Brent Castel

Hi. New to this forum, but haven't found any existing thread that answers my question so far. Hoping someone here can help. So, had leaking rear air springs, replaced them, problem solved...until, first time I used the 'raise vehicle' function, about a year later, and the compressor would not shut off until I lowered the vehicle back to normal height. Since then, the left front air spring is sometimes losing pressure overnight, or more quickly on occasion, or not at all. Here's the weird part: as I'm driving, I can hear the compressor running (windows open, around town) but it only starts as I reach about 40 km/h, and it always shuts off as I slow to a stop, around 10 km/h. I don't know if it's running all the time above 40 km/h, because I can no longer hear it, but I assume it is running a lot because the compressor is sounding tired. Does anyone know if there is any good reason why the Airmatic control system would be speed sensitive? I've tried all the usual leak detection methods and found nothing so far. I'm beginning to suspect a control module error. Where do I find the control module, so I can disconnect and see if the problem resolves? 2012 GL350 with ADS.

Any suggestions greatly appreciated.
B.

TX07GL450

When was the last time compressor was replaced? If you can hear the compressor while driving, it's cry for help to be replaced. And that is most likely your problem...
Left front strut leak might be a problem in itself, especially if it is old.

Max Blast

Left front strut airbag is leaking, replace it and then the right one.
Then replace your compressor if it won't raise it.

If you've been driving with a leaky bag for a year the compressor is most likely done.

Brent Castel

Some of you are likely going to cringe when you read this, but it seems like I found a very inexpensive temporary fix for leaking airbags. I'm a cyclist, and I use tubeless tires on my bikes, but bike tires are not completely air tight, so you have to add liquid sealant when you install the tires. The stuff I use is called Stan's No More Tubes, and it works great at sealing up the tires initially, and also plugging any subsequent minor punctures. This got me thinking that this might work on MB airbags, and I proceeded to put about 2 ounces of sealant into each of my front airbags. After 2-3 days, no more sag. I mean it's GONE! Seems the sealant found my leak(s) and sealed them up. System works fine now, with raise and lower happening as quickly as it ever did. I actually did the same to my rears last year and they've been perfect ever since (lied in my first post). Call me crazy, but $30 worth of sealant beats the hell out of replacement airbags on an 8 year old vehicle.

BUT.....the compressor still seems to be running for no reason that I can see. As I said before, it doesn't run when I first start the vehicle, but it starts up at about 40 km/h every time, and shuts off at 10 km/h, for the first few minutes driving around town. Hit the highway for a bit, and rarely hear the compressor again until the next cold start. Does anyone know if this is normal? I know, the compressor is tired if I can hear it, and I intend to replace it, as soon as I figure out if there is something else that is causing it to run in some speed dependent mode that is not normal. Likely I could replace it, and the new one would be so quiet I could assume the problem is solved, but I really just want to know I'm not going to burn out a new compressor.

expl0rer

hat i the I won't chastise you for the hack. I think it's impressive if it works long term with no safety implications. A couple of thoughts.

1. What is the pressure rating for the sealant? If the pressure in the Airmatic system exceeds the pressure rating of the sealant, or maybe even close to the upper range, it might not hold well and you may have a safety predicament on your hands while on the road and at highway speeds. I don't know the op and max pressures of the airmatic off hand.

2. When you lower the Airmatic, the pressure is released. That makes me think that the air flow could also move the sealant along the release path and now you have it in places where you don't want it and maybe sealing passages you did not intend to have sealed.

Max Blast

Yikes. You’ll have more problems when this green snot starts gelling and solidifying in places it should not be.

your compressor needs to be replaced. It is speed sensitive and will shut off when coming to a stop, unless you are actively raising the vehicle. But running all the time means it needs to, in order to generate the pressure the system demands.

