Odd suspension issue ?

[HDI]

In the past I've complained about harsh suspension on my X2 HDi, even after a complete change of all spheres and LHM etc. It works fine over large amplitude bumps etc but on sharp edged ridges etc it's quite harsh. The other day though, I had raised the suspension to full height to access the underside, then lowered it, but with the engine not running. Afterwards the suspension was noticably softer and much better behaved over sharp bumps. Gradually though it goes back to being harsh again but I can temporarily soften it with the raise to full height then lower with the engine off trick. Does this point to any particular fault ?

[citronut]

sticking/seized height corrector turrets/linkage's,

the only way to free them off long term is remove them from the car,
then lub and work then lub and work then lub and work then lub and work then lub and work till the turrets are floppy loose,

now smother them on grease after refitting them

[HDI]

Not convinced that will be it, I've kept the height correctors sprayed with grease ever since I've had the car and it never has a problem with ride height.

[Mandrake]

Same problem here HDI, with both my current V6 and my previous 2.0i - both hydractive 2.

Ride quality over small sharp bumps can sometimes be surprisingly harsh, perform one round of Citreorobics and the ride is often (but not always) a lot better for a short period of time (almost magic carpet) that can be anywhere from 15 minutes to a couple of hours, then it reverts to being more harsh again.

If it's left to sit on high for some time before lowing the improvement is more pronounced than just raising it then immediately lowering it.

Despite doing a LOT of work on the suspension on my previous Xantia I was not able to resolve the issue nor conclusively identify the cause or causes, and I believe that to a greater or lesser degree it is a common problem with Xantia's past a certain age. (eg all of them, by 2012 )

Current pet theories of mine on the cause of the problem(s) in descending order of likelihood:

1) Air leaks in the low pressure return lines back to the hydraulic tank causing air to be drawn in causing excessive aeration of the oil in the tank, exceeding the ability of the filter to burst and disperse the air bubbles, leading to air bubbles being sucked into the pump and pumped into the suspension.

On my previous Xantia I had a clear section of hose from the tank to the pump for a long time and conclusively proved that very visible and obvious amounts of air bubbles were being drawn into the pump, particularly when the car was hot (why when hot ? I don't know)

Air bubbles in the suspension are known to cause harsh ride due to hydraulic hammering of the pockets of air - the whole point of Citreorobics is to expel such air bubbles, however if air bubbles are being pumped into the suspension at an excessive rate the cure is only temporary.

Anti-sink makes the problem more of an issue because the car is not self purging each night, any air bubbles in the suspension will tend to stay there and accumulate unless full Citreorobics are done. Hydractive 2 also makes the problem worse than standard hydropneumatic as its much harder to purge air bubbles that accumulate near the strut top due to the long length of large diameter pipe from the strut tops to the hydractive regulator.

To expel the bubbles they must flow all the way down to the hydractive regulator and then back to the height corrector - if they don't reach the height corrector they will just find their way back to the strut tops again after a short time, so small height corrections of people getting in and out is not enough, it has to be a full Citreorobics up/down.

I believe air bubbles being pumped into the suspension is a major issue of intermittent harsh ride quality, especially on hydractive 2.

2) Partial hydractive failure, causing the shuttle valve in the hydractive regulator to move back and forth in response to bumps - in other words you hit a bump and the act of hitting the bump causes the valve to momentarily switch to hard mode, thus causing a jolt.

Two theories on this - one is intermittently or permanently low main system pressure from the pressure regulator. This has been empirically proven as a fault by a few people on different forums, basically the main system pressure has to be a lot higher than the suspension pressure for the shuttle valve to be "locked" in soft mode, if the pressure is too low the pressure jolt from hitting a bump will cause the valve to momentarily slide to the hard mode even though the electrovalve is still on, causing a harsh jolt. The solution to this problem is to test the system pressure and if necessary recondition or reshim the pressure regulator. As far as I know my previous Xantia didn't have any problems with low system pressure.

The second theory is a leaky electrovalve. If the electrovalve has sufficient overflow leakage it may not be able to "lock" the shuttle valve firmly in soft mode and the end result is much the same as low system pressure - sudden pressure spikes from bumps may be able to slide the valve to hard mode causing a jolt. My previous Xantia did have a seriously leaky front electrovalve and replacing that did give a noticeable improvement although I wouldnt say it was a complete cure by any means.

3) Strut shaft wear at the normal ride height position - on my previous Xantia the smooth hard surface of the strut shaft at the point where it rests against the top bronze bushes was badly worn and rough/textured in appearance. (pictures in one of my threads on the forum..) setting the right height slightly below or above normal made the ride noticably less harsh. Full Citreorobics helps to lubricate the shaft very slightly but it's only a temporary improvement, likewise greasing the strut made quite a big difference but would only last a few days at most.

Then of course there are the normal well known issues like electrovalves with faulty diodes, sticky height correctors that aren't regulating the height accurately etc, but I don't think that's what you're noticing.

