My XM's rear ride was getting bumpy and it was taking a while to gain height in the morning, so I surmised that the rear spheres were flattish. As I run CX rears on the rear of the XM to help counteract some of our appalling road surfaces here, this loss of pressure was becoming annoying.

Anyway, I finally got to on the weekend, hauled out my motorised sphere tester (another story another time) and started testing my stock of spare spheres. I have had a deluge of parts land on the door step recently, especially since we took possession of the CX.

Anyway, I eventually found two that had more than enough gas, and sorted the savable from the chuckable. The decent pair turned out to be BX fronts, that are normally gassed to 55 bar, yet these were at 65 bar! Someone got carried away when they regassed them.

Well knowing that I was only going to and from work, and that I would have a chance to get the others regassed by a fellow club member, I put the 65bar pair on. I knew it would be soft, but hmmmmm......

We have a D Special, which for those in the know, has the older style adjustable plate spheres on the rear. It is a very soft town car, yet is fine on the highway. For those who are used to a D's slight pitching from time to time, the XM was certainly an experience.

With the shorter relative wheelbase of the XM and that the wheels are less "at each corner" than a D, the pitching wallow was somewhat off putting. I ended up driving the car mostly in sport setting so that any corner encountered would be more likely to give a firmer suspension reaction.

Tomorrow morning the regassed rears go back on the car. I think I will cease singing sea shanties as I drive the car from that point.

It was a good way to make do, but not something I recommend for regular driving. I am looking forward to the return of normality to my XM.

By the way the CX rears at 40bar work quite nicely on the back of the XM.

Very interesting...So u used something with, like, a 1.6mm orifice at 65 bars ?? And what's the orifice on the CX ones you normally use?

I'm not satisfied with my XM: although it's wallowing and is soft in general, it does not behave well in more abrupt surfaces. Part of it must be because it's an XM, not a DS or CX, it's firmer in damping. But, especially interesting are some moments where the suspension reacts like it had momentarily "frozen". Is this typical of the hydropneumatic suspension? I remember reading in various old road-test things like "...ride is very soft but it has the typical judder of the hydro-suspension in things like rail-tracks etc". Is this what I'm discovering? I was wondering, is this some unavoidable quality of the LHM+gas as a medium for spring? I was thinking if perhaps I have sticky struts, i.e. they are not free to move quick enough in those more abrupt...encounters. The behavior I get is similar to such an effect. Also, even at motorway speeds, if there is a (rare) pothole-depth kind of hole, the car tends to "fall" in it, rather than the wheel fully absorbing it and the car remaining relatively undisturbed. I.e. it acts like a firmly-damped car. It reminds me of a VW Polo which I drove recently and I thought "that's a hole-hunter", you had the impression it was "plunging" into every hole on the road. So there seems to be a problem not only in compression but also in extension of the strut. Or is this just how the XM is set to be? I didn't expect this behavior even at motorway speeds. What are the symptoms of sticky struts? I read about the car rising "in pieces" rather than in a linear manner?? Another observation I have for the XM, after 3 years of ownership: how strange is that when the car meets an object with both wheels, it absorbs it fully, but when same object is met by one side only, it cannot absorb it well . This performance is valid under any condition, ie flat spheres, stuck in hard, wrong height, unproper pressure from p.regulator, always the same (proportionally of course). I cannot explain that. No matter how much I look at the hydractive design schemas.


regards
George

ps. everything else relevant on car works as it should. New evalve in front whose high-pressure feed I have even isolated with a 1-way valve to make sure it is there, pressing it open at all times. Spheres at 90% of nominal pressure, electronics Ok, height correct, pressure regulator checked and tuned.

The single-sided response seems to be the norm. I have a sports centre with rather sharp speed humps,; if you are wise to aim to hit them straight-on or suffer for it. Similarlly, when crossing a rutted track in a field, it is not safe to be going at more than walking speed unless you wish to have your head banged on the door-window due to the excessive roll. The XM suispension does not control the anti-roll bar ends separately.

So you put it down to very thick antiroll bars then? This makes sense with regards to the single-side behaviour. Is there a tight limitation then in the hydropneumatic suspension with regards to the trade-off between comfort and body roll? I thought in the XM they had resolved the roll issue with these little balls included in the hydrative blocks, that stop the crossflow of LHM between sides.

