Citroen XM written up at The Truth About Cars

[Peter.N.]

The ride is good - just not at low speed. I'm sure they could have come up with a solution, Rolls Royce use hydropnumatic and they seem to ride well at low speeds, just watch one when you are following it, could be because it weighs about 3 tons of course.

Peter

[casalingua]

I drive around in town a lot so that means a lot of low speed driving. In terms of time in the car I experience a lot of hours of crashy ride. In terms of miles covered I do far more inter-city driving than in-town driving. We don´t have Rolls Royces around here so they are hard to observe. Given my interest in ride quality I find the legendary Peugeot 604 an appealing prospect but also offerings by Cadillac (early 90s cars) have their attraction. The huge fuel consumption of Caddies is the main bugbear. I could live with the American-style opulence and rather hamfisted styling.

[Dieselman]

Different manufacturers spheres give different bump, shock absorption. I recently changed some unknown ones on my car due to them being crashy, even with full gas pressure.

[White Exec]

Peter's right, I'm sure . . . Body weight has a lot to do with the comfort available. Ideally, all the weight would be "sprung" - i.e. the wheels and associated clobber would perform the function of providing contact (grip) with the road, but weigh nothing at all, and the suspension - the bit with the "give" - would be totally absorbent. In the real world, keeping the unsprung weight (wheels +) as low as possible is the best one can hope for. Some manufacturers have opted for in-board discs for this reason.

Given that unsprung weight can only get "so low", then a really heavy vehicle body (a la Rolls Royce*) helps. It's purely a matter of inertia: on the move, a 2- or 3-ton body will be hard to accelerate in any direction, including vertically. That means that, given a road bump, the body will continue in its relatively undisturbed straight line, and the suspension (hydropneumatic, air [as it now is on R-R's] or whatever) will have to absorb the disturbance.

At the other end of the scale, a heavy under-carriage (modern wide and heavy wheels) coupled with a lightweight "fuel-saving" body, just presents a shed-load of problems for the suspension designer.

Perhaps the ideal suspension for a rippled and pock-marked road surface might be 'hovercraft', but then the cornering would leave something to be desired!

It does seem that hydropneumatic suspension has survived only on relatively heavy vehicles: the large Citroens, recent Rolls-Royce, Land Cruiser V8, and some military tanks. It's probable that it would never have worked on a Mini, irrespective of cost, although the BX (with its long wheelbase) showed just how far it could successfully be pushed.

* Clarkson's back-to-back 'test' on a RR and its sister Bentley contained one amusing line: Where the Bentley glided over the bumps, the Rolls (with its additional 400lb weight) actually flattened them.

[Dieselman]

To get a truly jar free ride, the spheres need to have supple damping and the connection to the body needs to have plenty of rubber in it. Mercedes cars generally do this well as they pay attention to that aspect, even if the car is stiffly sprung.

[Peter.N.]

I came back from 'up north' with two diesel engines and a gearbox in the back of my XM, no complaints about the ride then - performance wasn't very good though.

Peter

[jorgy]

casalingua,

I had the same issues you describe and couldn't accept it was designed to be like that -as bad-, after having fixed all hydraulics (spheres, pressure regulator, electronics) and the car still not being good -too crashy on pot-holes, not absorbing the smaller stuff too well.

2 of 3 XMs I have, had sticky front struts. This was cured after doing as-many-as-possible citrobics everyday, whenever I could, on Hydraflush. The giving sign is that they literally stick and noisily groan when, from highest position, you allow the car to fall. Also, on one of mine they were so sticky that the front would go up in steps (very noisily too near the top), instead of doing so in a continuous and silent sort of fashion. You could well hear the struts groaning from within the cars, doors and windows shut. What I describe is: go up 2 cm, stop for a moment; go up another 2cm, stop again; and so on. On one of them, the LHS was stickier than the right so that when allowing the car to fall from top, the RHS would move first and a fraction of a second later the LHS would follow -and this was with me seating at the LHS too! If your front struts are not sticky, the front should be going from lowest to highest in a pretty much linear, uninterrupted manner, and without any noise whatsoever from the struts (obviously it slows pace near the very top end as the system has to compress the spheres.)

After lots of up-downs, the noises and spasmodic movement is gradually gone/minimised. This is a broadly recognised problems with BX front struts, but not with XMs. I suspect it doesn't depend on age only, but mostly on the life the car has had. I once bought a set of used struts from a 1994 XM that had been last used in a banger charity race. One strut was sliding fine, the other had so much play as to be well sensed by the hand, and the ram had signs of blue-ish hues (heat)!! I assume this is what happens when one side is driven on a flat sphere for too long a time. Not to talk of people driving on LHM that looks like mud, or even on other non-LHM oils.

