sexyxe

To me that seems unusual that the distribution valve would cause rears to deflate. The bags hold air, they release it on electrical signal. The distribution valve at the front of the car would cause the bags to inflate slowly or not at all.

Glad it's sorted though.

MJBelcher500

I would have thought the same thing, but even after replacing the air springs it would still drop at the rear after a few days. There must be a mode where the bags are open to the valve at rest and there was a slow leak at the valve. Otherwise, it could have been excess water in the system from old desiccant in the pump. That might lead to higher pressures when hot and as the springs cooled the pressure dropped more than normal. Not really sure.

In any case, I feel better knowing all the parts in the system have been replaced.

Yuille36

If you have never swapped out your original air compressor, or had your compressor filter changed, you could have moisture build up within the compressor or valve block, thereby causing corrosion inside the valve block that has caused your seals to leak.
Changing out the valve block is cheap insurance, and doesn't cost a lot to do. Barring bad air-struts or air-springs, could be the culprit to a sagging issue.

MJBelcher500

Yullie, I had changed the filter, but the pump was original. I also replaced the intake hose as it was looking pretty sad.

My understanding was that at rest the air springs closed their valves and should not have pressure in the lines. If that is true, then the valve block shouldn't have fixed the issue. Do you know if when the car is switch off the air spring valves are open to allow pressure in the lines to the block?

Yuille36

I have been told by a reliable Mercedes technician, that some air is release from the suspension, so that it's not under full pressure when car sits for days. This kind of makes sense, as some air does escape from my car when it sits for several days. Not much but some.
But the air struts and air springs have electric solenoids, where the valve are triggered to open and close. I don't get it either. Now granted, I have a completely new air suspension, and when my car has sat for days, and I start it the suspension airs up just a tiny bit.
And in most cases, the air compressor never kicks on. Maybe, the brains of the system is telling it to let air in or out as needed. After my recent suspension suspension rebuild, we replaced both front air struts, so I don't get as much sag as I used to to get.
I would try an experiment, with the car in the raised setting to see how long it stays up. The should determine if you are encountering sag in just the front or rear or both.

MJBelcher500

Yullie, I never had the front sag. It was only the rear. Some amount of sag in a sealed system would be expected due to change in air temp inside the spring. If the spring is filled with hot air, as it cools pressure will be reduced. Mine was dropping more than it should have to have just been air temp. At rest, the spring solenoids must be open for sag to occur due to a leaving distribution valve.

Yuille36

I had front sag, most noticeably on the passenger side until I changed out both front air struts. If your rear are sagging, it's most likely air is leaking from cracks in the rubber membrane of the air spring.
This happened to me a few year ago, until I changed out the bags. I had that low rider look going. But, I do agree with your assessment, some sag is expected and acceptable. More than that, you have an issue.

MJBelcher500

I think you missed the part where I have already replaced the springs and still had the rear sagging after being parked for a week. After I replaced the valve (knock on wood) and compressor it seems to be ok now.

Yuille36

And you would be absolutely correct.

nd-photo.nl

For me, a leaky airline also enabled the rear to sag in my case (airline from compressor to valve block). The airbags in the rear are both new. The valve block will be replaced in due time, right now it works well