Very Strange Xantia V6 Suspension Problem

CypherPunk · Post by **CypherPunk** » 07 Apr 2007, 16:09

I’m experiencing a strange problem with my Xantia V6; I’ve changed the accumulator, anti-sink and the three rear spheres this morning and everything seemed to be working fine.

I decided to give the car a quick wash and then take it for a quick drive to feel the difference, so I tried a little citaerobics, set the car to normal height as was about to set off when the front of the car suddenly dropped down. Puzzled, I got out of the car and watched the front slowly pump up again, stay at the correct height and then drop down again after about 30 seconds.

Now it seems like the car is stuck in a loop, the front raises up, stays at the correct height for 30 seconds and then drops down for 30 seconds, this only happens with the suspension set to normal.

I’ve checked under the car for any leaks and I’ve definitely closed the pressure release screw so I’m not sure what the problem could be, is anyone able to shed some light on the problem?

AndersDK · Post by **AndersDK** » 07 Apr 2007, 17:05

I believe you have a sticky front HC linkage. This can give the effect of too high 'hysteresis', setting off the oscillating behaviour.
Have the car over a pit - or the frontwheels on ramps, then from under the car spray the front HC unit linkage system with any lubing & rust loosener.

An exhaustive workout on the height setting lever will then help working the lube into the linkage.

Once the HC works again, get under and spray with regular spray-grease to keep up the good effects of lubing.

PS : while you are there, treat the rear HC as well for preventive measures ...

DickieG · Post by **DickieG** » 07 Apr 2007, 20:28

Was the steering set with a degree of lock on it at the time the oscillating occured? If so then this is normal on Xantia's.

AndersDK · Post by **AndersDK** » 07 Apr 2007, 20:46

DickieG wrote:Was the steering set with a degree of lock on it at the time the oscillating occured? If so then this is normal on Xantia's.

Details on why is very welcome Dickie

Mandrake · Post by **Mandrake** » 07 Apr 2007, 21:46

AndersDK wrote:
DickieG wrote:Was the steering set with a degree of lock on it at the time the oscillating occured? If so then this is normal on Xantia's.

Details on why is very welcome Dickie

Unfortunately Dickie is correct

Most Xantia's will oscillate at the front on full lock - turning to full lock puts a lot of twist on the front strut rubber blocks due to the (poor) McPherson strut geometry - and increases the breakout friction of the strut movement (due to high side thrust on the ram bushes) enough to cause the height to constantly oscillate.

This even applies to struts that are well lubricated, and struts which are already sticky to begin with will do this oscillation much more certainly than well lubricated ones.

All 3 of our Xantia's do this. Another thing which compounds this problem which doesn't happen with the BX is that because the rollbar link is attached to the strut rather than the lower arm like the BX, when you turn the steering to full lock this causes the height corrector to make a spurious increase to the height - which can then trigger a series of oscillations.

(A BX strut probably still oscillates on full lock due to increased bearing thrust, but will not do so without an initial triggering change in height)

I should mention that a very sticky strut which is badly in need of lubrication (one that lurches during lifting) can also exhibit this behaviour in a straight ahead condition - so it could be a sign the struts need some lubrication.

GS and CX never suffered from these problems due to double wishbone design.

Another thing that will do it for sure is sideways thrust on the front suspension - the classic example is to lift the suspension to full height, then jack the front of the car off the ground for servicing, then lower the car to the ground and set the suspension to normal height - because the wheels were placed on the ground while at maximum height, due to geometry there is now a high side thrust on the bearings at normal height and breakout friction is again increased - causing oscillating.

This is most likely what the original poster experienced - the solution is simply to let the car roll forward/backward a little bit when it is as near as possible to normal height, and it will stop oscillating.

(This "problem" did also exist on GS and CX - due to the wishbones moving in an arc, although to a much lesser degree due to less friction of movement under load for the wishbones than McPherson struts)

Another way to think about this issue is that it is like any negative feedback system with hysteresis - it will oscillate if the hysteresis of the servo device (suspension height) is greater than the hysteresis of the sensing device. (height corrector)

More hysteresis of the height corrector linkage will actually make it LESS likely to oscillate, and there is a small amount of deliberate hysteresis built into the height corrector and height corrector linkage for this reason.

(In the GS it was done much simpler - deliberate slack between the steel ball on the end of the height corrector and the flat metal fingers that press on either side of it)

Too much hysteresis of the height corrector will make height corrections inacurate though due to a large dead band, while not enough will make it prone to oscillate if there is the slightest extra friction in suspension movement.

