insert into the New Airbag then removed insert and pushed airlines in as far as I could then nipped up the 10 mm fitting.

I am no expert, but sharing this in case it helps you with your diagnosis. I think that this *might* be the problem. As I said in my last post, there is a one way valve on the airline inlet port - if the airbag contains air, and you push a thin screwdriver in to that inlet hole, you can push open the one way valve and the air releases back out of the inlet.

You would not design the airbag with a one way valve on the inlet *and* an electrically controlled pressure release valve unless you intended the one way valve to remain shut for the majority of the time.

Oh my amateurly edited picture below, and based on my measuring the bags I have recently taken off my car (yours may be different) if the protruding airline distance is more than 8-10mm and pushes in even further when the brass fitting is screwed in, then I think it will be opening that one way valve. Now, the brass fitting is airtight so it just means air releases back into the airline, and would leak from the car if there is a leak elsewhere in the valving/airlines.

On my car, I fitted the airline such that the protrusion was only 2mm, and thus the one way valve remains closed. The compressor is easily able to open the one way valve when it is pumping, but when it stops, the airbag is now a completely sealed system and it won't matter is there is a leak elsewhere in the system.

This is hardly proof of your issue unfortunately, but it might be worth letting the system pump up the bags, then unscrew and remove the airline brass fittings (thus ensuring the one way valves are closed) for a few days and see if it still drops.

Martin.

 

[atlantimd]

Thanks for the info. weather bad now but when it clears I will run the car to pump up the rears and unscrew the airline fitting to airbag and fit wheels and lower. Now the only problem I can foresee is that the computer could tell the bag to exhaust some air and It goes too low.
I did notice once when the Key was off position and after the car was let off the jack the electric valve opened and the car lowered slightly to the correct level "I could hear the click". The old and new airbags Have 1 electrical 2 pin connector and 1 Air connector ( Pressure release Air exhaust out Air connector when 5v Applied).
Hope your theory is correct as Its baffling me.

 

[atlantimd]

As you have Carsoft, use the 'Live Data' function to view the car's ride height value and see if the car considers itself to be at zero when the suspension has dropped that inch. If so, and you cannot live with that, you will need to adjust the ride height sensor to re-zero the correct ride height.

Car was low on passenger rear as usual about 2" and driver rear slight 1/2" possibly because other side pulling it down. I have live data before starting the engine and compressor. -15mm on the rear before being pumped up & 1mm after. Interestingly the Compressor and system is De-activated with Icarsoft in the suspension menu. Have not got around to checking are the pressure lines pushed to far into airbags ( Bad weather). I have a WIS copy of fitting airbag and it tell you to pull back pipe so it seat on the clamping copper ring.

 

[BigAlMercMan]

Following this thread with interest. My s211 started dropping ages ago. Fairly infrequently at first, now it's every time the cars parked, sometimes very quickly and other times a couple of days.

A boost issue prevented me using the car so I'd nearly written it off but with covid and having so much time on my hands I've started a bit of a refurb on the old girl. A new E is on the cards so trying to keep the cost down.

I've learned loads from this post, so many thanks for that. It's got me thinking if the one way valve is serviceable, if I can get to them and clean them up might I a have a cheap fix?

 

[MJJ]

It's got me thinking if the one way valve is serviceable, if I can get to them and clean them up might I a have a cheap fix?

The one way valve I am talking about above is an integral part of the airbag itself, and is not serviceable. If your suspension is dropping, tired and leaky airbags are by far the most probable cause. I think what happens is over time, age and wear produces a small leak - the car then tends to drop more when parked, making the leak worse, so you have a gradual but accelerating failure.

If you want your car to live a little longer, I would simply replace both airbags. I bought these Bilstein replacements for £234 each.

This Arnott Youtube video is excellent for showing the work required to replace them. The only complication I found doing mine, was that it is really important to inflate the new airbags before lowering the car down to the ground. The car will not automatically start the compressor until the ride height sensor shows the car as 20mm too low. You are supposed to use Star to inflate the bags, but I simply undid the two bolts holding the ride height sensor and manually manipulated it until the compressor kicked in and inflated the bags.

Martin.

 

[BigAlMercMan]

The one way valve I am talking about above is an integral part of the airbag itself, and is not serviceable. If your suspension is dropping, tired and leaky airbags are by far the most probable cause. I think what happens is over time, age and wear produces a small leak - the car then tends to drop more when parked, making the leak worse, so you have a gradual but accelerating failure.

If you want your car to live a little longer, I would simply replace both airbags. I bought these Bilstein replacements for £234 each.

This Arnott Youtube video is excellent for showing the work required to replace them. The only complication I found doing mine, was that it is really important to inflate the new airbags before lowering the car down to the ground. The car will not automatically start the compressor until the ride height sensor shows the car as 20mm too low. You are supposed to use Star to inflate the bags, but I simply undid the two bolts holding the ride height sensor and manually manipulated it until the compressor kicked in and inflated the bags.

Martin.

