Hydraflush And "hydronet 2000", ...and the happy ending of an Odyssey!

What I note in the morning start is hydraulics are "tighter": the pressure regulator clicks many times to get the car up, which means it "sees" many times a pressure of 170 bar. Later in the day it will go from bottom to highest with the regulator just clicking once, at the end of the travel. Couldn't say if it's colder LHM, or colder strut cylinders, or both...I know though that for extremely low temperatures Citroen recommends using hydraflush permanently.

I also noted a clear firming up of the car now that I've reverted from hyraflush to LHM.

G

Hi Jorgy

How much firmer?? not too bad i hope. Mine is still on hydraflush, but while I'm doing major works at the moment i changed the fluid again, this time there was a black/brown coating on everything in the reservoir and a little muck in the return filter, but not clogged up like the first time i changed the hydraflush.
I have rebuilt the spare FDV with the kit from Citroen but i have a small 'O' ring left, couldn't find where it went though, and they give you double rations of pipe seals, which will come in handy .
When my man flu goes i can get out and working on it again

Dean

It's not simply firmer in the sense of "less comfortable", it's kind of different, I think it's more like the feeling I had in the "soft day" of 2006: the car feels totally inert, ie it feels very parallel to the road at all times, it corners flat, you can throw it for fun without danger, you just cannot upset it, how can I say it. The first times I drove it I sometimes got the impression it was also worse in absorbing the smaller stuff, but as I know air can have this effect, I din't report much, I'll do so in a couple of weeks when any air will have self-bled from the system, have not driven it much since. Just the rear made me sad because clearly it has reverted back to its "not perfect" state, while prior to feeling up LHM it had totally unstuck just after me doing the up/down thing in hard mode -but didn't get to drive it to confirm, next day I found the leak-.

So will final impressions later on how exactly it is on LHM.

G

Reading in between the lines on all these posts it would appear everyone is happy running on hydraflush but everyone has issues of some sort running on lhm. So why not just run on hydraflush?

I was looking at the GSF sphere table last night and noticed one Xantia model runs rear spheres same spec as the Xm but the centre orifice is larger. As I still have to change my rear wheel spheres would anyone like to comment on suitability? I do like a softer ride. Although my suspension is better now than any time since I had the car it is still very joggly and crashy especially over pot holes.

Hi Dave

Unfortunatly hydropnumatic suspension is joggly over pot holes, at low speeds, its a characteristic, anyway, the tyres are the main denfence against that. If you can find some with more pliant construction it will help with the low speed irritation. The pressure also makes a lot of difference, you will find that the ride improves with time but that is only because your tyres are going down.

I run mine at slightly under the reccomended pressure and that makes quite a difference - I wouldn't of course reccommend that you do!

Regarding the Xantia spheres, the orifice on the XM comfort spheres is noticably larger that standard but not massively. It is still very small compared with the non hydractive variety but probably only about .5mm larger than normal.

Peter.N.

Hi

Demag if u r sure they are same spec on volume+pressure then why not go for them. This said, do you know the state of your current rear spheres? If they are just too low on pressure, you would discover that standard XM specs will just be great, the rear on Cits normally feels *ridiculously* soft compared to the front when there are no rear passengers (because, thanks to the height+spring rate adjustment system, it just doesn't need to be harder if there's no load at the rear!) -and it's 100% normal it's joggly now-. Whatever you do though, better don't delay it, the most variables you get to move to the "fixed" area, the faster the process...

Peter, once again, I can only disagree with this, my car, especially the front which is 99% sorted, is *not* crashy anymore on potholes or anything else similar, at any speed. It *had* been crashy in those instances, even when I had comfort spheres on, while on the motorway it was wallowing like a boat and it was obviously very soft on pushing it down by hand. So the crashiness in the XM on medium or large depth holes is a fault. I have played with tyre pressures and in my case I remember once lately the car was suddenly behaving bad and I found the front pressures were a bit down, around 28 instead of 32-33. Some day in the past, when it was still crashy, I suddenly felt unbelievable comfort and entered the next petrol station on my way to find the fronts to be down to 14...Now I tend to try keep pressures where Cit specified them, to "know my onions" (or how do u say it...) I wish I could give u my car to drive to see for yourself....

The only instance where mine was lately still "weird" (not "crashy") was at points where the tarmac is severely rough (not rare on Brittish roads) or very patchily broken, like in photos below.








BELOW, MY CAR WILL PASS THE HOLES FINE BUT WILL BE NOISY AND TRANSMIT HIGH FREQUENCY VIBRATION WHERE THE TARMAC IS LIKE THE RED-CIRCLED ONE:




Passing over these gave you the feeling the suspension "has frozen" and road noise increases alot, to ubnormal levels for any sort of car. As with the crashiness on bigger obstacles, and the inability to absorb smaller obstacles, I have concluded this was again all down to how quickly the struts could move, how "sensitive" they are. There is such a patch of motorway -about 100 yards- that I pass every day and is a great test for this sort of "noisy" behavior. Let me tell you, as the miles added up on hydraflush, the car tackled it better and better and today you almost don't realise there is such a piece of road under your wheels. This sort of "incompetence", in my experience, is the last symptom that will be erased as your suspension is being cleaned up from hydraflush. All down to strut sensitivity, that has been gained back. Note that, as this suspension operates in practice on a few mms of movement for absorbing a bump/hole the height of a few centimeters -it's a high precision mechanism- every component has to be totally friction free and up to scratch -cylinders first-.

