mpovah

Hi,

On my 08 GL 320 CDI we replaced the rear suspension with Arnott bags which I have always had good luck with.

Right away the driver's side one burst when the car came down off the lift. We assumed it was a defect. Replaced it, this one burst as well. The third one lasted a day or two then burst. This is not a defect, something is causing it to burst.

Has anyone encountered this? It appears to split up the back. I am wondering f the lower control arm in the rear is possibly bent and when it actuates it is twisting the airbag causing it to fail. Really pulling our hair out with this one - any advice greatly appreciated.

Thanks,
Matt

eric_in_sd

Be methodical, not speculative.

Was it popping air springs before? Have you asked Arnott what they think? You are not having a problem with the passenger side spring? Swap it to the driver side and see if it goes bang.

mpovah

It hasn't ever popped them before to my knowledge, although the reason we replaced it was one of the old ones had failed and it was identified as failed when the car went in for an oil change. The one that had failed was the left hand side one, same side that they are popping on currently.

The car was exhibiting other symptoms previously - there was an unexplained major sway in the rear end when driving. Felt like the rear end would waggle while driving.

I haven't heard from Arnott - will ask the shop if they have communicated with them.

Passenger side spring seems OK. I wondered about asking if they had swapped the spring across to the other side. The issue I guess I am worrying about with this plan is these things are $500 each and if it pops another one I am not sure I can afford to keep replacing them.

mpovah

Shop is recommending a coil spring conversion kit, but I would like to know why it is happening. I was hoping someone else had seen these issues before. I mean, what reasonably could cause these things to pop, brand new out of the box?

rapidoxidation

Can you tell if the ride height is way taller than it used to be on that corner? In other words, is the height sensor working properly? If the car thinks the rear end (or just that corner) is too low, might it not keep trying to inflate that bag to correct the perceived low height and thusly overinflate/overpressurize/pop the bag?

BlownV8

Was thinking the same thing. Ride height sensor is thinking it is low and the bag is getting overfilled causing it to pop.

Sallad

Find a different shop, these guys are lost and trying find an easy way out.

I agree with the over inflation theory.

Max Blast

Get it out of that shop stat.

i subscribe to the over inflation theory. When it bursts, is that corner higher than the others?

something is telling the valve block to let more air into it, and that usually is the level sensor.

yiu can visually inspect it to see if it is overtraveled and also read it out with an mb compatible scan tool to see if the signal it’s putting out is noticeably different that the other three.

if it isn’t any of the above the next culprit is a seized or leaky valve block

mpovah

Thanks for all your responses!

These are all good ideas and I will ask about all these points. I have been working with this shop for years and know that they are honest. I do share your concerns though that they don't seem to have an answer except to develop a workaround.

BlownV8

Honesty is not the question, it's competence.

mpovah

Wanted to post an update. Have been in touch with the shop and they had already ruled out the ride height sensors and the valve block. They have done a deep dive, checked the voltages from the sensors and even used the computer to show the actual air pressure in the bags when the system is inflated. One side apparently does not rise higher than the other when the issues occur. The split in the new bags has always been along the seam apparently. They are really scratching their heads as well. Is there anything else that could cause these problems? Could the computer somehow misreport the air pressures in the bags? If something was bent could it cause the bag to twist somehow and pop? I am really stuck here and greatly appreciate your input.

eric_in_sd

The only way the pressure can rise above nominal on any particular spring is if the spring is stretched upward to its limit. If this had happened, the shop should have noticed the vehicle going super tall on one corner.

Checking the pressures is a little tricky; you need a bidirectional tool that will send instructions, because it has to open the particular spring's valve to read the pressure. The pressure sensor is on the valve block manifold.

To my knowledge, the system does not check pressures on the springs. It only monitors the reservoir pressure, particularly when refilling the reservoir.