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The Citroen Hydropneumatic Suspension - of Headphones. The $299 N90Q

Frank Dernie

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The current Range Rover suspension uses air as a "spring" and can be tuned to allow variable rebound rates to feel sportier or softer on various road surfaces. It uses a fairly complicated feedback mechanism to control air pressure at a distribution block. It's inflated by a glorified bicycle tire pump.

The weakness of the system is the air bladders at the top of each strut. Rubber tough enough to hold pressure can be stiff and will develop fine fractures with age - leading to failures.

My own (dearly departed) A8L had a similar system and the VW parts bin controller was temperamental, prone to locking up at full height and unserviceable by local repair shops due to its model year and computing requirements.

The Citroën Hydropneumatic suspension was 50 years ahead of its time, using mineral oil as the incompressible fluid. Early versions suffered corrosion failure when standard brake fluid was substituted.

This system required the disruptive spherical reservoirs that held Nitrogen in half the chamber separated by a membrane from the mineral oil.
This dampened the system on uneven pavement.

Mercedes Benz used a similar design in their Self levelling system.

Later Citroen versions called "Hydractive" employed more complex computer controls but the earlier versions were mechanical wonders.

It was robust, supple and flexible. It was purely mechanical, with no electronic monitoring or control valves.

Poor dealer service support doomed the brand in North America, often due
There was a lot clever about the Citroen system, which I got to know quite well.
One of the things I liked best was that the power brakes - rare in Europe at the time - had a 2 way proportional valve system. The valve for the front brakes was fed by pressure from the main system. The valve for the rear brakes was fed by the pressure in the rear self levelling circuit so the brake balance altered with rear load. Genius!
 

bloodshoteyed

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do they leak LHM?

the brakes, right....what a weird feeling it was on the pedal
and in case there was a system failure, you lost those, too (at least until the hydractive 2 i think, where it got de-coupled from the main system)
haven't had any major issues on any of my 3 hydros, tho (besides the electronic glitches and sensor failures on the c5 mk3 and an obnoxiously loud mainpump)
 

Wes

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somebody post a Citroen homage thread and I'll round up some videos for it
 
OP
Cahudson42

Cahudson42

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Even the great Elon Musk is apparently ignorant of Citreon hydropneumatic system many advantages..Correct?
 

sofastreamer

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Sorry die beeing late to the party, but I do not get the mentioned price tag of 299 . afaik the n90q cost something around 1.200 EUR back in 2017. Could some please help, what the TO is referring to?
 

MayaTlab

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Sorry die beeing late to the party, but I do not get the mentioned price tag of 299 . afaik the n90q cost something around 1.200 EUR back in 2017. Could some please help, what the TO is referring to?

It's occasionally been promoted at such a stupidly low price on AKG's US website, that's all. It's now back to its normal price.
in France you can get new ones for €599.
 

TrevC

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That suspension was horribly unreliable, I had a friend with one of those fancy Citroens and there was no end to his car troubles.

The headphones are interesting though.
I had a C5 Exclusive Estate for 11 years and nothing went wrong with the suspension at all, not even the spheres. A lot of garages have a weird phobia about them, but servicing the suspension on the later cars is really quite easy and simple.
 
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Loathecliff

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However I do have that vivid memory - of each older Citroen DS parked on a street ’facing upward’ due to failed suspension.
Ten months on before I notice this utter nonsense. A parked one has failed suspension?? You deduce that because it's sitting low? :facepalm:
 

FrantzM

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Ten months on before I notice this utter nonsense. A parked one has failed suspension?? You deduce that because it's sitting low? :facepalm:
Me too! The DS21 was our ( a cousin and I) dream car. Never owned one.. He did.

Peace.
 

Raindog123

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Ten months on before I notice this utter nonsense. A parked one has failed suspension?? You deduce that because it's sitting low? :facepalm:

No, because _the butt_ was sitting low — literally touching the pavement. While the iconic front was facing the skies — locked at the highest point. Visually very odd, and I bet inconvenient for the passengers too.

Fully agree, utter nonsense! :)

And again, witnessed it multiple times — in Paris, in Amsterdam, and in-between... My friend’s dad actually had one with such an issue - I rode in it once in Paris in 1992, when the dad came to pick us at the Gare du Nord. Interestingly, in motion, the car would level itself fine…. And now as I think about it, the craziest part of the story is that my friend was a mechanical engineer working for PSA Peugeot Citroen Group designing suspensions!
 
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