Ohbtw your new compressor might fail prematurely from chewing on green slime that has been backwashed into it, or from trying to pressurize a clogged system.

this is supposed to be a dry system.

total repair cost to have done it right would have been less than a thousand, if DIYed, just saying.

this is probably the only corner case where I’d recommend a steel spring conversion.

expl0rer

Nah, toughest part would be to rerun the lines when replacing them, but at least you don't have to find your way, just follow the existing path. It will cost, though, in DIY time and new parts.

cartunes25

For anyone interested, the Mercedes shop manual says the Airmatic pressure varies with load but the operating range is 80psi to 145psi. I have found that on my GL550 that the normal pressure is 113psi per corner with no load, just me in the driver seat. This is verified with shop DAS. I ran full end to end testing using the Mercedes tests and everything is operating normally.

I found this information after having rear bag explosions while towing. The aftermarket product I installed failed, the manufacturer claimed, insisted in fact, they were compatible but the MAX psi of the bag was already exceeded by the normal operating pressure of the GL. I am now in the situation that I have to again replace all the airbags of the suspension, this time with the OEM Bilstein parts.

expl0rer

Interesting information. Thanks for posting it. Do you mind me asking which brand you have had explode under towing load? Amd what were your towing? I don't tow or load the vehicle a whole lot, now, but if I did consider that at a later time, I'd definitely like to avoid this problem.

cartunes25

The brand I bought is Arnott. I am towing a 28 ft travel trailer with weight distribution hitch. I have weighed everything and the trailer comes in at just under 700lbs tongue weight. I am also using Tekonsha brake controller.

I have the Arnott brand Struts in the front and only the Arnott air bags in the rear. To me its quite clear that the Arnott model is an inferior product. The first blown Bag I called them to discuss this case exactly and they ensured me it was just defective.

An additional point to the OEM Bilstein bags, they have a MAX of 195psi.

eric_in_sd

Especially effective considering that the air bag is filled from the top and the leaks are at the fold, which is at the bottom.

Might not be a bad idea to get a can of this stuff and keep it in the vehicle in case a bag blows while out on the road.

I ordered a bottle of Orange and will stash it and an irrigation syringe in my trunk.

expl0rer

That's quite a bit of a difference in the max pressure rating between the two brands. I have one Arnott bag now and two Arnott ADS hydraulic shocks in the rear, the others are OE MB from the factory - 10 years old and holding up for now, but likely will need attention.

I am not familiar with the GL's towing settings, I am assuming you can't switch the bags' height to reduce the pressure in the system when towing?

Brent Castel

To be clear, the sealant I used is a thin, white, milky liquid, in fact latex, and not the green 'snot' referred to above or the Orange here. I fully plan to replace the airbags, but now reading about potentially exploding Arnott bags, I hesitating. Almost ordered the Arnott's yesterday, but hesitated, looking for opinions here. Insist on Bilstein, or will the Arnott's work?

eric_in_sd

Forget about it. After OEM, Arnott is probably the most common installed. The bags aren't in some weird habit of blowing out.

If you go back through the thread, nowhere does it say the Arnott bags have a lower maximum pressure than any other. If the pump is only able to get to 145 psi, a maximum psi rating of 195 sounds about right, though maybe a little close. The actual blowout pressure would be far higher.

The sealant doesn't have a pressure rating, per se. It flows into cracks in the rubber and bonds. The pressure tolerance would be dependent on the size of the fissure it is filling.

I really doubt you'd get any liquid sealant regurgitating itself all the way back to the pump. It will settle at the bottom of the bag anyway.

It seems to me that wetting the outside of the bag, especially the fold, with some rubber protectant, such as Armor All, might not be a bad idea.

Edit: Looks like the Arnott bags do in fact have a maximum working pressure of 100 psi. Oops.

expl0rer

In my humble opinion, if you don't tow, you'll be alright with Arnott. If the cost of Bilstein is marginally higher and peace of mind is worth it to you, go with Bilstein. I generally am OK with paying more for parts I know are better, but not all the time.