Re. the rear, the cylinders are much more solid than the front design, but have you considered whether the bearings are okay?
Also, what about the subframe's 4 bushes -they can't be that good on a 1990 car.
And you shouldn't exclude the most extreme things imaginable, e.g. I've seen broken ram pushrods in cases of cars driven on flat spheres again.

[casalingua]

This is what Car magazine said in January 1990, when comparing the XM to the BMW 520 and Lancia Thema 2.0 :" It's jittery around town and will slap its tyres over ridges". Nearly all the reviews say something critical of the car´s low speed ride and capacity to deal with surface bumps and cracks. Did you manage to improve the ride on your car sufficiently to disprove these failings? I have noted your diagnosis list and will consult my mechanic. I regret not attending to the rear bushings when getting the rear sub-frame welded in Holland in June. I suppose it´s a horrible job to do. My Danish mechanic didn´t like the idea of dismounting the sub-frame which is partly why he refused to do the welding. I may have to leave this until another visit to Holland. I´ll look into the front suspension first.

[jorgy]

My conclusion is that the only issue really inherent in the design is the bad reaction on *very* sharp bumps/holes, i.e. broken tarmac as from freezing. In this instance, the front struts thud not nicely, and it's felt through the body of the car. But I wouldn't describe it at all as "jittery around town" -very unfair a summary of its ride.

The one thing I've noticed that is echoed in the various tests is, often, in slow cornering, you feel you are faaaaaalling Paradoxically, in faster driving and cornering you won't feel that, as it will have already switched to "hard". You don't feel it either in "sport" mode. "Sport" mode on a HII is actually perfect for my liking.

I don't know either about what's described as "tramlining" in the various tests... maybe it is that I never cross any tram lines!

In general, overall, you should be very happy with a normally working XM suspension, and things said around the net -even in french fora!- e.g. that "hydractive cars are less comfortable than non-hydractive" (Xantias, XMs) is just urban myths, hydractives are *more* comfortable than simple hydropneumatics and that was one of the points of making it. The "not so comfortable" cars are, 99%, simply cars with problems. 1%, people that had been used to DSs and CXs and will just find anything not as low-frequency (talking of suspension frequency) "not too comfortable". If you are not-so-happy and it's bothering you, 99% it means something is not right.

Listen, one test I did after having fixed a number of things and still thinking that "this isn't so comfortable as to justify the Citroen myth", is to drive around with a simple voltmeter connected to an hydractive valve (just pinch with a needle from the ECU, pins 1 and 2 for HII). This way I could say at which moments the car was "not-comfortable" because it had switched to hard mode, and when it was "not comfortable" even though it was in soft mode. This way you will also check that the electronics are not switching to "hard" too soon (= too often), which is one thing that can happen. My TD car is switching way too easily to "hard", and this is on my "to do" list... By all means, even better, have your hydractive ecu read by a diagnostic machine (elit, lexia), what you might find is priceless compared to the cost a dealer will charge to do it.

Rear subframe bushes are not a difficult job actually. Never done mine, it's on my "to do" list for one of my cars. From what I've seen from others, you just need to drop the subframe as much as to take them off and then insert the new ones -no need to undo anything else. So it's a job doable independently of any other work. Problem with these bushes may be availability -I had read somewhere here that Cit UK (I realise you're not in the UK) doesn't hold them anymore and that one could buy Peugeot 605 ones wichi are identical -but are they?

And don't forget the rear axle bearings -any XM with the mileage and age they're now at, could prob do with a new set. You don't need to wait till the rear wheels develop camber. I bet the rear axle ride of an XM would be transformed with new bushes and new bearings. I've done nothing of these on any of mine though, and they were all nice and soft enough once the rest was sorted.

Never seen anybody putting new front struts either -neither have I, although I have a brand new pair. You can't assume they're ok if at least you've not removed them and see how they slide -and even this will only show large damage -as per my example. I wish I knew how this damaged strut would behave on a car, it would say much on what degree of wear gives what results.

[jorgy]

Forgot to say -and sorry if you already knew this- that a basic test to see whether your car is switching to soft mode at all, is to remove the hydractive ecu fuse -under the dash fusebox. Engine running, stationary, fuse off, you should get a rock-solid suspension. Fuse back in, and you should be able to push the car down quite a few cms. If there's not difference at all, then your car doesn't put the middle spheres into play at all. Could be due to any, or both, electronics and hydraulics.