alx

I know it doesn't make sense. I dont know how airmatic makes decisions as I am sure it is proprietary, but i think pressure is the basis and height sensors are used for quick adjustments. This unless you perform airmatic recalibration wth DAS it likes to maintain certain pressure in each shock and use the height sensors for quick compensation during dynamic transitions. So a stiffer bag will tend to sit higher a lot of the time as airmatic knows that xxx psi for that corner is the baseline.

N_Jay

That would be so wrong the way to design a closed loop system.


As the bag wear, temps change, load changes, etc.. you would get all different kinds of levels.


What I am quite sure they do is when they need to adjust level, (triggered by some event) they fill or bleed the bags (each corner individually) till they get the desired height feedback from the level sensor.
That is why a new bag or an old bag, a loaded car or an empty car, a hot day or an cold day end up at the same height.


AND Arnott says the spring rate in the same as OEM.

alx

Oh, agreed. But here I am telling you that arnotts in the rear sit higher unless you recalibrate with DAS. I have seen quite a few truck like that so it is not a fluke. Including my personal x164 which now has arnotts all around. I had to recalibrate the rears to bring them where they needed to be (about 3/4" lower give or take)

samiran

alx,

I'm not sure, so I don't want to necessarily take a position on this, but. . . .

I would guess there is a PID control program in the ECU that adjusts the pressure based on the height, and that the control program is a "fuzzy-logic" learning type.

I don't know much about ECUs, but I have some experience with industrial control systems, and this is a pretty normal thing.

If that is the setup, then it should start wrong, but over time (50-100+ adjustments) the calibration should sort itself out.

I would guess that DAS recalibration is the right thing to do, and solves the problems quickly and accurately (I saw the DAS step in WIS, but unfortunately I do not have the programming unit).

The only reason I'm guessing this is I'm assuming that over-time, the system will adjust for various changes, tire changes, and the profile of the bag. There cars have a lot of PID loops, and most of them seem to be self-training (fuzzy logic).

What happens, specifically, is that there are some constants that are used to calculate the adjustment rate for the variable in question. Over time, the system measures how well it is reaching its target (height, in this case), and then makes very small adjustments to the constant to try and "tighten" the match. I know the transmission does something like this, as does the throttle response.

Just my 2 cents, and a wild guess.

Bimmer777

This thread actually turned into a pretty good discussion.

I am replacing both rear bags tomorrow with Arnotts, so I there wont be an experiment there. However, previous owner replaced one of the fronts with Arnott leaving the other side OEM. I can tell tell you that I honestly cannot tell a difference at all between the two sides in terms of the ride quality or the height difference, whether when driving or after sitting a while. I dont know how long ago the previous owner replaced the front bag, but maybe there is some merit to what Samiran posted above on system adapting.

alx

i think the front arnotts are actually identical to oem. i almost want to say that the fronts arnotts are remans, but not sure.

the rears however are not. they look very different and feel very different even when fully deflated.

N_Jay

The Arnott front shocks are reman but the spring portion is new (Arnott).
It looks like the identical design as OEM.


The rears seem to be a slightly different design from OEM.
I have to take a look at them loaded to see what they look like.

BlownV8

The rears are definitely different than oem.

Bimmer777

Today was a productive day. Changed rear bags, engine oil, cabin and air filters, and the fuel filter. Came away very positive - this car doesnt seem hard to work on at all.

Bags change were a breeze. I mean, couldnt be a simpler job. Just tight quarters to get the air line off, otherwise cake. When I started the car first time, bags started inflating but then stopped and there was an malfunction message on the dash. Restarted the car, tried again and worked like a charm. Car was slightly rooked at first but then settled in perfectly level after the test drive.

Cabin filters - went through the glovebox on my C63, decided to try the under the hood method on the GL. Under the hood method is definitely miles easier. No brainer here.

Fuel and Air filters - a bit more work involved here obviously. Have to say that nothing is hard though, just a bit time consuming. But pretty straightforward and nothing really that hard to reach. I did take off the cross bar to make everything easy. Not a big deal to take it off and much easier to work without it.

Started at 10am, was finished by 2pm working very slowly, taking many breaks (distractions from work and gf), and a short test drive in the middle to test the bags. Will be much faster next time.

Next service will be likely in summer when I change all differential and transfer case oils, and the transmission. Looking forward to it.

alx

unfortunately, the air filters on the om642 engine are baselined when new and as such engine adaptations need to be reset every time you replace them. failure to do so will result in your future service requests be messed up.

cliff notes: you need star/das to replace air filters and let the system know you have done it or your next real service "b" will be displayed as a "c" or an "f" or something else depending on the phase of the moon.

mb_rpl

Hey guys, the Arnott air spring replacement set (4 air bags and a compressor) came yesterday. Getting ready to install but wondering if you guys have the torque settings for the bolts involved. I tend to strip bolts very often so I rely on my torque wrench to avoid strips. TIA.

samiran

alx, does this mean that the reset in Assyst Plus is not sufficient?

This is a really big pain in the butt. I used the procedure posted in the forum here (previously), and did not check WIS, but I see it there in WIS, plain as day.

