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Hi folks;
The rear of my 2015 wagon has been sagging for some time, though what used to take 5 to 7 days and was rarely noticed, now takes 1 to 2. The car always sags evenly - that is, both sides drop the same amount. I'll get the "Vehicle Rising" note upon starting the car, and it airs up promptly (so far...).
My question is... if both sides are down, does that point to a bad air bag, or is it more likely to be a bad valve block or some other leak? I'd figured if it was a bad bag, only 1 side would drop, because the system wouldn't (can't?) balance the air pressure. Just want to focus my attention on the likely area when I get underneath the car, as it's now below freezing in the garage!
Hate to say it... but there's a good amount of recent threads (within 1yr) helping diagnose issues with airmatic. The car dropping overnight or a few days means there's an issue. A healthy system will not drop appreciably for a long time (i.e. you'd never notice it even sitting weeks).
The system will re-level itself after parking and locking... "farting" is normal. Front struts are under 1k each, whether MB (reman) or Arnott. Likely struts at this age.
Car parked and locked (key at least 15' away), wait 30 minutes or so
Disconnect the airline (at compressor) between the compressor and valve body. Stick airline end into a cup of water and check for bubbles. Bubbles = leaking valve body. Replace for $300-400 from MB.
No bubbles = likely strut bad.
Last check, spray down all airlines at compressor, valve body, lines and top of strut (where airline enters) to check for leaks (bubbles).
a US E350 wagon has simple load leveling, not the full ADS with the variable shocks. ADS is mostly found on the upscale V8 sedans.
the wagon has specific luxury vs sport shocks and springs, with the SLS air springs in the back.
the rear air springs on the basic SLS wagon can be replaced wish the cheap arnott stuff just fine, the full ADS found on the AMG V8s and such are dealer only.
Thanks... just took a look and did a bubble test on the connections at the valve block (solenoid valve) - definite leak from around the RR (red) air line connector. I tightened the connector slightly... more bubbles... so I backed it off a bit, no bubbles; pulled back on the air line a bit to re-seat it... seems fine (for now... will monitor). Suspect the valve itself is fine (no errors, no issues inflating & levelling), and likely just needs new connectors... are these a standard sort of fitting, or Mercedes-specific parts?
Pulled the cover off the compressor as well... ~7 years and 140k kms, complete with Canadian winters, have taken their toll... the clip that holds the exhaust shield to that cover is literally gone... but all still works; wiring looked good (no chafing).
(My E400 is not full Airmatic... just the standard rear airbags with front coils.)
....and, the rear bottomed out by the end of the day, just sitting in the garage. Going to replace the solenoid valve block as the first thing... just need to source one; cross-referencing to an R-class seems the best bet, otherwise searches come up with the valve block for a full airmatic setup. Not sure there is a difference in part number from what I've seen (number on my part is A-251-320-01-58).
Got the solenoid replaced yesterday, with the Arnott part. Direct replacement, no issues. Car aired up right away - visibly faster than I'm used to (previously, could barely even tell that the car is rising).
But, bags were flat again by the next morning. Will double check connections on the solenoid (was a bit of a rush getting it back together... maybe I didn't seat the lines in the new fittings firmly enough).
I just can't figure what other point of failure could allow both bags to lose air...? (I suppose if both bags had leaks, that could explain it... but that seems really unlikely, that they would both have developed leaks at the same time, and at the same rate.)
trigger squirt bottle, set to squirt rather than spray/mist, pint water with a tablespoon of Dawn or similar dish detergent. squirt it on any suspect fittings, look for air bubbles. Also squirt it on all sides of the air shock, specifically around the bellows, again should be no signs of bubbles.
Got the solenoid replaced yesterday, with the Arnott part. Direct replacement, no issues. Car aired up right away - visibly faster than I'm used to (previously, could barely even tell that the car is rising).
But, bags were flat again by the next morning. Will double check connections on the solenoid (was a bit of a rush getting it back together... maybe I didn't seat the lines in the new fittings firmly enough).
I just can't figure what other point of failure could allow both bags to lose air...? (I suppose if both bags had leaks, that could explain it... but that seems really unlikely, that they would both have developed leaks at the same time, and at the same rate.)
Just an FYI, one good airbag will not hold up the car if one side is leaking, if you were to watch for four hours, you would see one side go down first then the other side follow, that's how it worked for me on my '03 S500 and my '07 S550. Also one of the reasons I bought two E classes without air suspension. I do miss the ride quality. After chasing my own tail replacing one part after the other on the '03, on the '07 I just did all four struts, valve body, compressor at the same time. Big wallet hit, but it was good for another ten years and only one service visit.