Still, there's an obscure area about the "crashing". Any conventional car I've been in, soft or firm, doesn't "crash". My XM can be "crashy" even in instances when both wheels meet the same object (not speed-humps, it's good with those). Rather in sharp formations, kind of crossing a train rail, or tarmac holes where the edge is "cut", no matter how deep the hole is. Could it be a matter of the natural frequency of the hydropneumatique suspension -perhaps there's a small frequency range where it performs bad?-.

Also, my XM allows all sorts of tiny road unevennesses in the cars body, again the feeling is that the suspension does not give in to absorb these. I suspect this is why traditionally they say that Citroens ride better on Michelins, ie soft tyres -I take it they were soft at some point of time, don't know now-?

Do others notice the same or is my car not really well?

G

I was watching an XM commercial on Youtube the other day, it had footage of the car totally level and the front wheel bumping up and down like it should do with a computer adjusting the stiffnes at 30Hz.

It took many years to get my old one riding decently, all new spheres and an electrovalve and a flush did it in the end, but I'm not convinced its that good still. It did used to "crash" at the rear (I assume we are talking about the same thing) but hasn;t since all that work was done. Plenty of other problems though.

My new one, well its doing my back in, seems to oscillate 2.5-3.5 times at about .3 Hz
when hitting anything slightly resembling a bump, booked it in at the indies today just hoping it won;t need all 8 doing at once.

Tried to find the youtube vid I mentioned it but it seems to have gone, but this one has similar footage about 25% in and is quite good, would be even better if my German was any good.

http://www.youtube.com/watch?v=FL00DqL1ePw...related&search=

Presumably the engineers who designed it had computer simulations of the hydraulics?
As it seems quite difficult to diagnose a model might be useful. Anyone got anything like that?

make that 3 Hz not .3 Hz.

sounds like flat spheres or suspension stuck in hard.

G

I have had similar experiences with the XM ride. I have driven others which seem to ride much better than mine over small sharp bumps. Now I have two and can compare them, I have come up with an answer - tyre pressures! The recommended pressures for the estate are 33 psi all round, reduce them to 30, assuming that you are not carrying a lot of weight, and the ride improves tremendously, lower is better still - not of course that I am recommending this course of action.

Peter.N.

Hi Peter,
so you say XMs are not like that normally. I logically tend to think so, there couldn't be all that fuss about the hydropneumatic suspension if it behaved *that* bad in those specific situations. However, with all this contradicting information -e.g. CX-fans repeating "the XM's no good", motor-journalists often having written things in the style of "the Citroen suspension has been now largely surpassed from conventional designs (for comfort)", it makes you rationally examine the possibility that, perhaps, the image of amazing comfort was true in the 70s and 80s, compared to other contemporary cars -specially with the soft set-up of those Citroens- but should not impress us today? Still, I rationally conclude that no car maker would have put on sale a car that's so dissapointing like mine in the specific situations described above, and, at the same time, claim it's very comfortable. So I keep on faring with the assumption something is faulty.

Will other people please also share their experience here? How do your observations compare to ours? How does your XM ride?

George

Hi George

Not having driven your car, I obviously cant say that yours is any better or worse than any other, but having owned and driven CXs for many years and miles, I was also of the opinion that the ride was much better - until a couple of months ago, when I drove one again. It was a 25 DTR Turbo estate which I was considering buying, but do you know, I was quite pleased to get back into my XM again! Admittly the spheres on the CX were not brilliant, but the general comfort and noise level of the XM was better.

If you are sure that your electro valves are working and that all the spheres are good, especially the centre ones, unless you have some mechanical problem, which is unlikely, its all down to the tyres, not just pressures but carcass flexibility and ammount of tread.

Having said all this, I find that the ride quality is very much subjective, if I am relaxed and feeling well, the ride is usually superb, if not its dreadful!

There is no doubt that cars of yesteryear did have a better ride, but I am sure that was basically down to cross ply tyres. I do remember the ride from my Morris Oxford estate, you couldn't feel a bump. I also remember fitting radials to my Morris Minor van for the first time, ugh!

I can only suggest that, if you have not done so already, drive someone elses car, several if possible and compare, but check the trye pressures first. If your anywhere near Lyme Regis, you can try mine.

Peter.N.