+ I actually still consider this detail to be abnormal, fact is I do not remember *any* weird impression on the one day the car was excellent, just *nothing* to think from the suspension side, I would have noticed it, wouldn't I ?

cheers
George

This post has been edited by jorgy9 on April 04, 2008 08:20 pm

I agree with Peter N, the very nature of the hydropneumatic suspension does not have the response time to absorb short,sharp inputs.The electrovalve is powered open for the very purpose of initiating as rapid a response as possible Typically the opening time for the valves is 100ms (due to the inductive effect of the coil causing the current to rise slowly) whereas the closure (the rapid collapse of the magnetic field)is done by removing the supply current, typically 3-10 ms .Logically it is more important to change to firm mode more rapidly than the return to normal mode hence the reason for feeling these high frequency inputs.

Hi Robert

not sure I understand your reasoning there, my suspension is in "soft" during going over all these surfaces, i.e. electrovalve is electrically active and hydractive piston is open -no hard mode involved- ??

I have also read the typical comments on hydropneumatics on various road-tests of new cars (tramlines etc) however

1/from my own experience and only, I suspect this has been largely corrected in the Hydractives; further, I personally encounter two (2) single points in my 40-mile daily trip where the car behaves similar to that description. They are in the city of Glasgow, one is tarmac as in photos that has been broken from recent bad weather, the other is a not-so-well applied piece of tarmac that gives a train-line pattern to the road -as if one had done parallel lines in the sand with his fingers-. This would make it 2 out of what, say, 500 total "bumps" where I get a "disturbance". This is OK. As for the "noise" in rough tarmac, I suspect this is also down to tired bushes (strut top rubber, 4 bushes of rear subframe), so don't expect it to go completely away till I renew those.

2/from Peter's descriptions and others' (not only in this thread) I can recognise the symptoms I had which is something different than (1/). "One single wheel falling in a hole and crashing, especially at the moment of return" is not normal, even more so if this is happens many times a day in your daily drive.

Surely there must be someone out there who has driven his XM from new and can add his opinion here rather than us trying to make sense out of a mess -comparing old cars with totally different maintenance profiles-???

I'll say this again though, from my experience: if you are not extra-happy with ur XM's comfort, if many times a day it makes you think "that's not as good as I expect it to be", then rest sure your suspension has issues.

cheers
George

This post has been edited by jorgy9 on April 04, 2008 07:58 pm

Hi George. my reasoning was theorised on the ability of the body movement sensor to detect these high frequency shocks and so switch to firm mode quickly,therfore the pressure pulse generated(the actual quantity of fluid displaced is very small) in the fluid can only be absorbed by the corner spheres.

Ah, right. I'd think this sensor could not be so sensitive, but worthwhile checking it -with the radio- next time I drive over those points.
cheers
G

Hi George, the body sensor - if my facts are right - will trigger the processor when either a displacement of 60mm occurs 3 times or more per second or a rate of change of 0.3mm per millisecond. The hold-off time is 0.4s - unless another change occurs (steering sensor etc) - plus the 0.1s for re-energising the valves, so all in all 1/2sec to switch back to normal mode, hence on broken surfaces the body sensor will likely continue to re- trigger well before the changeover time, holding the valves de-energised.To put the timescale into perspective the blink of an eye takes 15m/s!I think the the problem we are all stuggling with and trying to define is, is the suspension in the right mode? As an aside, i've read somewhere that replacing the hydractive sphere with an accumulator sphere there is an improvement to be had in comfort without detriment to overall performance of the hydractive system.

Hi Robert

So your hypothesis would be on the "rate of change of 0.3mm per millisecond" induced by rough/saggy tarmac, right? On Monday I ll drive the XM again and see if it goes in "hard" over those surfaces.

Don't know about the accu sphere in place of hydractive, could be, as they are similar, however odds show the accu sphere will be "harder" than a standard middle sphere for the front:

accu:
400cm, 62 bar

hydractives, front:
450, 75bar
or
500, 70 bar (depending on year)

At the rear an accu sphere would give a much softer feeling -too much perhaps- as it is same volume -for hatches, estates have 500cc- but much higher pressure, 62 vs 30 or 40bar (can't remember exactly).

Why experiment though since the car can be perfect if all gets to work like it was designed to...

E.g. I often wonder why Cit have specified the accu sphere to be *exactly* 62 bars (why not...60?) for all their models since hydropneumatics exist, well this must be the optimal for some reason...

cheers
George

Hi George,

Ref the accumulator pressure. Without doing the sums I would guess it's for the same reason that aircraft hydraulic accumulators always have air charging pressure of half the system pressure - it gives the maximum volume displacement between cut-out and cut-in of the control vave.

Derek

This post has been edited by DerekW on April 05, 2008 07:09 pm

Hi Derek

...makes sense, yeah. Putting the numbers down (145-170) it shows the accu sphere diaphragm would move in a range between a little above 50% and less that 70%, sounds ideal.

cheers
G

Sorry to hear you've got the 'lergy Dan, looks like you might get some snow tomorrow too. Stay in and warm, or get some fresh air or something! Just saw beeb forecast, if its any good then snow will miss me and I'll get to do the mirror and the hoovering on mine.

regards