XM rear suspension

FrenchLeave · Post by **FrenchLeave** » 19 Jan 2005, 22:05

My last posting seems to have gone astray so here goes again.
Car is a 1999 XM V6 auto with 61000 miles on. Super car, but within a minute of stopping the engine the rear suspension has collapsed to its lowest level. Car has had hydro flushing fluid in for past 1000 miles, but this hasn't cured it. I suspect the anti sink valve but having laid under the car (not easy at 72!) I can't locate the darned thing. I can only see one central sphere when I expected to see two (one anti sink, one hydractive). There is a valve thingy up alongside the levelling valve, and another on the right hand side of the car. My wife says the car looks like a praying mantis. Any advise from you experts out there would be much appreciated.

Post by **RichardW** » 20 Jan 2005, 01:55

Rapid sinking of hydractive cars is due to failure of an internal O ring in the hydractive valve. I think the valves can be repaired - try giving Plaeides a ring - they're near Cambridge. There should be 4 spheres under the rear. The anti-sink sphere has only small pipe going into the back of it. The hydractive centre sphere is screwed directly onto the valve block AFAIK.

Dave Bamber · Post by **Dave Bamber** » 21 Jan 2005, 01:34

http://www.pleiades.uk.com/

Niek · Post by **Niek** » 21 Jan 2005, 03:19

The anti-sink sphere is located next to the rear left wheel. But it is quite high up and slightly to the front of the wheel. You won't be able to do anything about it without removing the rear and middle exhaust boxes.

alexx · Post by **alexx** » 21 Jan 2005, 03:55

I'm not sure that XM with V6 engine had anti sink system fitted - a member of our local forum reported that his mechanic didn't find rear anti-sink sphere either on his XMV6 mkII ('95 I think - or '97 - not quite sure). Unless it's different on RHD cars

NiSk · Post by **NiSk** » 21 Jan 2005, 14:01

My '98 XM 2.5TD Break definitly has some form of anti-sink, but it only has 7 spheres (incl. accum), so I guess that the anti-sink valve is incorporated in the rear HA-sphere assembly?
//NiSk

alexx · Post by **alexx** » 21 Jan 2005, 15:38

I think it isn't, at least not in Hydractive Xantia - it's a separate element, connected with HA assembly with several pipes

DoubleChevron · Post by **DoubleChevron** » 21 Jan 2005, 15:48

Anti-sink is only a valve ??
Don't you have the main accumulator, front hydractive, rear hydractive, and rear brake accumulator.
That's my understanding anyway. The anti-sink is only valves, not spheres.
seeya,
Shane L.

FrenchLeave · Post by **FrenchLeave** » 26 Jan 2005, 03:11

Thank you all for your help so far, I've also downloaded the XM spares catalogue so I'll be able to recognise what I'm looking for. Now plucking up courage to run my beauty up on ramps and slide under again, this time I'll take a digicamera to record the scene for posterity.

Niek · Post by **Niek** » 27 Jan 2005, 02:04

No, anti-sink is not only a valve. There are two valves (front and rear) and an extra sphere at the rear. How it all works still puzzles me.
The valves (mechanical) close when the pressure of the accumulator sphere decreases to less than the pressure left in the suspension (struts??) hence sealing them off from the rest of the system, retaining the pressure and preventing the car from sinking. This would mean that if you've got worn struts, the car would still sink. The extra sphere at the rear is there because the brake-valve leaks so much that the rear would still always sink, with this sphere it outlasts the acc. sphere.
But of-course this is all theory, I've never seen it explained by Citroen and there are several versions of how it should all work.
My car now only sinks at the front (worn struts perhaps?) but the extra sphere has never been replaced yet (10 years, 225000 km) so I doubt that it will still do anything at all. Maybe replacing it will stop the front from sinking, shredding the above theory...[xx(]

alexx · Post by **alexx** » 27 Jan 2005, 02:42

"Anti-sink sphere" is only a supplemental accumulator for rear brakes, it's not needed for the anti-sink system to work properly. Explanation in Nastasic's Citroen guide about leaking doser valve is wrong.

FrenchLeave · Post by **FrenchLeave** » 06 Feb 2005, 18:36

Here's the update so far. I located the anti sink valve, it's fairly accessible about a foot to the right of the height regulator, mounted vertically between the suspension cross tube and the lateral exhaust silencer (I never did find the "anti sink" sphere!). But after poring over the system diagrams I became convinced that there had to be a major leak through another component downstream to account for the rapid suspension collapse and the obvious suspect was the brake valve. Thank you Dave Bamber for your lead to the Pleiades web site, they confirm the brake valve as the probable culprit. So I'm off to see them tomorrow (they are only 50 miles away).
Best wishes to all

dan.2cv · Post by **dan.2cv** » 06 Feb 2005, 20:05

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

"Anti-sink sphere" is only a supplemental accumulator for rear brakes, it's not needed for the anti-sink system to work properly. Explanation in Nastasic's Citroen guide about leaking doser valve is wrong.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
With regards to the anti sink -
My Xantia will raise itself back up to normal height half way through a fuel refill without the engine running. I assumed the anti sink worked in conjunction with the height corrector so that when the height fell it opened the anti sink vave and allowed high pressure fluid from the anti sink circuit (still pressurised by the AS sphere) to raise the car back to normal height.
If the sphere played no part, where would the pressure (or 'push') come from to raise the car without the pump running?

bernie · Post by **bernie** » 06 Feb 2005, 20:33

My BX does the same (no extra sphere) when fuelling up.
The pressure comes from the accumulater sphere.

dan.2cv · Post by **dan.2cv** » 06 Feb 2005, 20:41

Well that's that theory then!!