Hello to all, looking for some advice from the Master General Lord King Boofoo of Airmatic .
Here are the details:
2010 S550 4matic
Overnight driver's front shock has been sinking at a slow rate. Comes right back up in the morning when I start it and drive through the day without any issues or warning lights. Had put in two new front Arnott shocks last year so didn't suspect them, but wanted to test anyway. I isolated them with separate lines and shut off valves and tested them for a day with no leakage on either side. Then I wanted to test the line going from the air block to the shock so I ran a new line and I'm still getting a leak overnight so I'm assuming that ruled out a bad line. BTW, passenger side goes down as well but not as much or all the way as the driver's side does, I've been told it will automatically go down to compensate for the weight distribution, don't know if that's true. Finally, I removed the supply line from the compressor that leads to the valve block and put it in water and I am definitely getting bubbles so I know the air block is leaking back somehow, not sure if it's supposed to do that at any point in time(car was not running), ie if the car is still awake or not completely locked up. Don't know if I'm testing that correctly, maybe should be waiting a certain amount of time after ignition turned off etc.
Anyway I'm thinking the valve block is bad because in my hours of research I kind of remember reading that there should be no air coming back through that line. I have no problem spending the money, but don't like just throwing parts at a repair without a fair amount of diagnosis. And of course, I sprayed down the entire system that I could get to at the Valve block, compressor, and shock towers and visible lines with soapy water, not seeing any bubbles or leaks.
Any other testing I can do( not sure if the level sensors or compressor could be of suspect for this situation), or If the consensus from all the Master General experts here is the valve block, would you go for any of the less expensive ones on Amazon or go straight for an Arnott or Mercedes.
Thanks for everyone's help in advance!
Adam

 

from what I read if the shock is right, and the line is right, then its either a connection with and or the block is playing up - (but I don't see how you know the pipe is OK from your description) - never fiddled with the valve block but they aren't silly money I believe, and if it has an electronics inside it could well be faulty (it's a Mercedes after all). Some people do swap the valve block and feel better about life

If you have a leak you will be putting more wear / usage on the pump - which is likely toward end of life - as they don't last long (as they often have more leaks than they should, but few notice). If you (allegedly) want to save money there are plenty of airmatic checks and tests built into dealer tools that should help you understand what to replace

they do need regular lube / testing and or replacement of the 3 level sensors, one each at the front, one hidden above and near to the left driveshaft (but that won't be why it drops - well not until they snap off)
they do needlessly morph to try and level when the key in on and the car is stationary - I guess to help wear itself out
the left rear is known to sag on early ones as they were so well made they damaged the pipe building the car
they do breath due to temp and atmospheric conditions when parked - with up to 20mm being quite a normal sag if its particularly cold overnight

 

Good job. This should help when you're ready to fix your problem.

 

if you spent 10 mins taking the pump off from beneath, the valve block is a lot easier to reach than madness this guy goes to

 

Do you have WIS? Approx $20 on eBay.

 

Suspension consists of two items … springs and shock absorbers.

On Airmatic equipped cars, the springs are rubber air bags. Shock absorbers remain hydraulic units, same as in vehicles with steel springs.

if your suspension collapses, it’s a leak in the air spring or its connecting plumbing. Shock absorbers do NOT collapse.

when shock absorber and spring are combined into a single unit, that unit is called a strut.

Your problem is easy to diagnose … Arnott.

 

You have done perfect troubleshooting already and found your problem. The only very small possibility could be that the valve control module is feeding low voltage in the valves in the block that is high enough to keep the valves cracked just slightly open and let air out. Well, I don't think this is happening...

Your valve block has gone bad or more precisely the valve for the driver's front in the block has gone bad and leaks. Passenger front goes down as the car body is stiff and won't twist so it has to go down with the driver's side.

Passenger side front goes down less as there is force in the one spring to keep car up and for this reason the passenger side rear is up some compared to driver side rear again due to the stiffness of the car body.

Replace valve block and you are good to go. The valve itself is an electro mechanical device (solenoid valve) and over time the valves wear and start leaking. I replaced mine when the car was about 10 years old. It was not leaking yet but at that age I thought it is not waste of money to replace it.

 

Thank you all for your help! Looks like the consensus is the valve block which I kind of thought but I'm happy to hear my thinking was going in the right direction. Any thoughts on which brand or a seller on eBay or Amazon to get from?? Big variation in price from off brands to original Mercedes, and they all seem to look absolutely identical. Once again thank you all for your help.

 

Arnott valve block if it's cheaper. Otherwise, I would consider the valve block a critical component and wouldn't hesitate on coughing up the dough on a factory unit.

I'm the kind of guy that would toss the old one on a bench first and try to tear it apart and fix it myself though. It's just nuts and bolts.

 

Sorry forgot to mention in my earlier post this part I replaced was for my E-Class. I did not hesitate to get MB part from my dealer ($350) but now I would try if FCP Euro has it. They sell OEM parts for less but I don't know if this part is in their selection.