the air suspension system evaluated
 

I have had 2 air suspension 109s and one of the later hydropneumatic 116/6.9s. The ride quality is comparable (since both rely on gas compression as the suspension medium) and was in a class by itself back in the day. The pricipal advantage of the hydropneumatic system (developed by Citroen in the 1950s from which the Mercedes system is a direct offshoot) is that it is a CLOSED SYSTEM. All adjustments for ride hight and load are by adding or subtracting hydraulic fluid from the "accumulators," which are spheres devided by a rubber membrane with compressed nitrogen on one side and hydraulic fluid on the other.
The air ride system, on the other hand, simply adds or subtracts ambient air to the suspension bladders. And with air comes...moisture. Although the Mercedes (Bosch, really) system includes an air filter, a denatured alcohol reservoir for absorbing moisture, and a purgable holding tank for expelling residual moisture that gets into the system, these safeguards are all things that tended to get neglected once these cars got beyond their original owners and regular Mercedes service. And then the valves start leaking, and the system (and perhaps the whole car) is either abandoned or quantities of money must be spent to makee it right.
Although requiring somewhat more attention than the hydroneumatic system, I submit that the air suspension system is inherently of sound design. My current 4.5 300SEL's valves were rebuilt about 10 years ago (its almost always one or more of the valves, not the air compressor), and it continues to stay up almost indefinitely. And one ride in a properly fetted 109 as compared to a steel sprung 108 will likely convince you that preserving that system is well worth the trouble. You can't enjoy the exhilarating performance of a 6.3 version of the 109 sedan very often, but the suspension of any one of the 109s will be a joy every time, all the time.
P.S. in 1972 4.5 a 109 cost about $2,500 more than a comparably equipped 108 (280SEL), and most of that difference was in the suspension!

I have the chance of finally driving my 109 after I had it in 'service' for a couple years. One reason was the car was going down in no time and I was deciding to renovate the air suspension on my own as I couldn't afford rebuilding from the suspected shops. This was an Odyssey but after 3 years of research and trying... finally I was successful and the ride is just perfect ever since the car was on the road. I claim to having solved the riddles and mysteries called 109 air suspension and I have built all tools and testing equipment. I as thinking to offer to forum members to renovate their leveling valve units and I am happy to discuss the system if there is any interest.
In the beginning I was close to convert the air suspension but I am happy today that I did not. The ride is exceptional and the system is beautiful... if it works as designed.

Martin

I wonder where all the 109 drivers are?

Or the W112 and W100 drivers!
Any 112s and 600s here?

The attrition rate on these cars after 40+ years must be substantial, and restoring any of the 109s, except for the renouned 6.3 version, is simply not economically reasonable. It's a labor of love, and there just aren't that many people who are willing to go into an economic hole to save one of these cars.
Of course, many of us (me, for example) didn't know we were going into that hole when we started.....
Excepting the 6.3, I doubt if more than 5-10% of the 109s that were manufactured are still roadworthy, and maybe half of them are in really decent shape in all respects.
Total 109s built: 23,430, of which 6,526 were 6.3s, 9,483 were 3.5s, 2,533 were 4.5s, 2,519 were M130 2.8s, and 2,369 were M189 3.00s.

WOW! Good story, Nice collection. I have loved the sedans, and wonder why there isn't more interest?

NONE of these cars are 'economical'. They are just beautiful and fun.
Did you ever fall in love? ...Yes, perhaps..... Was it economical?
What a question.

It wasn't the marriage that wasn't economical. It was the children.

I'm a fan of the air suspension Benzes too. I've had several including 109's and 112 coupes over the years. I don't disagree with anything already mentioned in this thread. My one complaint has always been focused on the cost of the parts associated with maintaining a properly functioning air suspension system. This really has nothing to do with the cars themselves . The cars are fantastic . I was hooked after reviving a neglected 300 SEL ,3.5 sedan.

A quick way to find a leak in the air suspension is to get your hands on an old A/C sniffer, which you can easily find on Ebay, and toss in a car of R-134 through the air tank under the front fender.

You might have to build your own hose to make this connection, but after you charge the system with a can of R-134 you can use the sniffer to detect even the tiniest leak.

Mercedes told their techs to never do this, but a lot of them did anyway. I learned this trick from an old tech that used it a lot back in the 70's.

I agree, the parts of the air suspension are expensive and hard to find. There is not a huge market and there is not much information out.
But the MB air suspension in its engineering is superb and the rid in a classic MB air spring car is priceless.

So it is coming down to the repairs of these cars and this is the tricky part:
analysis and find the appropriate/reasonable way to repair the system so you can enjoy the ride.
I went the hard way (well I was trained at Maybach and MB in Germany and I am an engineer) and it took me 3 years to repair the system without buying anything from the major suppliers (except for the new rubber air springs).
However this is a hard way to get to the result. The result was great and the car stays up for 1/2 year or longer...and it works to specs.

I will publish an article about the air suspension soon based on my understanding of the MB air suspension. And I will open a web site for information and maybe offer help or even rebuilding level control valve.

For the sniffing of the leaks with refrigerant.... you should expose the system for only very short time with the refrigerant...don't leave the refrigerant in the system for long as it is not in harmony with the materials.
MB was even proposed this method in the beginning (older service manuals) but withdrew for certain reasons... exhausting green house gases in the atmosphere is illegal. Use soapy water that creates bubbles and find the leaks with this method is doable.
In my article I am touching on the analysis which can be difficult.
But if you understand the principles of system better you will find it easy to find and interpret the leaks and do the correct repairs.
A big portion of the difficulties is understanding the system. It is a complex system indeed.
Martin

I couldn't agree more. The method I was suggesting was used by techs back in the late 60's and early 70's as time is money and the faster they could find the leak the more cash they could make in a day.

I troubleshot the system on my 6.3 and didn't find it that difficult. Different to be sure, but then a lot of Mercedes stuff is because it is better. Not just better made but better engineered.

It takes awhile for a person to wrap their head around the system, but then it is just a repair job. Your future web site will help owners of these systems because while they can be switched over to shocks the real question is why?

Mercedes W109 Air Suspension Part 5: Rebuilding the Leveling Valves - YouTube

Nice work on the video, Martin! I'm going to have to upgrade my garage attire, clearly.

Very impressive indeed, Martin. Fortunately my system was properly renovated back in 1997 before I bought it, and still works properly. But it's nice to know that you are doing this work should I have any problems in the future.

P.S. How long should I expect these valves (or more accurately, the rubber seals), to last? I'm now at 16 years and counting...

The magic question: how long? 16years...well time is up.
No...this depends on many things:
- was the unit renovated with fresh rubber or was it not...I mean NOS?
-How well is the rubber embedded in silicone or synthetic grease
- Is the car in use regularly (this helps!)
Typical life span of rubber seal rings inside is roughly 15 years.
Some hold up better than others. You might be lucky...still.
Keep the car going and good luck.
If it fails you know what to do.
Martin