I'm currently running one Arnott airbag in the rear now and three OEM. Since the only thing I have that needs a tow is a boat but that's 11000 lb dry so way over the GL's capacity, I don't plan on towing anything, really, and the heaviest I'd have the tail end would be with camping gear, which may not exceed 200-300 lb. Plus three souls on board.

eric_in_sd

Well, yeah, but that kinda misses the point. It's not if you don't tow; it's if you are willing to rule out towing.

Personally, the only time in which I really have enjoyed using the GL is when I've been using it as a truck, and that includes towing. Talked to a buddy about potentially meeting for a road trip and, when we meet, putting his car on a trailer and towing it with the GL. I'm suffering with all the intricacies of this truck so I can use it for its full capabilities, not dial it back to 75%.

expl0rer

I totally see your point. My thought is that everyone buys this truck for particular reasons and mine seem different than yours, and perhaps a good part of the X164 population. My main reasons for purchasing the truck (yes, I refer to it as a truck as well, and regularly at that) was its 4x4 capabilities and rear cargo area. I had grown tired of moving loads of tools and supplies in multiple trips with a station wagon when boat launch and winterizing approached every year and didn't want to be stuck in a sand lane waiting for someone to pull me out. Towing was not on my list of things to do with it at the time and I doubt that I will own anything that I would tow with the GL. I've toyed with the idea of a camper for vacations, but would rather AirBnB instead, especially since it's only three of us, and one soul is a dog. A camper would add one more thing for me to maintain, and as OCD as I am, the boat and cars take up enough of my time. I am not getting younger, so adding to my to-do list is frowned upon, especially by me!

I immensely enjoy the convenience of three zone climate control, so the dog and my wife can freeze at 18C or below year round while I can select a balmy 23-24C. Everyone can have their own airflow customized to their liking. Although the dog is often hanging out the rear window, but even then I feel in a temp controlled bubble, especially in the winter with the heated option engaged on my seat. I don't care much about the ventilated seats, but they're a great invention according to my wife. She also has them on her daily driver, I was obligated to find a specimen with those.

The intricacies are just part and parcel with any vehicle. We all put up with them to an extent with every automotive purchase. I could do away with some of the MB technology and complexity, but then I would have ended up in a 15-20 year old Defender 110 which would have cost more upfront, and I would not have the benefit of three zone climate control. I think driving a Defender in city/highway conditions only or mostly is just pure and plain sacrilege.

eric_in_sd

All good points. I didn't mean to sound harsh. My irritation stems from the fact that Arnott does not provide low-cost components. The implication is that they are designed to operate as OEM or better.

The truth is, no complicated machine is designed to operate extensively at 100%. For example, I wouldn't run the motor at power peak all day long. Tow loads don't suddenly become unsafe when crossing to 7501 lbs. One of the reasons a normally aspirated V8 can last so long is because it can be driven at small fractions of its maximum power output.

Still, it's nice to know that power output is available when I need it for a pass on a mountain road - not fretting that my 100 psi rated air bag will go kaboom when I need it.

The air bags are a difficult design. The fold at the bottom makes for a great deal of stress on the rubber at that point. Air springs on big trucks are like big pillows, a lot like the tires. Too bad MB couldn't have created a design that doesn't fold.

expl0rer

I didn't think you sounded harsh at all. Your post came across with the soft and sleek voice of Morgan Freeman! lol I had the option of James Earl Jones, but I didn't feel in a Darth Vader mood.

Considering the cars can be raised and lowered, airbags with folds may be the only option from a design perspective. I imagine all cars with air suspension will suffer from this. Maybe even the weight of the vehicle could be a factor - more weight, more wear? I am not sure about the latter, though.

