Rear end sinks when engine not running

[Stempy]

Even when on max height the rear end of the Xant sinks within a few minutes of switching the engine off. It's had a rear accumulator within the last year, could I be looking at replacing the anti sink valve? It stays where its put all the time the engine is running and the dog bone seems ok.

[Old-Guy]

It does sound as though it's the anti-sink valve, but the Anti-Sink Spere (a.k.a. Rear Accumulator) plays a vital part by providing pressure to ensure that the ASV closes properly, especially when the car is lightly loaded. An alternative could be that one of the rear rams is leaking back to the reservoir excessively.

As it's such an easy job, if you haven't done it already, I'd bleed the rear brakes to flush out any old fluid and dirt lurking in the rear brake lines that might be causing problems - especially if there's any gas/air in the rear system which could be pushing the same bit of crud back to jam the ASV partly open. Of course the ASV could simply be stuck open as it only closes when the engine stops and re-opens when the STOP warning goes out.

As you'll see from the Anti-sink Suspension section of The Citroën Technical Guide the rear suspension and rear brakes are intimately linked by the rear hydraulics. The Guide may help you work out where the problem lies.

[Xaccers]

All the rear spheres play a roll in keeping the anti sink valve closed, if some are low then the valve won't shut and the back sinks.
If your car has hydractive but is soft when running then it is likely the firmer corner spheres need replacing.

The a/s sphere is there to provide brake pressure when the pump is not running as the closed a/s valve isolates the rear from the front accumulator sphere.
Without it if your aux belt snapped you'd have no rear brakes.

[niva44]

I had the same problem with my XM after the spheres were replaced, I opened the bleed valve half a turn to release any air, I heard the air hissing out in less than 2 seconds ,re-tightened the valve and the problem has been solved.

[Old-Guy]

Good point! I took it as read that whoever changed the A/S sphere knew what they were doing and thoroughly bled the rear brakes as part of the job - absolutely essential and very easy.

[Stempy]

These are very valid points as when I think about it the problems began when I changed the rear electrovalve so I bet it's just trapped air, although I did bleed the brakes at the time I was in a hurry and probably didn't do a very thorough job. As for knowing what I'm doing, well 99% of my life is guesswork, the other 1% I just make up as I go along........