W109 - 1971 300SEL Air Suspension Leaking

[Baxterdown]

Hi guys,

My buddy's 1971 300SEL's air suspension is leaking (the car collapses when it's parked). The mechanic is having a hard time finding the source. Are there any typical spots where these air suspensions leak that we could look for?

Thanks!

Jose

[berfinroy]

Yes. The leveling control valves and the main valve. These valves are almost always the source of leaks. There are 2 valves for the independent front suspension and one for the rear. The main valve is readily visible on the left (driver's side) inner fender wall.
To test, the car must remain on its suspension. Therefore you will need a "non-frame" lift for the leveling valves. soapy water should do the trick. Sounds like you have a bad leak if the suspension collapses overnight.
Valves are all rebuildable, but expensive. Star Motors, Endicot, NY for one. You might want to contact (Martin) "werminghausen" on this forum who rebuilds them independently.
If your mechanic is unfamiliar with this system, you would be well advised to find one who is. See also postings on youtube by a guy who describes the delicate proceedure for removing these valves without damaging the fragile tubing attached to them.
Lastly, some people have removed the system entirely and replace with components from the 280 series rather than going to the considerable expense of restoring the air system. If the rest of your friend's car is not in very good shape, that's a viable option, but take it from one who knows, a properly functioning air suspension is vastly superior, and once properly sorted, should give years of reliable service.

[alabbasi]

Put it up on a 4 post lift and use soapy water to look for a leak.

[68_280SE]

The valves can also leak internally and that would never show up with the soapy water test. If they are leaking down internally due to failed seals on the check valves or the STK lever, then the only option is to have them rebuilt.

John

[alabbasi]

Start with the basics and test for external leaks with soapy water.

[68_280SE]

Along with using soapy water to check for external leaks, there is an easy test you can do to check for internal leaking exhaust check valves. Find the master valve on the left fender. There is a rubber hose that runs from the master valve to the alcohol dryer bottle. Disconnect the rubber hose from the dryer bottle and place it in a jar of water. If you see any air bubbles then it is highly likely that the internal exhaust valves are leaking. I would make sure the car is a full height and was sitting at a rest position for 15-20 min before performing this test. I am attaching a picture right of the Mercedes shop manual as an example.

John

[Baxterdown]

Guys, thanks for all of your replies. And 68280SE, thanks for the manual pic!

We took the car to a vintage MB specialist who determined the main valve is bad and needs to be replaced. I found one re-manufactured on Fleabay by a company called Star Motors in Endicott, NY (Home - Star Motors NY - Star Motors NY - Star Motors NY).

They want $995-$200 core. ($795 final price).

Has anyone heard of them? Any other recommendations?

Thanks!

Jose

[JMela]

Star's a known shop with a generally positive rep but Werminghausen's outfit has rebuilt valves for less. Might be worth reaching out:

600AirSuspension

[Baxterdown]

Thanks JMela! From what's on his site, Werminghausen's prices are definitely less expensive. I emailed him already. I'll keep you guys posted.

[werminghausen]

Hi Jose, I emailed you back.

These air suspension components can be rebuilt to original spec. This is not easy but I am doing exactly that and I have done many 600s and 109 and lately the old style VNBs.
I am doing it because I love these cars and old systems. They work like an old Swiss watch.

It is often not easy to find out what the exact problems are especially when the system is still in the car and you don't know exactly what is going on inside the system.
For the people interested in analysis I am happy to assist if you have questions.
For basic information just look at the website for articles and some videos.

Best, Martin

[Baxterdown]

Martin, it was a pleasure speaking with you on the phone. Parts on their way to you on Monday!