Regards,
Simon

deian · Post by **deian** » 07 Apr 2007, 22:32

Thats a very educated answer simon, never seen it happen on my car yet, but tomorrow i may test it for fun. Your knowledge of hydractive suspension or even hydraulics/engineering is very good, I like reading your replies! Can I ask what you do for a job in real life (away from Citroen suspensions

)?

AndersDK · Post by **AndersDK** » 08 Apr 2007, 02:50

And too much hysteresis will render the HC inactive ...
So much for that bit. What I actually meant was the HC overshooting in a snatching way because of a sticking linkage. That will teach me trying to do it too popular in terms.

Nice learning about the steering to lock behaviour. Believe we have had it up before, but I certainly was blank on this Xantia phenomen. Never seen it on any Xantiae doing parking manouvres where you are going real slow and steering to lock. Not even on my in-laws Xantia regularly visiting my BX'es ...
And he will have to do his steering to lock manouvers to get nose front leaving my yard ...

I dont believe its the problem here ...

BTW : try lift a (normal height) BX one side to change a wheel. That makes for strange behaviours too ...

DickieG · Post by **DickieG** » 08 Apr 2007, 06:39

AndersDK wrote:Never seen it on any Xantiae doing parking manouvres where you are going real slow and steering to lock. Not even on my in-laws Xantia regularly visiting my BX'es ...
And he will have to do his steering to lock manouvers to get nose front leaving my yard ...

The chances are that you won't see it when doing parking manoeuvres as the car needs to be set with a fair degree of lock on for some time. You'll have to engage the in-laws in conversation at a critical time in their manoeuvering

Mandrake · Post by **Mandrake** » 08 Apr 2007, 06:46

Hi Anders,

AndersDK wrote:And too much hysteresis will render the HC inactive ...
So much for that bit. What I actually meant was the HC overshooting in a snatching way because of a sticking linkage. That will teach me trying to do it too popular in terms.

I know what you mean... a sticking linkage will indeed cause overshooting, but probably not oscillating, it tends to overshoot and then stop IMHO.

Nice learning about the steering to lock behaviour. Believe we have had it up before, but I certainly was blank on this Xantia phenomen. Never seen it on any Xantiae doing parking manouvres where you are going real slow and steering to lock. Not even on my in-laws Xantia regularly visiting my BX'es ...
And he will have to do his steering to lock manouvers to get nose front leaving my yard ...

Next time the car is around, try turning the steering to full lock while stationary and wait a few seconds and you'll notice the height lift up by a good 30-40mm. Then return the steering to the centre and it will drop again after a few seconds. Bad design.

(It's because the top mounting point for the rollbar drop link turns around with the turning of the strut pulling the rollbar upwards - although I havn't tested it I'm sure a BX won't do this because the rollbar connects to the lower arm)

The oscillating on full lock doesnt always happen depending on a few factors - if you're on grass or gravel it usually wont happen, it has to be on concrete or tarmac. Also if you are moving forwards or backwards at the time, even slowly,it wont do it, you have to be stationary on a hard surface so the suspension can be "pinched".

Also if the struts are in good condition and well lubricated it sometimes wont do it.... mine only does it sometimes - usually after doing a full lock turn in a car park, and stopping in a park and leaving quite a bit of lock on the wheel - the full lock causes the height corrector to lift the height, and when you straighten the wheel it decides to drop the height a bit but there is still enough lock on the wheel to make the struts bind a bit - and it starts oscillating.

Just another Citroen quirk....

Regards,
Simon

jeremy · Post by **jeremy** » 08 Apr 2007, 08:48

I think the droplink is attached to the strut on the Xantia (and ZX) to give a bit of pre-load to the anti-roll bar as the steering is applied and so bring it into action a bit earlier - and with luck reduce roll and presumably allow a smaller anti-roll bar to be used - which should also improve the ride.

Hydropneumatic is very good for suspension when the car is traveling in a straight line - but in its basic form provides very poor roll control. The anti roll bar is used for this - but provides substantial springing force - both in individual wheel bump in a straight line and on cornering, probably to the detriment of the ride. Contrast this to BMC Hydrolastic which was linked front to back and so provided roll resistance on the main springs. (A similar system is used on the Citroen rallycar which still seems successful even in C4 form)

CypherPunk · Post by **CypherPunk** » 08 Apr 2007, 11:38

Thanks for you help, especially Mandrake, although in the end I’m not sure that the problem was quite that complex. Also it wasn’t a slow gentle oscillation, when the car dropped down; it dropped very quickly and slammed against the bump stops, it was so fast that when it first happened I thought that something major had snaped.

