julahti

I went and bought myself a project GL320 cdi, knowing it has a suspension issue. What is seem to have is a leaking compressor (dryer casing) and coilovers in front and bladders in rear. I have a new compressor coming soon.

So, am I able to keep the current setup by making sure that front height sensors are set to constant high position? Does the system then function normally, so that if rear was low, it would inflate it and cut off the compressor when rear is up?

I really would like to go back to air also in front, but don't have a good place to work on car right now so I was thinking about this as a temporary solution.

WIll this work?

Max Blast

No.

It’ll handle like a pig, it’ll be dangerous to drive because it will not have a functioning ESP system, the ride will be incredibly harsh, upfront and mushy in the back, depending upon the age of the rear airbags. I wouldn’t drive this vehicle, nor want to be next to one in traffic Until you have sorted out two new rear bags and two new front struts but then again it’s a diesel, so why spend any money on it it will eat your lunch with engine issues shortly anyway.

julahti

How about this: skip the air in the rear as well. Nothing strange there as then it would be normal conversion all the way. I already have a set of new rear struts ready to be installed, so I'd think all I need is springs?

Max Blast

You’ll still have a spring rate system that your ESP/BAS isn’t calibrated to work with, which will require resistor tricks to avoid any malfunction lights. Steel springs have been done on this platform and there’s lots of information available on this forum.

I generally do not recommend them as they degrade the supple ride that this car supposed to have.

julahti

Thank you. As of now I really don't care about malfuntion lights, but sure will look into the tricks, thanks for the info.. Just need the car on the road and rear spring to coil swap is easy to do, even shocks aren't that bad to change.

eric_in_sd

I think it depends on the quality of engineering, whether the spring rate is a close enough match at ride height. That said, I have yet to see a coil-over system that I would trust. There are oodles of Chinesium parts out there.

I have my doubts the ESP system is as sophisticated as you think, so sophisticated as to care about the details of the spring rate. It basically just looks at speed, yaw, roll and wheelslip. Roll is affected by spring stiffness, but much more so by swaybars. Suspension geometry strongly affects cornering stability, but that should not be affected by the struts or springs.

Air springs are excellent as far as ride is concerned, though. They have a 1/X spring rate, meaning small bumps are more easily absorbed than large, while coil springs are linear, with the force directly proportional to displacement.

EWT

I'll be the dissenting vote here for coil springs (I wouldn't mix and match). Assuming (which admittedly is a big ***-u-me) the conversion kits give OEM ride/handling quality and that disabling the airmatic system doesn't cause other problems, I'd do it in a minute. My new to me W164 ML550 doesn't have airmatic, and I prefer the feel of coil springs relative to my airmatic GL. More direct feel, less wallowy and never harsh. You don't get the magic carpet ride airmatic gives going down the freeway, but I'm not a fan of that kind of disconnected feel in a car and the coil springs still give a supple ride. Sport mode on airmatic improves things, but ends up being too stiff IMO. The only thing I'll miss about airmatic is how it levels the rear end while towing. I haven't towed my boat with the ML yet, but I suspect I'll get a fair amount of sag when I do. I definitely will not miss the regular replacement of failed front shocks even though my parts cost is $0 due to Arnott's excellent warranty.

julahti

Update: replaced the air compressor and my rear air springs came alive. So now I have this "hybrid" with front coilovers and airsuspension in rear. Drives ok. I ordered coils to the rear, but now since I have rear air working I think I will go back to air in front as well, so deleting what the previous owner messed by converting only the front.

Obviously I have bunch of fault codes for suspension currently, but at least I am able to move the car and it doesn't sit like a frog any more.

Max Blast

Yay

Miguk_Saram

Can of worms. Opened.

There must have been a reason for previous owner to convert to springs. Driver beware.

Good luck.

eric_in_sd

Yeah, if it works, leave it. There are vehicles that do air springs in the rear and coil in the front, for load leveling. To be honest, if I could snap my fingers and make the fronts coil, I would. There are benefits to air, but in my opinion the headaches outweigh.

julahti

the front struts are in worthless shape so I have to replace them anyway. I really don't see any reason not to back to air. Compressor, solenoids, rear work. Don't even have fault codes any longer.

julahti

Back in the air! Literally. Replaced the coilovers in front with air struts and now fully air in front and back now.
Removing those coilovers was not fun. Maybe I am not very good with spring compression tools but to get that last missing centimeter compressed was a pain, but managed affter all without removing the hub. Installing air stuts was a breeze and really don't get why anyone would want to get rid of them. Such a simple system.
Total cost 250 usd : used compressor/solenoid valves from ebay and new air struts from local facebook sellers.

eric_in_sd

Well, good for you. Though I'd be concerned long term about air struts you got for about $100 each.

Air springs do two things steel coils don't: Wear out, and fail catastrophically. They take maintenance and attention, while steel springs only fail if you do something weird like welding on them.

Though the ability to raise the suspension 3" is nifty.

julahti

Those front struts I bought are both brand new. One Arnett and the other one must be chinese.