2.5td Brief Hydraulic History

Detention doesn't worry me!

But back to the subject at hand, I must check the front ride height this weekend if it doesn't snow, it looks right but I've never checked it. I'm now wiggling in earnest.

BTW did I mention my greek in laws....

Steve.

Steve

Greek inlaws?? Are they anything like the ones in "My big fat Greek wedding" This means you espoused a Greek girl? So you must already know *very well* that Greeks are the source of anything good and civilised on this planet, and that all other nations owe them pretty much everything etc etc, don't you? My Spanish/Basque girlfriend already knows it!! She was a hard nut in the beginning but I finally convinced her Oh my, my, hope u r still keeping your humour....

Back to topic. You wrote: I was pretty thorough in cleaning the hydractive blocks, I stripped them as far as I could, everything out except the pressed in ball bearing and the parts behind the rolled pin (I couldn't get them out!).

Steve, u r great. This had been for me the last obscure point of the hydractive as I could not understand how exactly this mechanism functions. So I went looking yesterday various photos and schemas of HII hydractive blocks I have:



In the beggining I thought "something weird is going on". I thought this "pressed-in ball" can only be the ball that is in the middle of the 2nd crossflow channel, and also used for height correction when suspension is in "hard". The thing that baffled me is that, as I see from actual photos, this ball is exposed in the open air (isn't it?). Still in theory LHM passes around it all the time. I could understand at all:



Well, thanks to the document I attach I finally got it. Look below (photo No19 in doc): with damper "buttons" removed, u can see on the bottom right the main LHM channel, blocked by the hydractive piston in this instance (so it should go if it's in "hard").



Once this channel blocked (and middle sphere in same time, look other photos), LHM can STILL crossflow between left-right side (ie left-right corner spheres) from the hole at the top left. This hole goes round the block and ends at the exact opposite side, putting left-right spheres into communication. So actually, in HII (and NOT in HI with 1 hydractive block) this 2nd channel makes that the corner spherer are still in communication even when suspension ECU has put car into "hard". So on the straight line car is not so hard as an HI, where corner spheres are totally isolated when in "hard" mode. It is softer because when one wheel meets an object, the other side sphere also participates in absorbing it.

However when cornering, the HII car would tend to roll more due to this arrangement. This is where the little ball comes into play:



When car rolls e.g. to the left, the LHM flow will tend to move the ball towards the right, and eventually stick it to the LHM passage, stopping the crossflow from left to right and thus reducing roll, which will now only depend on the left sphere's pressure and damping. Well, this ball is actually NOT the visible pressed-in ball (photo No4) !!!! Rather, the real "roll control ball" lies deep in the block, behind the "rolled pin" that you couldn't remove Steve! What is happening is explained in Photo No32. The parts beneath the "rolled pin" are the 3 depicted: a plug, a piston and a spring:



In photo No33 you can actually glimpse the "roll control ball" deep inside, once those 3 parts removed:



So this is actually how it works: when car is IN SOFT mode, the LHM for height change is being administered/extracted through the main crossflow channel. When the middle sphere is out this channel is blocked. If u ask for a height change, the system pressure not finding another soft point, will press the springed piston which will then press the "roll control ball" and force it in the middle of its "room", leaving LHM to pass (it comes in/out from between the "plug" and the springed piston's head). This feature with the springed piston is there only for the purpose of ensuring height change when car is otherwise in hard. It is not doing any other job.