Hi all, just to add to DRTIM'S input, the flush through IS a very important part of XM suspension maintenance and in my view should be performed at no more than two year intervals - regardless of mileage but certainly less than 30000 miles. Having been in current models of merc,bmw 5 and omega's,nothing matches the subtleness of ride of my 2000 XM. I notice that the flow distributor and pressure regulator haven't been mentioned,my advice is get them away to PLEIDAES for overhaul, the cut in interval for the PR with a good accumulator shoul be no less than 30 seconds tested with the suspension in NORMAL and engine idling. Remember ,these two devices govern the operation of ALL the hydraulics (steering , brakes , suspension) and are paramount in sytem performance.Make sure these components are doing their bit FIRST.

Yesterday afternoon I refitted the regassed spheres. Today we went to Sydney and back and it performed beautifully. Life is better now.

Hi all,

well, Peter, it seems my XM is not performing as it should, Robert's input proves this. I've riden many times in a friend's BMW E39 2lt (the model just before the current one) and appreciated the way smaller holes etc were not transmitted through to the car's body -I expected they would be to the sporty side, but BMW's are clearly far from VWs and Audis these days, for comfort-. Of course, as speed rises, it behaves more and more like a typical spring-suspended car.

Robert, your testimony is very worthy because your car is newish. Note that my car has no FDV (it's a 3lt Diravi lhd) and the pressure regulator has been checked ok. My middle front sphere is about 60 bars, instead of 70-75 normally, but I don't thing this will make the difference. My front corners are also about 10% lower than the nominal.

Afaik, the centre orifice in a sphere makes for the "wallowing" effect on a Citroen, while the metallic disks on each sphere open up to uncover the bypasses that let LHM pass in higher frequency motion of the wheel, e.g. bumps etc. My car wallows well, but it performs like those disks were not opening properly, or, like the wheel for some reason could not move fast enough to follow the bump/hole. The later would suggest sticky struts. The former though makes me think: perhaps my front struts are leaking sooo much that, when the wheel hits a bump, some LHM also escapes through leaking back, instead of all being directed to the 3 spheres available to absorb the motion. Thus, perhaps, at those violent cases (sharper bumps/holes) the disks on the corner spheres don't quite have the chance to open up as designed to, and mostly the middle sphere is left to do the job -and it does it, but not well enough-. This would explain the "crashy" feeling.

Another possible cause on an older vehicle would be the rubber parts of hte suspension, ie wishbone silentblocks and strut tops. My wishbone rubbers passed the MOT last august with no comments so they must be not bad. I wonder though as to the effect of fatigue of the rubber at the strut top with years -presumably it has some role in smoothing out the smaller road unevenessess-.

Another senario I'm thinking of lately is that the very hydractive valve perhaps suffers from wear just like a brake valve or a strut piston, and leaks back. This would mean that, at a fast pressure increase (eg sharp bump), the suspension side can force the valve closed, while LHM passing fron the high pressure side into the suspension side. This would cancel the effect of a perfectly working e-valve.

The reason I'm into thinking all these, is that 2 weeks ago I put a new electrovalve in front. I also put a one-way valve at the high pressure pipe that feeds it. So that part of the operation can't possibly fail. The front e-valve on my car has constantly *at least* as much pressure as the max available at any moment. My regulator is tunned to 153-170 bars and not leaking. Electronics & electrics are working. Spheres as above. I don't believe my struts are sticky because I've had the car perform beautifully on one ocassion for 1 single day, last year. So, IT HAS to be something else that makes my XM not performing like Roberts!

I think one day I'll take my car to the garage and tell him to check the various return pipes one by one, for leaks. I think what I'll do is I'll choose an axis -front or rear- and replace all critical parts with new ones, slowly-slowly. I know it sounds crazy -and I'm not rich at all-, but if not, I'd prefer to sell it. I've already invested too much on the car to have it performing anything else than like a Citroen -that's the reason I bought it after all !-.

I never planned to spend so much on it though. Clearly the lesson here is "check in depth" when buying an older hydraulic car -unless you have £2,000 to treat it to new struts, valves etc.-

George.

regards
George

This probably isn't the whole story but I reckon that low profile tyres aren't helping. I think that being as it's the first point of contact with the bump they must have a reasonable amount of influence.

Steve.

Hi Steve,

my XM was specified for 205/60/15. That's not too low a profile but not thick either. But you are right I think, taking into account that older Citroens specifically rode on profiles like 70%.

With this respect, another detail just caught my eye somewhere else in the forum: somebody implied 2.5tds ride on 205/65/15 from factory. Was this perhaps a tactic reaction from Citroen to improve comfort? They certainly played with 2-3 different sphere specs through the years.

Robert, what tyres your 2000 XM uses?

regards
George