I tried moving the car backwards and forwards and straightening the wheels up to no avail, the car just kept pumping up and crashing down, it was so regular it was almost like clockwork.

I eventually noticed a strange sound coming from the engine bay, when the car dropped down a tapping sound started and when the car finally reached the correct high the sound stopped with a loud metallic click. After pulling the air box out I managed to trace this sound to the metal box that was attached to the accumulator sphere (I can’t remember the proper name) so I decided to drop the car down to it’s minimum height, turn the engine off and bleed the system using the pressure release screw.

When I turned the pressure release screw by a quarter of a turn, instead of making the usual gentle hissing sound it made a really high pitched screaming sound and quite a bit of LHM cane flowing from the overflow pipe on the top of the LHM tank, the good news is that once I re-pressurised the system the problem was gone.

Now I’ve got a couple of ideas about what could’ve been causing the problem, first off the LHM level is too high by the looks of it, would I been ok to just siphon some LHM out of the tank until it’s at the correct level and would this be responsible for the problem?

Secondly, I presume that the block attached to the accumulator sphere is responsible for controlling the pressure somehow, is it possible that this is damaged? This is more of a guess going by the noise it made when I bleed the system.

Also, the car doesn’t rise very smoothly and sometimes it’s impossible to get the back of the car to rise at all, if the suspension has been set to minimum. However, if the height lever is put into the normal position first, then, once the front suspension has reached the correct height, moved into the maximum position the rear suspension will spring into life and act normally. I noticed that the rod from the height lever is attached to the height corrector by a bent metal rod, is this normal?

Once again thanks for you help, you lot certainly know your stuff when it comes to Citroens.

AndersDK · Post by **AndersDK** » 08 Apr 2007, 12:33

That settles the steering to lock syndrome ...

No its not a problem at all having too high a level of LHM - other than it may give problems with your missus complaining over greasy spots on your driveway ...

You did not tell us the year of your Xantia V6 ?

The block which the accumulator sphere screws on to is the hydraulic system's pressure regulator (PR). Its responsible for keeping the system charged to the correct pressure.
From your description I think whats happened was a grain of dirt or debree lodged under the ballbearing valve in the PR, rendering it unable to close. Thus the PR would just exactly reach the upper cut-out pressure and then immediately cut-in again because of a rapid pressure loos. I've seen that on BX'es and CX'es too. A completely 'normal' problem.

Once you turned the pressure release (not the bleed) valve screw, the ballbearing valve seat was fluhed clean and everything back to normal.

Now you go out an siphon up some of the LHM, before missus makes a mess of you ....

thorter · Post by **thorter** » 08 Apr 2007, 12:44

If you clean out a height corrector and leave the end chambers dry of LHM, when the suspension is re-pressurised (at normal height setting), the height will drop and rise very like the symptoms described. This is to be expected, since the end chambers and the small jets provide the damping to stabilise the height feedback loop.

So it is possible that the symptoms were caused by a failing sphere (diaphragm leaking). This would probably be the accumulator to introduce gas into both ends of the height corrector. If the symptoms come back, this is a likely diagnosis.

AndersDK · Post by **AndersDK** » 08 Apr 2007, 13:06

thorter wrote:If you clean out a height corrector and leave the end chambers dry of LHM, when the suspension is re-pressurised (at normal height setting), the height will drop and rise very like the symptoms described. This is to be expected, since the end chambers and the small jets provide the damping to stabilise the height feedback loop.

So it is possible that the symptoms were caused by a failing sphere (diaphragm leaking). This would probably be the accumulator to introduce gas into both ends of the height corrector. If the symptoms come back, this is a likely diagnosis.

Yep

CypherPunk · Post by **CypherPunk** » 08 Apr 2007, 16:10

Sorry, it’s a 1997 Xantia V6.

I’ve just been for a blast round some country lanes and the difference with the new spheres is amazing, the back of the car is much harder to push down now but the ride is much better, I’ve always wondered if the old spheres weren’t the correct type and I’m now fairly sure I was right.

All of the spheres on the car are less that 4 months old and they were all brand new not re-gassed, so I can’t imagine it’s a leaking sphere causing the problem, however I’ll bear it in mind if the problem re-occurs.