However the interesting bit related to suspension softness etc is the "roll control ball" and the tiny "room" it has to wiggle. I believe this point is be one of the most prone to clogging up in the system. LHM does not flow through it when car is in soft mode AND going in a straight line -i.e. daily motorway driving for most people in the UK-. This passage only feels significant LHM flow when the car is ROLLING, in soft or hard. Also when it takes bumps/holes from one side only. This point being clogged up would remove about HALF of your suspension's ability to absorb shocks in SOFT -as you can see the hole size is pretty much similar to the other "main" LHM flow channel (photo19)-. They are damped from the same shared "button" damper. When going in soft, on a straight line, and 1 wheel meets a bump, e.g. the left wheel in photo below, the volume of displaced LHM rushes towards the other side through these 2 passages. There, it pushes the middle sphere and also the other corner sphere, with equal pressure:



This cross-flow function, present in the basic hydropneumatic systems also, provides "half the softness" of the suspension: it makes for reducing the antiroll bar's tendency to amplify the size of the motion (by withstanding its pressure on the opposite side wheel with a pressure exactly equal to the pressure it receives from the bump at the other side!). This makes the 2 wheels tending to move in OPPOSED directions each time, while in cars with spring coils, the antiroll bar AMPLIFIES the shacking by tending to move wheels in the SAME direction -stupid suspensions...-. This could partially explain why HII cars are noted (from me and others) to be very "crashy" when ONE wheel meets a bump while being relatively more comfortable when BOTH wheels meet a speed hump or so: the crossflow effect is not functioning to its maximum if this passage is blocked!!!! This was the case in mine even when I had fresh comfort spheres at the corners!

Alright, that's one thing. The other GOOD NEWS is that, having understood the difference in height-correction function between SOFT and HARD modes, I now see a much more effective way of cleaning up this sensitive spot: put the car electrically in "hard" (just remove the relevant ECU fuse) and start ups-downs!! All your flushing liquid will pass through and only throught this channel and make it see flow that it has not seen for ages!!!!

Ok I'm off to get started!

cheers
George

ps. as for the visible big pressed-in ball, I still don't know what it's doing. The author of the document attached says it's just a blanking ball for the hydractive piston...

This post has been edited by jorgy9 on March 19, 2008 01:07 pm

George, do you work with hydraulics, or just spend a LOT of time pondering the hydractive set-up? Your knowledge of the system must be passing that of some of the Citroen engineers by now Well done.

I now know what I will be doing next to help clean my system. Unfortunately I have had a leak somewhere, so have been a bit reluctant to do the ups-downs as it tends to drop fluid when I do. Once I have tracked down the offending perished pipe I will be doing so in hard mode more often.

Hi George,

Nice work there. I'll need more time to digest it though, my brains a bit frazzled at the moment.

I did hope that by removing the pin I would be able to extract the 'plug' using a strong magnetic probe. That didn't work so I gently heated up the block fully expecting there would be seals inside that could be damaged if I took it too far but that didn't work either so into the ultrasonic cleaner it went.

I'll be trying out your suggestions asap!

Do you think you can improve your suspension further?

I've never seen the film so I don't know, maybe one day I'll watch it. I do have Greek in laws but only by marriage. My wife's sister married a Greek guy. Yes I agree, they are basis of much of civilization. In fact at times it's embarrassing to see how the British behave and think of the Greeks. They still have much to teach us when it comes to respect and family. I've been to the 'christening' of my niece and nephew which was great. We go at least once a year to visit which is lovely because they own their own hotel. Lucky eh? As for all things great I do have quite a fondness for their cooking!

As for humor, no problem.

Steve.

So how about a bit of driving in electrically induced hard mode, would that help at all?

I suppose that if you were really careful you could drill and extract the plug. I may try that on my spare to see if there is much gunk in that area.

Steve.

Hey Rowan, no I'm an economist etc. by training, but yes, I'm DETERMINED to make it work! Plus, on the way I've been convinced it's worthwile. This hydraulic suspension is probably one of the few real great material-related revelations anybody can have in life. One of the cases that most make you wonder "but why on earth don't all cars have this system??".

It goes to show how simple -ingeniously, you have to admit- it really is when one not-very-clever person that didn't know what a "sphere" is back in 2004, can achieve full understanding just by...looking photos publicly availabe on the Net! Let ignorants mutter about how "complicated" and "unreliable" etc it is....

cheers
George

ps. Do you know, the whole hydropneumatic idea belongs to and was developed by Paul Mages, who was NOT a trained engineer, on his own initiative and free time in Citroen!!!!

