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Full Version Xm Behaviour In Hard Mode

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Hello all,

I wasn't sure whether to post this here or in the "hydraulics" section, but Noz can decide on that I guess.

I'm generally disappointed by the way my XM's hydractive II suspension behaves when in hard mode. I don't say anything is wrong with it, it seems to work as it should. However, in hard mode the front behaves exactly like a car which is very hard springed but too soflty dumped. It pumps up and down with a force that seems unstoppable -mind you, it carries a V6 in front-.

This is of course very annoying in the city, but I'm most worried it could become dangerous on higher speeds as the car in hard tends to loose contact with the ground. Imagine taking a long, not tight curve at 70 on the motorway, the car is easily in hard for all that time and, if the tarmac is not exactly perfect, it pumps up and down in a manner that's just not correct...It'd be much safer just in soft mode.

Are your Hydractive 2 cars behaving the same or is it something with my car? I'm thinking I could possibly have the wrong damper valves on my front spheres?

Any experiences would be much appreciated.

Hi George,

There's potential for a few issues wrapped up in your symptoms. Here goes with some questions (in no particular order):

Can you feel a reasonably significant change between hard and soft ie how sure are you that its changing from one to another?

Have you any idea about the condition of your spheres, both the wheel ones and the centre hydractive ones? Do you know the age of them? Have you had them tested to find out how much pressure is left in them?

What makes you think you might have the wrong orifices fitted? Do you know some of the sphere's history which makes you believe this? Do you have 'comfort spheres' fitted? Maybe they allow more body roll than usual and therefore make the ecu go into hard mode and stay there longer.

Does the car sit too high or too low and therefore near the bumpstops?

There are several measured parameters which trigger the ecu to go into hard mode. Turning the steering wheel sharply, braking hard, cornering hard, accelerating hard etc. In each case there's a reason why you would want it to go into hard mode. During the time when your in hard mode the parameter which put it there is continuously checked. If the parameter returns to within its limits then hard mode is switched off again. This all takes place very very quickly. I would be surprised if the ecu kept the suspension in hard mode for long periods of time. On a long slow curve the only possible parameter that could be triggering the ecu is the sensor connected to the front anti roll bar to detect body roll. However, if the suspension is stiff then you shouldn't have any body roll.

Hard mode is, and should be, equivalent to sports car style suspension stiffness. Soft suspension is whats dangerous on corners not hard. Just compare big american jaloppies with water beds for suspension compared to a formula 1 car which has all the springiness of a stone slab. Which one corners the best? What you seem to be complaining about is a level of stiffness which would appear much harder than you would expect.

I suspect a number of possibilities in various permutations:

Flat spheres, wrong spheres (therefore wrong orifice size), blocked orifices within the electrovalve body, flat accumulator sphere.

Can you describe any of the above in more detail to try to narrow the problem down and possibly return your prized posession back into the rolling godess it should be?


noz cool.gif
Noz thank you very much for answering, that's important to me as I really appreciate all the car in all other respects.

Spheres have probably enough pressure in them and the car clearly operates both the electronic and hydraulic aspects of the soft/hard modes. As I said the car feels fairly good when in soft, with the -mentioned by others also- exemption of the harsh reactions when a single wheel hits some hole in the road. I have just added 2 new diodes on the ECU PCB so definitely can tell how it feels when constantly in hard! It's again healthy now...and lovely in soft mode.

I should maybe stress that I don't imply the car is too often in hard mode. What I worry about is that, when (correctly) in hard, its spring/damp relation is not good at all (almost non existing damping). It feels like the gas only is left witht the task of fading the pumpy motion. Noz, if you look at the Hydractive II tables, at e.g. 70mph, 20 or so degress of turning the steering wheel is enough to make it swithch suspension to hard mode. 20 degress is how much you would typically turn it on a common long-ish motorway curve at 70ish. The car then correctly stays in hard till you are back to straight line as the 20 degree threshold is broken all the time in such a situation. Driving somewhat fast in rural roads, this becomes even more stressed and sometimes the car would appear ready to leave the ground, so much the front pumps up and down. I'm definite that, in the conditions I am experiencing, it would be better and safer being in the soft mode, even with the minus of the excessive roll. Note that I have driven the car with completely flat spheres from Germany to Scotland (when I bought it) and it was much better (compared with the hard mode), as it was like a sports car -as u say-. Hard and steady. No uncontrolable wallowing. I've had sporty cars in the past and I don't mind the hardness, but this is not what I am speaking about.