Ah... that's good to know. I'll have to go back and check measurements (or do them again)... but it does ring a bell that one side was going down faster than the other. Great tip!
Hmm... but how, though, does the "good" airbag lose air pressure - it's got to escape somewhere, right?
Ah... that's good to know. I'll have to go back and check measurements (or do them again)... but it does ring a bell that one side was going down faster than the other. Great tip!
Hmm... but how, though, does the "good" airbag lose air pressure - it's got to escape somewhere, right?
When the leaking airbag gets low enough, the other gets overpressured from the weight and releases pressure, to where is unknown to me, I never heard either car leaking.
I have however blown one while driving, went over a 2" pavement edge during street repaving a little fast and blew the right rear bag on the '07, that one was as loud as a gunshot!
Last edited by pierrejoliat; 01-07-2022 at 01:44 PM.
My 2016 wagon rear, deflates (audibly) within minutes of parking and inflates rapidly on startup. Is this not normal??
Deflates how much? An audible pressure release shortly after parking is normal... but there wouldn't be a noticeable drop in the ride height. If your car is bottoming out in the rear after parking, and giving a "Vehicle Rising" message on restart, that's not normal.
No update... typically bottoms out within about ~12 hours, though I've had it stay aired-up for as much as a couple of days (which is just odd, that it can be inconsistent). It has been too cold to do diagnostics in the garage... riding it out until Spring and hoping it doesn't get to the point where the compressor needs to run excessively.
It can only leak out of so many places... disconnect the electrical connector from the valve body. You'll get faults, but if it continues to drop... then is a mechanical/part issue and not electrical. Then its a matter of figuring out whether its the valve body, connectors, lines, or springs. All of which has guided above.
So far it has only happened to me once. I let is sit for 24 hours before driving it again and it held it's height. I put the scanner on it and noted the minute counter on the compressor and it hasn't change in 24 hours. I also monitored the ride height sensors while driving and they seem to be working fine. I'm with Fitzbenz at this point, it's too cold out in the garage to diagnose, especially when it isn't actively leaking. I hate intermittent issues.
7 years old air bags, working in harsh/salty climate might be at the end of useful life.
There are several components that can leak, so bottle of soapy water might be a good friend.
Beware that by operating the wagon with leaks is putting air compressor in extreme work duty, so it won't take long till it will give up as well.
When I had such issue on my W211 wagon, I add a Tee to air line, with pressure gauge showing inside the cabin, so I could monitor leaks as well as compressor performance. Than additional line gave me easy hookup for shop compressor and endless troubleshooting.
Having replaced the solenoid valve block to no effect, doing a thorough soapy water test around the valve block, airbag connections, exposed lines, compressor & connections, with nothing apparent, and thanks to a comment above that "one good airbag will not hold up the car" (and most people telling me "it's the bags, stupid")... I bit the bullet and replaced the airbags - ordered Arnott A-2790 (right rear) and A-2791 (left rear) from Rock Auto. Replacement was straightforward - see this thread, including my post - and so far so good, with no sagging after up to two days of being parked. Hopefully I'll have a longer parked stretch to really restore confidence that the issue is resolved.
I haven't had a chance to inspect the old bags... I'll try to pressurize them and see if I can find any sort of leak.
This was just annoying because it was so inconsistent... sometimes the car would be fine for days... other days it would be down after a few hours. Temperature was a factor - was definitely worse in the cold. I lived with it for probably ~2 years since I first noticed... but that first time was the car being parked for a couple of weeks, and then it never really manifested again until last Fall, when it would be down after a few days... as it got colder, it would be down the morning after being parked in the garage at night. It always aired up right away, and I was never worried about the compressor running continuously.
Thanks to those who contributed their thoughts & wisdom.
That's textbook air strut stuff, happened the same way on both my air matics, the rubber folds over itself and has cracked, so leaks depending on where the crack is in the fold.Glad you got it worked out!
Found the/a leak - it is a slow leak under the band clamp where the bag is clamped to the plastic mount... those little bubbles above (under?) the "02" would percolate away under even low pressure (10psi):
This was on the right side rear bag. Don't think there's anything to be done for fixing that... but there you go.
12-28-2021, 10:06 PM
