Hydropneumatic Suspension - Part 1

[Styria]

I have been wanting to publish, or make available, the genuine workshop details about a subject much misunderstood, or we simply do not have the knowledge to get the system to work properly. Of course, it doesn't help if parts are no longer available, or alternatively, are priced at such levels that you really have to ask yourself as to how you can keep your car running.

There are sixty nine pages in total covering this section of the suspension, and in the interests of clarity and simplicity, I have divided the procedures into four sections. Therefore, Part 1 is a general introduction and explaining the principles of operation. Regards Styria

Part 1

 

[Styria]

Part 2 deals with the various suspension elements.

Part 3 concentrates on the pressure oil system

Part 4 hydropneumatic suspension details.

It can only be hoped that the details will be of interest, and to help us understand the system, and its complexities, a little more clearly. Regards Styria

 

[Oversize]

Definitely of interest! Thanks Styria!

 

[Oversize]

Interesting differences between the W116 and W126 systems.... I'm wondering how a W126 would handle with W116 gas cells??

 

[Helmet]

Interesting differences between the W116 and W126 systems.... I'm wondering how a W126 would handle with W116 gas cells??

The 116 cells have been superseded to a 126 part number

 

[Oversize]

The front and central cells on a 6.9 run at a higher pressure than the W126 ones (red vs green) so I doubt they have been superseded. The red cells were specified for the heavier M100 engine. The W126 with the lighter M117 engine has green cells for all 5.

Hence my question about how a W126 might behave running red 6.9 cells on the front? Would it be similar to the 'sport' struts that were once available?

I used to think a regular car's suspension was pretty simple to understand. The steel springs control the ride height depending on the weight involved and the shock absorbers control the movement of the spring in bump and rebound. However is gets more confusing with a progressive rate spring which changes tension as it's compressed.

A little like the cells in a hydro system which increase spring rate as they are compressed. I'd have thought this would reduce body roll over and above the standard 450, however the 6.9s stabiliser bar is actually bigger than a standard one! Perhaps it's simply due to the valving arrangement which might allow fluid to move from one side to another during cornering?

So what controls the bump and rebound on a 6.9, or a hydro W126? Is it only the struts, or a combination of both?? Clearly the factory mod was to replace standard struts with the sports ones if the owner desired. Being these are NLA and a mod to the standard struts is yet to be investigated, I'm wondering if cells running higher pressures could achieve the same result? Or if a mod to the hydro circuits could improve cornering stability....

 

[Helmet]

The 116 cells have been superseded to a 126 part number

The front and central cells on a 6.9 run at a higher pressure than the W126 ones (red vs green) so I doubt they have been superseded

So what controls the bump and rebound on a 6.9, or a hydro W126? Is it only the struts, or a combination of both...

Seriously ,they have been superseded,they do the same job, , when you say higher pressure where do you get specs for gas pressure in the cell ?

 

[Oversize]

Well that makes no sense unless they're only supplying high pressure cells; which would probably make the ride on a W126 harsher than normal. I don't have access to the EPC to clarify. I don't have access to my W116 book at the moment either but I've added some pix from the W126 Series 1 book. And it makes very interesting reading....









I was slightly incorrect; the W126 uses 4 green cells and one red (central) cell. I'm going by memory that the W116 uses 3 red cells (front and cetral) and 2 green (rear).

 

[c107]

On Citroens, where this system basically came from, each car specifies different spheres for front/rear and the cars ride like crap if you use the wrong ones.

Also, Safaris (wagons) have different rears to the Berline (sedan).

Its a shame the fittings are different as the throwaway spheres are cheap and the older ones are rebuild-able.

Interesting the spec on the scan there is almost identical to the DS front sphere which is 59.

For interest, the Citroen specs are:
DS Front: 59
DS rear: 26
Safari rear: 37
accumulator: 62
brake: 40

CX front: 75
CX rear: 35
Safari rear: 40

The big difference is Citroen's are heavily weight biased to the front.

I have no knowledge of the Mercedes ones, I have never had a full hydro Mercedes.

 

[Oversize]

For those that are old school 100 Bar = 1450PSI which is the pressure of some petrol powered water cleaners for removing graffitti & the like. Not something you want directed at you...

 

[Oversize]

This part is interesting because it compares the 116 & 126 cells. Even more interesting is it mentions blue dot cells on the rear of a 6.9. I'm guessing NLA since the pressure differences weren't that great.

 

[Oversize]

Here’s operation control from the driver seat…