Oberling

I have a 2007 e550 that has a rear air suspension leak that causes the rear of the car to sit on the ground after about an hour. The front is normal. The pump will raise the car and the car drives fine, however I already burned out the compressor pump by driving the car like this and need to find the leak before it happens again. I have replaced the compressor and the valve block that's located in the front wheel well. I hear no hissing.

I have tried leaving the car in sport 2, and it still goes flat. My understanding is that sport 2 isolates the additional reservoirs (aluminum tanks above the subframe) that often leak. However, I can't find any information on this for certain.

I have tried disconnecting the battery and the car still goes flat exactly the same as it did before. My understanding is that this eliminates any issues with the level sensors and other assorted electrical faults. This also eliminates any possibility that the car is letting air out of one side to compensate for the other.

I'm confused about some aspects of this system, which is making this problem harder for me to diagnose. Firstly, as I understand it, both rear bags are connected together on the same line which runs forwards to the valve block. However, I seem to get conflicting information about whether a break in this line will deflate the rear or not, I assume that it will, but some have claimed that the bags have individual valves which should hold the pressure in the air springs when the car is off. I'd like to know for sure which option is true for this car.

Assuming that there are not valves in the rear air springs, it seems that any leak in any part of the rear air ride system will result in both airbags being deflated. This would include the valve block, the line coming from the valve block, the T fitting, both air springs, and both air spring reservoirs. Is this correct? Further, what happens if the central reservoir located in the trunk leaks? This seemed to have some pressure in it after the car had sat for a week, and the compressor had failed, which would suggest to me that it doesn't leak. However, if it did, would it cause the rears to drop down like that?

Lastly, I likely need to replace the driver's side rear air bag anyways because the previous owners seems to have replaced them without replacing the body clips, and the drivers side bag has kinked instead of folding over itself properly. He told me that he had replaced them recently in an unsuccessful attempt to fix the problem with the car. Is there any issue with only replacing the kinked one assuming that the actual source of the leak is elsewhere? The passenger side bag seems to be performing correctly. I would estimate that there are less than 2,000 miles on the rear bags as he bought the car in June of this year. What about buying a different brand from whatever he used? I'm looking for good enough for now.

Thanks, any information helps. I've never worked on an air ride car before and I don't want to fire up the parts cannon without being certain beforehand that what I'm buying will fix the problem. The nuclear option is of course coilovers, but I'd like to fix the air ride system if I can.

bbirdwell

See attached. When installing new rear air springs, follow the procedure for proper initial inflation. i.e. raise axle to -1.2 degrees angle (outside higher than inside; use an inclinometer app on your phone), initial lower pressure inflation using STAR/Xentry or equivalent, ensure air spring is not "kinked/kicked" to one side (< or >), lower car, finish inflating.
Be sure to calibrate the suspension after replacing air springs and/or control arms. Every time I've gone into the suspension, I've had to recalibrate the ride height at the corners. Again, use STAR/Xentry or equivalent. Takes about an hour.