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Instructions for DIY repair and replacement of S212 air suspension


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The car model is E350CDI.

Disclaimer: This article does NOT provide instructions.
This text is just to convey my own experience.
It is important to consistently consult with an automobile expert.

Background information: The 2012 Mercedes S212 estate is equipped with air suspension on the rear axle, however it does not have adaptive damping control.
The automobile is an E350 CDI, however it utilises the same components as other vehicles on the 212 platform.
The automobile has accumulated a mileage of 223,000 miles, mostly inside the United Kingdom.
The automobile comes with a complete service history from Mercedes and has been serviced only by Mercedes specialists.

Symptoms: Approximately three months ago, during really cold weather, the back of the object descends simultaneously overnight. Subsequently, the frequency of occurrence increases, resulting in a decrease of around 5 millimetres per hour. The compressor continues to activate in order to elevate the automobile, ensuring smooth operation throughout any trip.

The narrative: I conducted extensive internet research, using platforms such as YouTube, Facebook, forums, and also sought advice from authorised Mercedes dealers and experts. The conclusion is that it might include any possibility or every possibility. I have returned to the initial starting point.

Evidently, there exists a leak (or several leaks) inside the system. The most challenging aspect is locating it. Regrettably, the soapy water I created did not reveal any signs of leakage in the vicinity of the compressor, pressure lines, fittings, and the bags. The inference is that there is likely a minuscule leakage or microscopic fracture present.

Given the big dealer's hourly fee of £110+VAT and the local independent's charge being not much different, I made the decision to handle the situation myself.

The investigation: This is perhaps the most labor-intensive aspect of the whole procedure, since it involves identifying the source of the malfunction.

The earlier soapy water test did not provide any results, perhaps due to the difficulty in seeing the air spring and lines when they were installed on the vehicle. This is because a significant portion of the pressure line leading to the right air spring is concealed beneath exhaust heat shields.

In order to thoroughly investigate the matter and avoid repetition, I made the decision to detach both the air spring and the pressure lines from the chassis.

According to the proper procedure, it is recommended to use the Mercedes diagnostic system to relieve the pressure from the system before doing any tasks on the pressurised system. However, I personally opt for a more practical approach by gradually loosening the fittings at the valve block. Prior to releasing the pressure, I loosened the larger pressure line at the pump's terminal and submerged that end in soapy water. After waiting for five minutes, there was no indication of air escaping from the valve under the pressure exerted by the bags. I believe that valve units are an improbable source of the leak.

Once the pressure was relieved, I proceeded to remove the pressure lines from their cable ties. Subsequently, I made the decision to replace the original zip clips with universal brake pipe holding clips, as well as using certain zip tie techniques that I have acquired from my years of experience. The purpose of this is to prevent the pressure lines from experiencing friction and to ensure their stability.

Removing the air spring is a straightforward task provided you are familiar with the necessary steps. When the pressure in the air spring is depleted, the rear suspension retracts to a position that may require significant effort to remove the bags. Since I didn't have any assistance, I reattached a single wheel nut to the hub. Then, I used a 17mm deep socket and a metal tube (which coincidentally happened to fit from my jack) to increase the leverage. I effortlessly removed the sacks by sitting on it.

By immersing the bags and lines in a container of water, I quickly identified the sources of leakage. Both bags and the line are experiencing leaks. The pressure line on the right side exhibits a microfracture. Both airbags are experiencing leakage at the crimp rings. The leaks mostly occur at the lower crimps and precisely where the rust is located.

Reinstalling with new air springs and new lines is a straightforward process that only requires following the opposite sequence of the previous steps. A useful technique involves applying initial pressure to the system in order to inflate the air spring. This allows the spring to be securely fastened at the top using retaining plugs. Furthermore, I conducted another test on the system using soapy water to detect any potential leaks at the fittings.

While the automobile was elevated, I seized the chance to replenish lanolin-based fluid film in certain regions that are often hard to reach. The whole task took a total of 8 hours, during which I proceeded at a leisurely pace, indulging in copious amounts of coffee and cookies, while also being intermittently distracted by my neighbor's feline companion. The precise duration required for replacing air springs and pressure lines is likely to be three hours.

After 10 hours of leaving the automobile undisturbed, parked on level ground and secured, a decrease of 2mm was noted. As stated on the w220.wiki site, the permissible rate of descent is 2mm per hour. The issue has been resolved.

Required tools:
An optimal choice for a car jack would be a reliable and stable low-profile model, since it is necessary to elevate the vehicle using a wooden block placed under the differential. Relying only on a single jack in the centre is not secure; it is advisable to employ jack stands instead.
For optimal safety, it is advisable to use reliable and stable vehicle jack stands. Additionally, it is recommended to place the wheels under the car as a precautionary measure in the event of a failure of either the jack or the supports.
A 17mm deep socket is required to detach your wheels. Having an impact gun might be convenient, but it is not necessary.
A 10mm spanner, either a tiny spanner or a socket with a side hole for difficult access, is required. Additionally, a Stanley blade should be used to cut the nylon pressure lines.
A heavy hammer is necessary to dislodge the old air springs.