It seems like it is worth buying a knock-off chinese Star Diagnosis to be able to work on these diesels. I hate to buy it, but I'm surprised (genuinely shocked, would never have thought) that replacing an air filter would require accessing the ECU.

This should be a forum sticky, given the number of people that are using the DIY procedures (here and in the ML350 posts) for air filter replacement.

samiran

Update: Just replaced the "burst" air spring. (Going to replace the other one tomorrow).

I tried to follow the Arnott instructions exactly, including the end lower-raise instructions.

Took about 45 minutes total. A couple of tips:

1. Removing the air spring is dead-easy. Once the vehicle is lifted and wheel removed, you can manipulate the air spring to make accessing the airline fitting easier.

2. It seems like a tight fit to install the new spring, but it actually isn't. The air spring feels too tall prior as you are maneuvering it, but it is super easy to compress it, which makes fitting it easy. Make sure you don't push it against any sharp parts!

3. Pushing the airline in seemed to work fine, as long as I tried a couple times. It feels just like a shark bit plumbing connector. Push hard, and the airline will insert to a point. Push slightly harder, and after some resistance the airline will insert slightly more (maybe a couple CM). I did not have a serious problem inserting the airline from the side, using a standard hydraulic floor jack.

4. I don't seem to have any of the leveling problems others did. When I first started the vehicle, the new spring was lower than the other side (OEM Bilstein, in working order). I waited the prescribed 2 minutes, then raised the vehicle. Still not level, but slightly closer. Raising the vehicle permitted me to remove the floor jack.

I then lowered the vehicle. This took forever (5+ minutes), which is abnormal; however, once it was lowered, it was *exactly* level. Verified with measurements and a spirit level. I checked WIS, and there is nothing about using STAR Diagnosis to calibrate the airmatic system, just use it to check for errors (leaks and the like, I imagine). This is not to disagree with alx; if you have access to one, you probably should. The Arnott springs looks and feel quite different from the OEM ones; I'd be surprised to see that they don't require some level of adaptation, somehow. It may happen automatically, but it seems prudent to force it if you can.

I'm going to take it for a test drive in the morning tomorrow, and then probably change the other spring. I'll report back if there are level problems after either operation.

In case anyone was wondering, the exploded spring was an OEM Bilstein, with the Mercedes logo. As far as I can tell, it had not been replaced, as was original. Frankly, given that these things are pretty cheap (from Arnott, anyways), and how much it would suck to have one burst while driving, I can't imagine only changing one. In fact, I'm wondering if it is advisable to change both of the them at ~60-80k miles.

Bimmer777

Unfortunately I dont have access to star/das and I am not really willing to go to the dealer to pay $ just so they reset my service computer. Wont lose sleep over it as I am pretty sure i can count 10k miles and know what service to do without the computer telling me what to do.

mb_rpl

Hey Bimmer, what torque settings did you use for the different nuts and bolts involved in changing the front air springs? TIA. Looking to replace today. Thanks!

Bimmer777

I just changed only the rear bags so didnt have any nuts and bolts to deal with. Arnott has an installation video on their website. I am at work so cant view youtube, but check it out and see if they mention it in the video.

mb_rpl

Unfortunately, it only mentioned to tighten it according to manufacturer's specification.

Bimmer777

No help then. Suspension part I wouldnt be too afraid of stripping or over tightening. They are all pretty solid bolts and designed to withstand heavy loads. So I dont think you should worry too much. Of course if its a smaller non-load bearing bolt, dont go crazy on it.

alx

According to mb failure to reset engine adaptations when air filters are replaced will reduce engine performance and effiency.

Bimmer777

That's a bit more serious. I can understand that the motor initially wont run as efficiently but does that mean it wont adjust after a while? I have a hard time believing that such a sophisticated system wouldnt adjust itself.

I may try to give a call to local dealer and ask them how much it would be to reset computer.

samiran

Yeah, if reseting the service menu does not reset the engine adaptation, that makes sense.

There is also a note that you should not replace the air filter more often than required, as the engine adaptations assume a certain amount of build-up on the filter (over time), and adjust the engine parameters accordingly. Accelerated wear may result, apparently.

I would guess this is a $100-$200 reset, IF the dealer is willing to do it.

Bimmer777

Yes, I dont really want to deal with the dealer and trying to persuade them to do this for me. I'll drive it some more and see. So far, 36 miles on it since the change and MPGs and everything else seems completely normal. About to put on another 70 miles tonight.

And my filters definitely needed the change...

KrustyKustom

Great Thread! Finally.....guys who work on their GLs!!

My filters are ready to come out at 20k, the design scoops up butterflies, leaves, and everything else that is on the road. I found the best price at Pelican parts.

Bimmer777

Got new set of wheels and had a chance to put them on today. They are stock 20s but I think they will be very good balance between looks and comfort/performance. One non-maintenance item i've done. Love the updated look, and i really thought the 18s were a tad too small aesthetically on this truck

Why I am posting this in this thread I dont know, but here it is.

N_Jay

Installed the new shock.
Not really a big job.
Fells fine with one new shock and one old one.
Odd thing is that the shock pulls itself in instead of wanting to expand.
You are also supposed to replace the nuts since they are friction fit (slightly crushed).
I just used some locktight blue.