 

[BigAlMercMan]

Thanks Martin, You've answered something that's been on my mind for ages! They guy on the video makes it look sooo easy, I doubt it would go so smoothly for me on a 17 year old motor working on the drive, but nothing I can't handle hopefully.

I like the tip about manipulating the sensor, I've not located it yet bit I've got WIS so that won't be a problem.

I've got a part on the way to sort my running issues, if it works I think these may be next, but looking at the state of my air intake this won't be the end of my troubles.

Thanks again

Alastair

 

[steveq]

Another option is to put the wheel back on and lower the car on the jack carefully so that the wheel is on the ground and the rear of the car is slightly lower than the standard height (an inch or two lower) -- and then stop lowering the jack.
Start the engine - the height sensor will trigger the compressor to run and the new air suspension unit will inflate and raise the car off the jack.

 

[MJJ]

Another option is to put the wheel back on and lower the car on the jack carefully so that the wheel is on the ground and the rear of the car is slightly lower than the standard height (an inch or two lower) -- and then stop lowering the jack.
Start the engine - the height sensor will trigger the compressor to run and the new air suspension unit will inflate and raise the car off the jack.

I am sorry Steve, but I think this is a bad idea personally. All of the suspension airbag manufacturers go to great lengths in their online material, and printed instructions sent with the bags, to say 'do not do this, damage will occur and your airbag warranty will be void'.

This may well be backside covering by the suspension manufacturers, but the rear suspension is significantly compressed at the point where the compressor would kick in, and I do think it will significantly shorten the life of the new bags. The rear axle ride height sensor is easily accessed from under the car, de-mounted (two bolts), and manipulated to trigger the compressor. 10 minutes max work, and the engine does not even need to be on - just ignition position 2.

Martin.

 

[Mr Greedy]

Just as a reminder on this brilliant and detailed thread (thanks MJJ for super input) that the thing that often kills the airbag compressor is excessive duty cycles i.e. when you have a leak, the compressor is running every time you start the car. Sinking rear suspension iss not something to leave until later, as you could then end up replacing the airbags and also find the compressor needs attention.

 

[steveq]

I didn't say to lower the car until the suspension was 'significantly compressed'. I said tho lower it using the jack until it was slightly lower than normal height
- but absolutely not until it was fully down. The air bag would be just as compressed as it would be in normal use.

To be honest, I wrote that as I was trying to suggest a simple method of triggering the air suspension to activate without the need to be lying under the car at the time!! Personally, I don't like lying under the car with just axle stands holding it up at any time. I certainly wouldn't like doing it to start playing with the air suspension height. It would be far too easy to move the sensor the wrong way and trigger it to drop !!
Of course, I am assuming the work is being done as a DIY job on the driveway.

When I read the post above I watched a video of someone doing the job professionally as a demonstration. They had the car on a hoist, replaced the rear air bag.
Then he said that the suspension bolts should not be tightened up to the full torque until the suspension was at the normal ride height.
He proceeded to use a screw jack to move the suspension to the normal ride height with the car still on the hoist -- in doing so he compressed the air bag somewhat. He then tightened all the suspension bolts to the correct torque.
Then he put the wheel back on and lowered the hoist so that the wheel was on the ground but no weight was on the suspension.
He then started the car so that the air bag inflated.

 

[atlantimd]

I am no expert, but sharing this in case it helps you with your diagnosis. I think that this *might* be the problem. As I said in my last post, there is a one way valve on the airline inlet port - if the airbag contains air, and you push a thin screwdriver in to that inlet hole, you can push open the one way valve and the air releases back out of the inlet.

You would not design the airbag with a one way valve on the inlet *and* an electrically controlled pressure release valve unless you intended the one way valve to remain shut for the majority of the time.

Oh my amateurly edited picture below, and based on my measuring the bags I have recently taken off my car (yours may be different) if the protruding airline distance is more than 8-10mm and pushes in even further when the brass fitting is screwed in, then I think it will be opening that one way valve. Now, the brass fitting is airtight so it just means air releases back into the airline, and would leak from the car if there is a leak elsewhere in the valving/airlines.

On my car, I fitted the airline such that the protrusion was only 2mm, and thus the one way valve remains closed. The compressor is easily able to open the one way valve when it is pumping, but when it stops, the airbag is now a completely sealed system and it won't matter is there is a leak elsewhere in the system.

This is hardly proof of your issue unfortunately, but it might be worth letting the system pump up the bags, then unscrew and remove the airline brass fittings (thus ensuring the one way valves are closed) for a few days and see if it still drops.

Martin.
View attachment 66366

I got to have another look at the suspension today. I loosened the pressure fitting to the airbag I noticed that the pipe on the near side would slide in and out of the fitting approx 3mm so as Mercedes say in above document I pulled the pressure pipe back fully to seat the ring and tightened. I did get more turns tightening then before (But being careful as its mostly plastic). I sprayed leak detector and Soap and water and no leaks.
So I am going to see will it drop overnight. I don't think the pipe is pressing on a valve in the airbag and can't see evidence of a valve on the old airbags.
I will update tomorrow.