Required components:
The answer to this question is contingent upon the specific study and unique circumstances involved. It is possible that the range of possibilities is rather broad and encompasses a wide array of potential factors. For my situation, I need a pair of air springs along with pressure lines and fittings.

I chose Aerosus for my air springs since they have discounted air springs available for my specific make and model.

The outside diameter (OD) of the pressure lines is 4mm, while the inner diameter (ID) is 2.5mm. You need Nylon pressure tubes, also known as Polyamide, that are compliant with either PA 11-PHL or PA 12-PHL for the connection. Additionally, they should meet the specifications of DIN 73378 or DIN 74324, as well as ISO 7628. These criteria are in place to guarantee that the tubing is suitable for the demands of a pressurised air system, automotive settings, and meets the necessary thermoplastic specifications.

The left side measures one metre in length, while the right side measures two metres. Despite this variation, the price remains relatively same. Consequently, I purchased four metres for each side, resulting in a total of eight metres, to account for any potential mistakes. I choose to use the colour blue to represent the left side and the colour red to represent the right side. You have the option to use the conventional white ones, however I really like the coloured ones. I continued using the colour scheme of blue for left and red for right, as I had done with my previous BMW F11.

I suggest using the authentic VOSS Quick Connect System 203 for the fittings. The thread size is M8x1. Mercedes does not manufacture these items; they purchase them from VOSS. This also applies to their fuel return line nozzle. I believe that the return nozzle on the diesel injector is the VOSS Quick Connect System 249LB, however I may be mistaken. The VOSS fitting is equipped with three o-rings, two located inside and one positioned externally. Additionally, there is a grip ring with an aperture.

The VOSS fittings are not intended for reuse with new tubes. If a new pressure line is required, it is necessary to employ new fittings in conjunction with a new tube.

The recommended torque for fastening an M8 size fitting is 5+1Nm. The recommended insertion length for the connection is 17±1mm. You may indicate the location using a permanent marker, as advised by VOSS, or alternatively, you can use tape.

Ultimately, I trust that my article may be beneficial to someone.

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Thank you much for this topic, it is quite beneficial.👍

Regarding the lines, can they be acquired via an authorised dealership of MB? Additionally, how do the lines interconnect or link together?

Additionally, is there a reservoir located in close proximity to the subframe inside the system?

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You may purchase them straight from Mercedes. I choose to purchase the items from a third-party provider, ensuring that they meet the required criteria. Additionally, I choose to buy them in metres so that I have extra units to experiment with.

There are component numbers on the pressure lines that I deleted.
The pressure line on the left side is labelled as A212 327 11 45.
The correct pressure line is identified as A212 327 12 45.

Mercedes also offers a repair kit that includes a length of about 1 metre. I am now unable to recall the specific details, however the item in question is a Nylon tube with a brass connecting fitting, similar to the one used for repairing brake pipes. Nevertheless, I am not in favour of the notion of cutting and reconnecting them using a repair kit. This is because the whole length is produced simultaneously, and if one portion develops micro fractures due to ageing and wear & strain, I anticipate that other sections will quickly follow suit.

The VOSS website has an assembly manual, and I have included some screenshots of their QC203 fitting for reference.

Regarding the centre reservoir tank, my model lacks this feature. On the 212 platform, only the E500 and E63 models are equipped with complete Airmatic suspension, which includes a tank that distributes air to both the front and rear air springs. Additionally, the valve block is also different in these models. Replacing the lines in the front will be particularly difficult, as some sections of the pressure line pass through the interior of the vehicle, similar to the S class model.

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Thank you, friend. It seems that the connectors are of the push fit variety. I need to replace the rear air suspension bags on my S211. I have seen a gradual decrease in the rear suspension height during really cold winter months, but not as much during the summer. I will also inspect the lines of my S211 for microfractures. 👍🙂

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Excellent article. Additionally, I had a leakage through the compressor on my device, so it might be worthwhile to inspect that too. There were little perforations on the lines of my vehicle, caused by friction against the bodywork, namely located in front of the compressor. Road debris may also get trapped between the bodywork and aircraft, leading to increased abrasion. It is unfortunate that they are not covered or protected by anything more substantial.

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Excellent article...I am experiencing a problem with the suspension on my vehicle, similar to yours. It is making squeaking and creaking noises. Additionally, I am seeing the same issue when one or both of the rear suspension systems drop overnight sometimes.

Due of my lack of technical expertise, I intended to visit the nearby Mercedes dealership and request them to repair the whole suspension system.However, I anticipate that it will be exorbitantly costly.

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