Hey friends, I have a 2005 S55 AMG W220 model Mercedes I bought last October. It has the Active Body Control suspension system and for the last couple months it's been sagging on the left front and rear wheels.

I have read that when a corner sags when parked on this suspension system it's usually an indication that either a Valve Block is failing or one of the Suspension Struts is leaking.

I suspect it is the Valve Blocks as I haven't noticed any spilled fluids on the garage floor and I check the ABC fluid levels daily and don't notice any drop in the level (I alternate between checking it while the car is running and while the car is off since there is a notch for each state on the dip stick).

One strange thing I realized is that there is a Valve Block for the front axle and rear axle, however my car has the left side sagging on both the front and the rear which seems odd since they are running off different Valve Blocks so it must be a coincidence that the left side is failing on both the front and rear Valve Blocks.

Another strange thing I noticed is that the amount of sagging over time is proportional to the temperature the car is sitting in. I have the misfortune of living in Ohio and our bi-polar weather has been flipping between sub-freezing temperatures or a balmy 50-60F for the last 2-3 months so I have been able to observe how the temperature affects the level of sag. In warmer temperatures such as 50F+ you might only observe 2-3 inches of sag if you let the car sit for the weekend. However when it get's below freezing the left side of the car will drop to the wheel wells in a couple hours. I have no idea what the implication of this is. Both the front and rear wheel on the left side seem to sag at the same rate.

Another piece of information I can give that may help is right after I bought the car I had the front accumulator and the ABC System Hydraulic Pump replaced, the ABC System Filter replaced and the ABC Hydraulic fluid changed.


Right now I'm considering trying to clean up the Valve Block as I've read that when they fail you can usually fix them by cleaning out the gunk build-up and debris and replacing all the O-Rings (keeping in mind I have to find some O-Rings that won't dissolve in hydraulic fluid). I'd hate to buy a new Valve Block as since the front and rear left wheels are sagging that means replacing both the front and rear Valve Blocks which are $2000 a piece. It would such to have to spend 33% the value of the car to fix a suspension glitch but I suppose that is what I get for such a risky automotive purchase.

I was wondering if any of the kind knowledgeable people who frequent this forum would have any suggestions or insight as to if I'm understanding/diagnosing my problem correctly and if the method I've chosen for an attempted fix is the right way to go. Thanks for any help provided, I really appreciate it.

 

Isolation valves in the valve blocks. Just coincidence that it is front and rear on the same side.

Make sure your fluid is clean but it sounds like it was recently replaced. If the fluid is indeed clean and new, personally, I would leave the control valves in place and just remove the isolation valves to redo the o-rings.

Remember to support the wheels when you take out the isolation valves. Do not let them hang on their own weight. You can also access the front isolation valves by taking out the headlight and reaching down in. It can save a little time but the valves can also be stuck in there pretty good.

 

Thanks for the information, that makes a lot of sense.

I don't suppose you would know where to purchase the correct O-Rings for the job?

I was going to go off the specs listed on this very helpful ABC Suspension troubleshooting guide and was looking at www.mcmaster.com for where to purchase.

 

I rebuilt my front valve body about 40k ago with O-Rings bought from Harborfreight....havent had any issues since then...

 

Welcome, Sean

If you haven't already done this, check out the very informative collection of ABC posts that Welwynnick has made.

Also Hoaz posts about ABC maintenance and general maintenance for his S600 are great primers for any S220 owner.

There is also a sub forum for AMG vehicles when you start getting into supercharger and M113K engine issues.