I doubt Citroen would have produced a car with such characteristics, that's why I believe something may be wrong with mine. Reason I suspect spheres orifices is because when we replaced the whole set of old spheres with other regassed ones, me and indy found out that the orifices were slightly varying. Obviously they took spheres/orifices from various cars and tried to mathch my spec to the closest. I don't know if they matched my specs, what I can say is they were slightly diferent between them (i.e. right to left). But the symptom alone, is simply absolutely similar to what you would get in any everyday car and changed to harder springs without adding harder dampers (I ve gone through that with other cars I had).

The first thing one can think is that my car needs smallest orifices on the corner spheres, so it will be in good control whin in hard mode. But then I am aware of the redesign Citroen did from Hydra I to Hydra II in order to correct Hydra I too hard feeling, by exactly transfering some degree of the damping from the corner to the middle sphere orifices. If I went for smaller orifices in my corner spheres, the softness of the suspension in soft mode would go for good.

I don't really know what to think, at the end it might be an inherent design limitation. That's why I asked other peoples' feeling on that, it is something that can be felt by anyone -unless you are an extremely slow driver-.

Obvious diagnosis is I have wrong orifices on the corner spheres but then this means with the right ones the car would loose in comfort...


PS unfortunately I don't have the means to measure spheres pressure and neither my indy does.

Hi George,

The 'probably enough pressure' needs to be checked to rule it out of any diagnosis. Clearly you could have a fully charged central sphere and flat wheel spheres. This would make it feel OK on soft but miserable in hard. I have a tester which you could use but you'd need to take the spheres off the car to test them. A photo of my tester is here:

Another likely possibility is that the orifices are blocked on the wheel spheres but not the central one. This would give the same symptoms.

The 'range of orifices' has me worried though. It means that the spec of each sphere has been mixed up a bit by previous owners/garages and is suspect. Please find attached the page out of the manual with the Sphere size, Sphere Pressure and Orifice Diameter all listed for the Hydractive models. I cant remember which model (Petrol/Diesel Turbo/Non-Turbo)you have (could you add it to your signature for future reference - 'my controls' at the top right of this screen and 'edit my profile' at the bottom left hand corner of the next screen). The 2.5TD is not mentioned in the list so I don't have a note of those. Is it possible to check all three parameters of each sphere against the list?

You can see the orifice size stamped on the orifice if you look at the bottom of a sphere or in through the pipe connection holes on the electrovalve block.

From your description I would suggest that you do indeed have a fault that needs correcting. I accept that 'softness' and 'hardness' are very subjective assessments but from your description I would agree that its too hard.

A bit more investigative work and we'll have it flying like the magic carpet ought to.


noz cool.gif
I found a paper where I had noted what we found on the day of change, a year ago, with indy. The spheres I had bought online from a firm called Autospares, - £21 each+vat, supposedly new but they were regassed ones- were:

[size/pressure/orifice mm]

400/55/44 400/30/45

400/55/44 400/55/47

So a complete mix up, at least in the orifices, as pressure I indicate was just the one originally printed on spheres -I didn't measure it-. All orifices are smaller than they should.

I remember I felt a complete sucker because of the quality of the product I got -specially as I had chosen them because they listed with every detail the differences in the spheres for each year's version on their webshop-, but then I was so happy because the car was transformed -all flat spheres when I bought it-...

Anyway, I think I ll change the front or maybe all corner spheres with completely new ones to start with...I ll report.

Hi George,

Just another couple of thoughts/observations to paint the whole picture.

The mechanism in the base of the sphere is akin to the operation of a standard 'shock absorber' which you find in other, less fortunate, peoples cars. The resistance to movement of the shock absorber (must rate as one of the most inappropriately named devices ever, its actually a damper, the spring is the shock absorber) is not the same in both directions. In relative terms it is easy to compress the shock absorber shaft but the greatest resistance is felt when trying to extend it. This philosophy extends to Citroens spheres. When the fluid is being pushed into the sphere, ie when the wheel is on the way up and the strut is in compression, the fluid passes through several orifices, 7 I think, as it enters the sphere. The 7 orifices are arranged in a circle around the more obvious centre one. On the way out however a large spring washer acts as a non return valve preventing the passage of fluid back through the same holes. The only hole the fluid can pass through on the way out is the centre one. Thus the greater resistance is felt on the way out.

