xantia suspension diagnosis

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stevecritchlow
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xantia suspension diagnosis

Post by stevecritchlow »

Something with my 1997 2.1TD xantia suspension is not quire right, and I'd like to sort it befoe it becomes too much of a problem, but despite lots of reading I'm not really sure what the source of the problem is.
When parked up, the rear is sinking down further than it used too (looks at bit like a BX), and on start up is taking longer to rise than it used too. This is time dependent, i.e if the car has been parked five minutes theres no real problem and will rise in 5 seconds, but if parked for two hours it'll be well down on the back and will rise is about 15 seconds.
Any deas what might be wrong?
There doesn't appear to be any problem with the front suspension. Once the rear suspension has risen up there doesn't seem to be any problem in running, although as I'm new to citroen I'm not sure how good the ride should be. The LHM is clean and full.When running the car suspension up and down to max and miniumum heightslast weekend in an attempt to bleed any air, i found the car would rise up OK, and then sink down to its bottom travel, but then would not rise up again at all.
Does this info help anyone out there diagnose whats up?
steve
jeremy
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Post by jeremy »

Sounds like anti-sink valve to me. Don't think they are considered serviceable. I would suggest that a careful tap with a hammer might do something at least temporarily but there have been some postings on here about them bursting of their own accord so encouragement is not such a good idea.
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Post by Peter.N. »

It could be that the height control valve is sticking, a common problem. If you look on the rear anti roll bar you will find a clamp round it connected to some linkage, follow it and you will find the height control valve on the other end, give it several applications of WD40 over a few days which should unstick it. the easiest way to test the spheres, is to bounce each corner up and down with the engine running, you should have at least three or four inches of movement, if not the sphere on that corner needs changing, onl change them as pairs.
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Mandrake
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Post by Mandrake »

I'm surprised nobody suggested checking the anti-sink sphere. The way the rear anti-sink valve is designed (it's different to the front one) it relies partially on the pressure stored in the anti-sink sphere to keep the valve shut properly once the source pressure drops.
(The valve works on differential pressure not absolute source pressure)
If the anti-sink sphere is flat the leakage from the brake valve will cause the pressure at the anti-sink sphere and valve connection point to drop, which will allow the anti-sink valve to open again, until pressure from the rear suspension flows in to replenish it, the the valve will close again. In the process the rear suspension will drop a bit. This will probably happen many times until the back is right down.
(Basically the end result if the anti-sink sphere is dead flat is that the anti-sink valve might as well not be there...)
Have a look at the section on anti-sink in this very useful page:
http://citroen2.triger.com.pl/kc/pdf/citguide.pdf
As well as the anti-sink sphere acting as a brake accumulator when the anti-sink valve is closed, it is also there to provide a source of pressure for the brake valve to leak away that won't directly cause the suspension to drop.
Provided that the main accumulator pressure leaks away faster than the pressure at the anti-sink sphere, the valve will stay closed after it first closes, leaving the suspension completely isolated and preventing it from (quickly) going down.
If the anti-sink sphere is nearly flat the pressure will drop faster with brake valve leakage than the main accumulator pressure, causing the anti-sink valve to periodically open then close again when the pressure difference is equalized.
It is possible for the valve to stick, but I see it as unlikely, and difficult/expensive to replace in any case. On the other hand, the anti-sink sphere has a definate lifetime like any other sphere, and is easy to replace...(watch out for the pipe screwed into the end of it though, make sure that is undone before unscrewing the sphere itself from the mounting plate)
Regards,
Simon
jeremy
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Post by jeremy »

sounds reasonable to me Simon. To be honest as I haven't got it on my BX I've never really investigated it - must get Gabor's book out sometime and have a look!
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jeremy</i>

sounds reasonable to me Simon. To be honest as I haven't got it on my BX I've never really investigated it - must get Gabor's book out sometime and have a look!
jeremy
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
The link I posted last time only has simplified diagramatic pictures of the anti-sink valves, which do them a little injustice I think, the following link has proper technical drawings of them of the three different types: (not in english though!)
http://www.citrotech.se/data/pdf/xantia ... sc-mac.pdf
At first glance the anti-sink sphere only seems to fill the role of "emergency brake accumulator" so people think it is mis-named, but it does indeed seem to be intracately linked with the anti-sink function itself, and without it working properly the back does seem to sink like a non-anti-sink model...so maybe Citroen aren't as silly as we assume when they name things [:D]
Regards,
Simon
jeremy
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Post by jeremy »

Nice diagrams - I'll work my way through them eventually!
thanks
jeremy
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Post by c.morewood »

I've got a similar problem on my '99 Xantia estate, the rear settles down over 20 minutes after switching off the engine.
It was pointed out to me yesterday after the service, that I had a small weep of LHM from a manifold which all the high pressure pipes connect into (looks like item 9 on Swedish diagram which Mandrake provided, http://www.citrotech.se/data/pdf/xantia ... sc-mac.pdf)
Unfortunately my Swedish isn't as good as my Norwegian so I've no idea what a ventil "sc/mc" bak is.
Maybe Anders could translate?
Anyway I've an idea that this might be the problem and would like to replace it if I can find out what its called.
anybody any ideas?
Thanks
Chris
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