bmwpowere36m3

Recent airmatic threads got me thinking... I've got a dropping rear end (both left/right) on my E550 that needs addressing. Ran all Airmatic tests in Xentry, all passed, not surprised. Sprayed soapy solution on all airlines, airline connectors, valve body and rear air springs.... nothing. Disconnected airline between compressor and valve body... very slight leakage. Replacing valve body anyway, but not convinced its the primary source of my dropping rear end. Any leakage out the valve body thru the compressor line is negligible if the vent valve in the compressor is good (which it is).

The E550 is a 2011 with 100k, figure its cheap insurance to replace the rear air springs. Sure enough, after cutting the protective bellow and applying soapy solution... air leak was found. In this case, the air was leaking between the nylon end cap and rubber bladder. Either the rubber has hardened and/or shrunk and/or the crimp ring has lost tension.

So, what did I learn... spraying soapy solution on the rear air springs is pretty much useless for micro leaks unless the leak is at the airline/connector going into the nylon end cap. If the leak was significant enough, I suspect you would just hear it in the vicinity.

protective bellow removed from air spring


air spring exposed, rubber bladder folds over itself on both ends


view of lower fold, rust and debris collects


leak exposed, coming out of upper fold of rubber bladder


air spring inflated to expose crimp rings under "folds"


same leak as above, can now be seen coming out of crimp area


Since I have another one, I'm going to attempt to remove the protective bellow without damaging it. The idea being, if someone can remove the bellow, test for leaks and put it back together if its not the issue. What I think might be beneficial for testing, especially the front struts due to cost, would be something like this taken from W220 wiki site. Basically an airline fitting on one end, schrader valve on the other and maybe add a tee with pressure gauge in between.



Now granted, all that work and knowing the rear air springs commonly fail once you near 10 years / 100k miles or so. As others have suggested, just replace the air springs if your nearing that age/mileage and suspect them of leaking.

pierrejoliat

I had one air spring that popped when I went over a lip of asphalt in a resurfacing operation, went off like a gunshot, the other three that I had fail in my "S"'s were top seals by the airline connection and on the inner seal like those, just degraded rubber from age and wear I guessed. even when spraying soapy water on the top seals, they didn't look like they were leaking, but they were from very small cracks, which I found after removal with air pressure.

MBNUT1

What is actually leaking and can it be resealed?

bmwpowere36m3

In my case the connection between the rubber bladder and nylon end cap (you can see the bubbles foaming). Hypothetically with a new, potentially slightly smaller, crimp ring it could be possible... You could also pour in tire slime into the bag hope it seals... Reality is they are not serviceable, when they leak, they are replaced.

5soko

Good work and write up!

MBNUT1

What is the diameter of the bag? 4 inches? Just trying to guestimate the pressures involved.

bmwpowere36m3

At least 1/4 of the cars weight + any dynamic load... I think it operations up to 150psi. The diameter is ~ 4 in at the end cap.

Arrie

The car's weight (~500 kg / spring) makes the pressure about 6.5 bar = 94 psi. During drive it all depends on how big move a bump on the road makes to the spring. If it makes the air spring to go half length then pressure doubles.

bmwpowere36m3

The pressure within the springs certainly can be more than the compressor can provide... I recall the pressure relief on the compressor was ~150 psi or so.

bmwpowere36m3

The other spring had a similar leak and pulling off the boot is possible once the spring is removed from the car.

KEY08

Very helpful diagnosis for those constant Airmatic questions from new members signing up here just to ask why their car is dropping. Nicely done with great photos!