I still believe that issue number 1 is the major factor, and it could be as simple as ageing rubber return hoses developing small air leaks at junctions - not enough of a leak for low pressure oil to leak out on the ground, but enough for the flow of oil to draw in significant amounts of air.

Identifying which pipes seems extremely difficult though, in my experience the air bubbles will continue to arrive in the tank even with the car stationary, which means it must be the return from the power steering and/or the return from the pressure regulator that are allowing air to be drawn in...(possibly with other sources of leakage as well, such as suspension returns)

Anyone else have any thoughts and ideas on these issues ? I would really love to nail this problem once and for all, especially after trying and failing for 4 years.

[Mandrake]

Just dug up a few pictures from my previous Xantia taken when trying to track down the intermittent harsh ride issue. (I've posted about it on the forum a few years ago too)

The first is the worn strut shaft, not sure how well it will be visible in a scaled down image, but here it is:

The next is a picture of my clear piece of hose. I just remembered that I had it attached to the main overflow return line, not the line to the pump (although I did try that too) this is the return line that goes to the "octopus" junction that I think includes the pressure regulator and steering return lines along with all the other "high volume" return paths, like height corrector returns:

Obvious intermittent bubbles of air would flow back through this pipe - sometimes enough to cause serious frothing in the tank.

Finally this picture is a picture of a potential source of air leak on the line to the pump - there is a small plug with an o-ring on it as indicated, I'm not sure what its purpose is, but if the o-ring was worn out and leaking it would in theory cause the pump to draw in air:

I don't think it was faulty on my Xantia (didn't make any difference replacing the o-ring) but its something thats easy to check.

[HDI]

Interesting. My theory is something to do with the Hydractive ECU, or a reset procedure that may be required after any work on the system.

[Northern_Mike]

Interesting. My theory is something to do with the Hydractive ECU, or a reset procedure that may be required after any work on the system.

My theory is that that all Xantias have this issue, even my old M-plate 1.9TD had it, with all new spheres and fresh fluid. The Activas, RUNN and Rattiva all have it too.

I think the XM did to a small extent. That had a weird problem where it would "dance" in small oscillations, but only when parked at the traffic lights on Putney bridge coming out of London. I never did work that out.

[Mandrake]

Interesting. My theory is something to do with the Hydractive ECU, or a reset procedure that may be required after any work on the system.

Whilst the ECU can certainly have problems - mainly in the form of faulty sensor data, I don't think this explains what you describe at the start of the thread.

At worst all a faulty ECU or sensor data can do is cause the electrovalves to be commanded into hard mode permanently or more often than they should be. (Remember the ECU is constantly switching between soft and hard during driving depending on conditions, every time you accelerate from a stand still you're in hard mode for about 3 seconds for example)

With my previous Xantia I found that the harshness was actually worst in the "soft" mode, if I forced the suspension into hard mode by removing the ECU fuse the ride would be firm and heavily damped but not harsh in the same way. This lends some credence to pet theory 2 (above) that low system pressure or a faulty electrovalve is allowing the the shuttle valve to be dislodged from the soft mode momentarily by the pressure surge from hitting the bump - because when the suspension is already in hard mode an additional pressure surge will only hold it more firmly in hard mode, not causing any issue.

As far as I know, there is no "reset procedure" in a Hydractive ECU, the recorded fault counters can be cleared with a Lexia, but this has no bearing on the functional operation of the ECU - it performs ongoing diagnostics both while driving and during power on that will cause it to recover from temporarily faulty sensors or electrovalves etc...

[Mandrake]

Interesting. My theory is something to do with the Hydractive ECU, or a reset procedure that may be required after any work on the system.

My theory is that that all Xantias have this issue, even my old M-plate 1.9TD had it, with all new spheres and fresh fluid. The Activas, RUNN and Rattiva all have it too.

After the amount of effort I put into trying to solve this issue I started to come to the conclusion that it may in fact be a design flaw or the cumulative effects of multiple design flaws. That's not to say that all Xantia's necessarily exhibit intermittently harsh ride (obviously not) but that there is a tendency towards it especially as they age, and past a certain age it may start to become inevitable. (unless we can figure out the cause)

One reason I hunted for the explanation so obsessively is that older Citroen's do not seem to suffer from this issue. I spent many years owning, driving and working on both the GS/GSA and CX, and from everything that I can recall they did not suffer from this issue of much smoother ride for a short period of time after Citroerobics followed by ride harshness, nor did they suffer from intermittently varying ride quality that can vary so much from day to day. It's something inherent to the design of the Xantia that causes it. (I can't speak for the BX as I've never driven one)

If you compare a GS or CX to a Xantia there are a few major differences:

1) No anti-sink system in the GS/CX. This means any air bubbles that might accumulate in the suspension would self purge each night, therefore no ongoing buildup of air bubbles.

2) Hydractive 2 introduces very long very large diameter piping from the suspension struts to the height corrector, making it that much harder to keep the suspension purged of air bubbles.