I am not knocking Arnott. I am running two shocks and one bag from them, all in the rear. Mostly because of recommendations/posts on forums. If they are designed to operate at OEM level or better, the best way is to compare how many bags they have replaced under warranty vs. MB's replacement numbers, and even then we may not have a good picture. But I don't see MB or Arnott releasing such numbers. My bags, I think are 10 years old. So MB would not have touched them. In my microcosm, if I could ride on the Arnott bag for 10 years, that would equate to OEM quality. The caveat is that I would not tow anything, and I am not sure that the previous owners did or not. The hitch does not seem to have been used a whole lot, if any.

eric_in_sd

lol gravelly voiced serious black man at your service

The bags I've seen under semi trailers are a double pillow. It's difficult for me to imagine why that wouldn't work for a very, very long time. Folding the bag under is brutal - rubber doesn't like to be deep flexed like that, as anyone who has ruined a tire by running it while low on air can attest.

I can see it would be difficult to do a pillow combined with the strut, but there's no reason it couldn't have been done on the rear.

On the front, I don't understand why they didn't just do a large diameter gas piston strut. Gas pressure shocks last a long time. If you have 150 psi to work with, you could hold up the corner of the truck with just 10 square inches, or a circle 4 inches across. I wouldn't be surprised if the Baja shocks are already 4" diameter. Maybe that would be too expensive, but this is supposed to be a Gelandewagen Luxus.

expl0rer

Obviously, I am not very knowledgeable in airbag design. From what I gather, making the bag wider and shorter would make up for the shortcomings of the current design. I bet the designers and engineers had it right, but maybe marketing butted in and quashed the idea and I wouldn't be surprised if accounting came in after and buried it deep into oblivion.

Considering the G design had not changed much in 40 some years, until 2020 I think, yet it is priced in the 150-250K range, I am not surprised that its Luxus variant may have fallen victim to numerous cost cutting initiatives during design in favour of production.

eric_in_sd

MB has a tendency to make fancy things because they can, or to come up with new designs even though proven technologies are out there. I'm not sure what motivated them to make a folding air bag, but I imagine the engineers thought something like, "Well, it COULD work. Let's do it!"

It is difficult to compare tech in the G versus the GL. MB was, I gather, frankly mystified by the public's fascination with the G, and basically said, well, if you insist. They kept it as sort of a rolling advert for MB. Note that the U.S. sales of the G are about 1K/year, while the GL sells 20x as many (2010). So with the GL there is incentive to cut the per-car cost, because $1 saved on the GL equates to saving $20 on the G.

MB isn't super smart about holding costs down. There was no reason to include fiber optics in the audio system, for example. Or a motorized cover for the CD & DVD slots. The design of the air suspension is simply a mystery. Maybe the suspension guys got infected with greed whereas the engine guys refused to compromise.

expl0rer

I wonder if they "borrowed" the suspension design from other models or even other brands. The S class, I believe, has been on airbags from before the GL came about. Maybe they just tried to beef it up. And the Touareg (first gen) had air suspension with raise/lower function as early as 2004. I would not be surprised if MB went to Bilstein and said "show me what you have on the shelf or in development for air suspension?" Of course, some modifications to differentiate it from competitors and make it "MB only" would probably be in order, but overall I would think that MB would not try to invent the wheel over and over. I could be wrong.

I am not sure about the fiber optic on the entertainment system. I do think it's overkill. But at the same time, the few times I have mentioned it, people are genuinely surprised as in "that's cool". I don't particularly think so, since I would be dealing with the costs if/when some component in the loop decides to say "buh-bye". On the up side, every time things break, there is an opportunity for upgrades.

expl0rer

A brochure from Bilstein about their bag/strut gives a look at the Bilstein design.

https://www.bilstein.com/us/wp-conte...97_EN_VIEW.pdf

eric_in_sd

Thanks dude

Couldn't make heads or tails of the verbiage about the air bag. Something about cross-ply being bad and low rolling radius being good. Curious fact is they all use the same folded bag design, shrugging off the wear and subsequent bag failure.