Since some of your observations are qualitative by definition then it seems to make sense that you find another XM owner and drive their car. That way a comparison can be made which allows something approaching a quantitative assessment and therefore a bit more useful in solving the problem.

You've certainly got a mix of spheres there. Its difficult to make any reasonable assessment when the spheres are known to be incorrect (and now fairly sure they are too small in the orifice department) and have an unknown quantity of gas in them. The gas quantity could have been checked but now we know they are the wrong spheres it seems a pointless exercise.

Definitely worth considering a new set of wheel spheres if you really want to solve the problem. The incentive is that you could end up with the flying carpet you so richly deserve.

Best of luck.


noz cool.gif
Hi George,

You appear to have a rear suspension sphere on the nearside front strut, and two front strut spheres on the rear suspension. God only knows what you've got at the central (hydractive 2) locations. I'm confused by your reported damper orifice sizes, you can't mean 44mm, 45mm and 47mm respectively - approximately 1.75 inches, did you mean 4.4mm, 4.5mm and 4.7mm - still pretty huge, or 0.44mm, 0.45mm and 0.47mm? In which case how did you measure a hole difference of 0.1mm (about 0.004 inch)?

As Noz says, if you are going to experience the true comfort of the XM you must change your spheres for the correct ones, I believe GSF do new ones for about £22 apiece.

I would suuggest you also check the condition of your LHM hydraulic fluid. I don't know if you are familiar with it but it should be an almost fluorescent yellowy green in colour. Any sign of discolouration and you should drain it, flush out with hydraflush (you have to do about 1500 miles with the hydraflush in) and refill with LHM.

Thank you Noz and Derek,

Derek you are right, the orifices (should) be 4.4 mm I guess and not 44 mm of course! These numbers were stamped on the valves. Also, I have completed the process of hydraflushing, cleaning filters etc and, trust me, if my LHM was water you could drink it without any fear!!

The funny thinkg is my current orifices are smaller than the required but this doesn't make sense as my problem is that the corner spheres (ie when car is in hard mode) seem not to be damped enough, so what would happen if I put the correct, larger orifirces?!?

An important question. Noz, are you positive that the sphere data -the orifices specially- in the sheet you pasted are valid for all XMs and not only e.g. for Hydractive I ??? It would seem rational to assume that Citroen played around with various minor changes in the specifications through time. The reason I had bought spheres from Autospares is that they listed 3 different mixes of sphere specification for my model (12v V6) depending on the date of production, and I was kind of satisfied with that -as opposed to other outlets that typically sell one mix of spheres for e.g. "XM V6". Autospares sent me rubbish of course but that's another story...

I have thought of putting an advert for anybody willing in Glasgow to test-drive my car and tell me if it's very different than theirs, I might eventually do it.

Anyway, new front spheres next week to start with. I ll report.

thanks alot
I finally went to my Indy today and fitted new AMTEX front spheres (corner+middle), to start with, in replacement of some regassed ones I bought 1.5 year and 6000miles ago.

The car is now formidable. After passing from some local "check" points, and some motorway miles, I felt pure admiration for all the people who contributed towards the realisation of the hydropneumatic suspension.

Diagnosis: one of the corner spheres was clearly shot. This was probably the reason why the front was like a kangoroo when in hard mode: the middle sphere being cut out, the front relied on one half-empty sphere for suspension! The other one being just full of LHM...

Also, amazing to me, is the feeling of the "hard" mode now, which is not hard at all really. You can feel it effectively controlling the car's body, but is not really "hard". My hard mode till this morning would make...your teeth fall off, and was very distinct from the soft mode. Taking into account my recent diode problems (fixed now), I suspect that the car was often/continuously in hard mode but I couldn't be sure at the begining of that as, when spheres are good, the soft/hard difference is not so distinct ( eg. it could be easily misinterpreted for half-empty spheres). The corner spheres were working alone all the time, producing a shot front sphere and pushing me to realising that something was going on with my diodes, and the rest is history...

Now I'm tempted to go for all new rear ones as well, but I can't imagine how better it can be...Althoug they have to be in pretty bad condition taken into account that the car was running with the rear continuously in hard for 3 motnhs at least before I realise it (because of the front diode starting going bust in January).

On the side of this, I'm about to measure the cut in/out pressure of my pressure regulator. Was thinking BTW to permanently install a gauge I bought in the engine area, connecting it after the pressure regulator outlet...

So, I have a goddess indeed Noz...

George (really happy)
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