3) Transverse parallel arms in the GS/CX versus McPherson struts in the Xantia - the transverse arm pivots have very low static friction even when loaded with cornering/accelerating/braking loads, while the McPherson strut has higher static friction that increases dramatically with directional loading including cornering. (Eg harsher ride on smaller bumps) The McPherson struts also have a tendency to wear at the normal ride height while the rotating bearing of a GS/CX top arm can wear but don't really wear in one particular spot. (The needle rollers are free to redistribute themselves around the bearing cones)

4) No power steering in the GS, and in the CX the power steering (Diravi) is of the type that no oil flows through the steering when the steering angle is stationary, with only a brief flow of oil as you are actually moving the steering wheel. By contrast the power steering in the Xantia is constantly passing through oil back to the tank when the wheel is stationary and reduces its flow when the steering is under load.

This means that there is a constant very large volume of recirculating oil flow through the steering and back to the tank in a Xantia which is not there in a GS/CX which helps to froth up the oil in the tank and provide a potential source of sucking in air bubbles if there are any air leaks in the return piping. (In my testing it did seem that the power steering was the largest source of air bubbles returning to the hydraulic tank when the car was idling stationary)

I think all of these factors combine to create a perfect storm which results in intermittent ride harshness that gets a lot better after Citroerobics but then gets worse again fairly quickly. Whether its something that can be "fixed", or at least cured by some sort of modification(s) I'm still not sure.

My V6 doesn't seem to exhibit the problem nearly as much as my previous Xantia but the same tendencies are definitely there, with a ride that is occasionally rather harsh, yet often quite decent the very next day...

[HDI]

I think the most significant difference between the GS and CX is that they are mechanical systems compared to the electronically controlled Hydractive system. I am less convinced by air in the fluid because as the fluid is returned to the reservoir it becomes de-aireated, like a dry sump oil system. Also, most of the return fluid is from power steering anyway, as far as I understand it anyway.

[red_dwarfers]

A very interesting topic, though it's not something I've really taken much notice of.

To rule the PAS in or out, if time was not an issue, could the PAS be run off a separate LHM supply? Maybe a second hydraulic pump could be fitted in place of the air con one? It would certainly be an interesting project!

[Gibbo2286]

Just a thought about air bubbles in the system, wouldn't that have the opposite effect i.e. soften the ride, air being compressible?

I found on the last Xantia I owned that if you hit a speed bump with both front wheels it tended to shock the system as though there was no give at all.

[Northern_Mike]

Just a thought about air bubbles in the system, wouldn't that have the opposite effect i.e. soften the ride, air being compressible?

I found on the last Xantia I owned that if you hit a speed bump with both front wheels it tended to shock the system as though there was no give at all.

Yes, all mine have done this. There's a particular ridge on the A4 near Burchett's Green that sends a big shock right through the car. It's right where one needs to brake just before a mini roundabout too, so feels particularly nasty as the front end is loaded up at the same time. I've taken to slowing down before I get to it, though that can annoy people behind..

You can see the ridge here (google streetview link) http://tinyurl.com/nastybump" onclick="window.open(this.href);return false; - right across the road, it shows up well because of the damp!

[Xantianut]

Ay up!

I've had BXs then a Xantia for about 20 years now and only had this problem with my last BX and a BX diesel when the struts were partially seized. With the Xantia, I've found that a smear of LHM on the strut then Citerobics (I like that!) has cured the problem. Needs re-doing every 6 months or so, keeps the seals lubricated, then of course wipe clean the strut to stop it collecting muck.

I reckon that height corrector probs can be ruled out. I had one go wonky on a BX which was either full height or on the bump stops at the back. A corrector, certainly on "traditional" systems, just stops adjusting rather than gives a harsh ride.

[Spaces]

I like your clear pump supply pipe, Mandrake. If a few people fitted these and observed fewer/no air bubbles after an overnight stop or Citroebics which corresponded with a smoother ride then the case can be proven to be at least part of the problem. If it is, has the change in design of the reservoir interiors promoted air into the pump? Unlikely I know but perhaps worth a look.

If air does enter the HP side then I'd have thought there was the potential to play havoc with pressure further round the system . Could this be affecting operation of the electrovalves? I'm lucky enough to have never experienced this on any Xantias, other than the harshness induced by the compromise of grafting the hydraulics around a layout intended for metal springs.

From what I have seen, Citroen had almost as little appreciation of its own suspension as does the public at large, by the time the Xantia was being built. What makes me say this? - no reference to how to change a wheel using the suspension's movement in the handbook, steady alteration of the sphere design which has led to increasingly jarring low speed ride/poor ability to absorb smaller amplitude bumps and ripples and then the decision to abandon the time-proven design and use seperate electric motors for each corner on the C5 (at a stroke deleting the wonderful interconnection of rear brakes and suspension) on the advice of a bureaucrat in Brussels in the interests of safety. So, unwittingly building in a design fault would hardly be surprising.

The good bit is that people on here are aware of this recurrent problem and if it is air, should be fairly easy to eradicate.

As an afterthought, would those running comfort spheres experience just as much harshness?