How to test the suspension on a 450 SEL 6.9

I am interested in buying a 450 SEL 6.9 (European car). However the car has been sitting for quite some time (a few months); in the very beginning when the car was for sale I already mentioned that the front
of the car went down first meaning probably that the front valve of the suspension s leaking?
I would like to go for a test drive but how do I check the suspension? The car is sitting now in his lowest position but when it will be started it will raise completely I suppose. How do I check now if the suspension is working well without having to wait for a few days to let the car sink down?
Regards, Kris
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@advalvas.be (kris) haute in die Tasten:

IIRC the 450 SEL 6.9 uses a hydro-pneumatic suspension (HP) under license by Citroen. Unfortunately Mercedes only took the HP license, but decided to make the HP parts on his own, while other manufacturers like Rolls Royce/Bentley used straight Citroen parts. So spare parts for the Mercedes HP as well as mechanics skilled to do maintenance and repair to the Mercedes HP will be quite hard to find.
Unfortunately I have never driven a 6.9 with HP, but I own a Citroen Xantia with HP, so perhaps my remarks may be useful for you.
The main sources of trouble are these:
1. damaged suspension spheres: The HP uses spheres, which are about the size of a big fist. These spheres are filled with high pressurized nitrogen (pressure depends on the type of the car but can easily be as high as 75 bars, which is 75 times the normal pressure of the air you breathe or about 25 times the pressure of a car tire). These spheres also contain a membrane, which separates the nitrogen from the HP fluid (HPF) The system works in that way, that a pump presses as much HP into the system that the car stands at a good level. The suspension work is made by the nitrogen reservoirs in the spheres. These spheres tend to lose pressure over the years, besides that the membrane will wear out and lose flexibilty. If the membrane is not damaged, a flat sphere may be able to be re-pressurized, but this requires special tools. On most Citroens the spheres are not supposed to be refilled, instead of that you simply throw them out and replace them with new ones (like you would chage shocks). One usual Citroen sphere costs about 60-80 USD, the change is quite easy. The Mercedes spheres may be different, hard to get and more expensive. Citroen spheres have a life span of 60.000 to 100.000 miles. I suppose that the Mecedes HP system does only the suspension job. On some Citroens the HP does also support the braking and the steering, so these cars have up to nine spheres. A 6.9 probably will have only 4 of them.
2. not enough/dirty HPF: Use only the fluid which is cleared by Mercedes for that car. Do not use motor oil or ATF for that job. This may damage the seals in the system. Maybe you can find out how the colour of the Mercedes HPF is. Citroen HPF is bright green, and if the fluid in the car looks dark brown, you know that it is due for a change. If the car has been sitting very long and there is a lot of dirt in the system, Citroen offers the opportunity to replace the usual HP with a rinsing liquid. You drive the car for a few hundred miles with that fluid and put in fresh HPF, and the system is clean again. There are also several filters in the HP system, which may be required to check and clean.
3. worn out or stuck height level correctors: Most Citroens have mechanical devices to detect the level of the body over the front and the rear axle in order to provide a defined ground clearance and an even body level, no matter how many people are sitting in the car and how much luggage is put into the trunk. These mechanical devices can get dirty and rusty. A worn or stuck level corrector will result in a car which is too high or too low and does not ride softly.
4. leaks in the HP tube system, leaking seals. After you have looked after the colour of the HPF in the car, you should carefully inspect the car for leaks.
5. damaged HP pump. If this pump is worn out, the car will not hold its level.
When inspecting the car, I would suggest the following:
1. Have the owner start the car and leave the engine in idle. Gear lever to park, park brake loose. Stay outsides and carefully watch the car. It should rise within 20 seconds to normal level, and it should do that softly. If the car sits on the ground and suddenly the back pops up, something may be stuck there.
2. If the car is up, leave the engine running and press down the body by hand on each corner of the car. You should be able to push down the body by 5 or 6 inches quite easily, and the body should come up again softly after that. If you cannot push down the body, something is stuck.
3. If the car has a lever for adjusting the ground clearance, test it (all HP citroens have such a lever). The car should change its level smoothly.
4. Have a test ride. The car should run smoothly as silk, you should feel like on a cloud. If the car runs hard instad, then one or more of the spheres are damaged.
5. after the test drive, leave the car in park, switch off engine. After some 20 seconds, the ar should sink down by two or three inches. This is usual and nothing to worry about. If the car does not sink at all, or if it only sinks on one axle, while the other axle stays up, something may be stuck.
6. carefully inspect the car for leaks
7. ask the owner for proofs of services made. Ask him how old the spheres are and wether he has changed them or not.
When Mercedes developed the W140 S-class, they took a Citroen XM for suspension benchmarking. His successor got air suspension. So you may expect an extraordinary riding comfort.
Frank
--
please replace spam-muelleimer with fk-newsgroups for e-mail contact

Citroen - Made in Trance
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wow... that's some info you got there!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
As someone who has 'regular' suspension I am thinking of using the info for bedside reading...when I have insomia...
:-))) DAS
--
For direct contact replace nospam with schmetterling
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
...insomNia, even...
Grrr, can't spell anymore... DAS
--
For direct contact replace nospam with schmetterling
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
1) stiff ride-spheres are shot, replace 2) leaking struts, replace or have rebuilt 3) valve, may leak internally, car will usually ride fine but go down over time 4) pump-pressure test, it can be rebuilt
Its a very simple system.
at 03:10 AM, snipped-for-privacy@advalvas.be (kris) said:

--
-----------------------------------------------------------
Fred Emmerich
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.