Hmmm the author of the document does not mention how he extracted it. Perhaps I can email him and ask -it's Christophe Tattin, one of the pros I have to say of Citroen hydraulics+electronics, he writes in the French Activa yahoo list-.

I think the suspension will improve to the degree this point is clogged, simple as that. Taking into account that theory shows this point doesn't see much flow even when doing ups-downs, I think even on my car (almost 6,000k on flushing oils today) there will be space for improvement.

cheers
George

I think driving in hard wouldn't help because it doesn't provide the right flow direction to unclog things there. And, if it's already clogged, there will barely be any flow...just the corner spheres working in isolation really.

Yes, it will be very interesting to get a "weathered" one open and see its state! On the other hand, you ARE aware that a hydractive block goes for £300+ from Cit nowadays...

Is yours rusty and stuck like the one in my photo? I think it'd be only that rust holding it from coming out with the magnetic probe?

cheers
George

Hehe, most people show horror when I tell them that, in christening, we still throw the whole baby right into that big bucket of oiled water, baby crying its brains out But what do you want, that's how you get tough Spartans afterwards

Hey if u ever up to Scotland I should cook some nice stuff for you! Yes, after 5 years of self-training I'm now a fairly good cook -my Spanish girfriend loves it, at least-. In fact we should organise a Scottish-based meet in my place and work on our Cits prior to terminally indulging into the barbecue and other goodies I'll have prepared! But this will have to wait till I write up and submit my thesis -which is not about Citroens, unfortunatelly -. Hey, we'll all be still around no doubt!

cheers
George

This post has been edited by jorgy9 on March 19, 2008 06:13 pm

Just out of interest. What are the hydractive blocks like to get out? Do I still have to un-sieze those silly little pipe fittings from the ends?

Hi demag

The front is very accessible from underneath the car. You'd have to unbolt the 2 thick hydractive pipes coming in, and then the 2 high pressure pipes as in photo -these are better done with thin hands, if u know what I mean-. That's all. The whole thing is held on its bracket by 3 easy bolt-screws.

The rear is same but is hidden behind much stuff...

cheers
G

I'm not really sure why it was stuck, I just assumed corrosion was the reason hence the gentle heating.

I'm not surprised by the price of the Hydractive block, the Electrovalve a pricey part too. Luckily I picked up a few spares a couple of years ago for my Xantia and it happened to include a full Hydractive block (also got a 6+2 pump, regulator, anti sink valve and a few other connectors/valves).

I was thinking that If I put the car in hard mode electronically I could exercise it whenever stood in a line of traffic, etc.

The 'christenings' are quite a celebration aren't they? We had a great time. One or two of the British commented about the dipping and how it made Andoni cry but my attitude was it's his right of passage and his culture, his sister Anastacia didn't bat an eyelid.

As for the food where do you start? My favourite is Stefado. That said I'm quite keen on goat meat. Maybe I'll make that BBQ.

Hope the thesis goes well!

Steve.

Hey Steve, here's the answer to the above...

http://club-xm.com/forum/index.php?showtopic=3072&st=50

I thought we better not abuse Demag's thread more (Sorry demag!), this should be really a thread where he describes the developments in his car!

cheers
George

This post has been edited by jorgy9 on March 20, 2008 04:06 pm

About time too!!

To be honest George it is all relevant stuff though isn't it. Everyone posting on this thread has similar problems and we're all looking for that elusive answer.

Easter's looking a bit damp dark and cold though for any work.

Steve - stuck plug in hydractive block

Christophe Tatin has answered me from Activa list that he doesn't remember how he extracted this piece so he assumes it was not any difficult to do. From what I see in his document's photos, the external condition of his block was not rusted, so unless your block is rusted externally, then it can only be that this piece is stuck from within -which may say something about what's the situation in there?-. Let's see...

cheers
George