Xantias "jumping" front ends - solution !

[CitroJim]

I believe this is caused by the anti-sink valve coming into play during a rapid suspension movement due to the pressure in the front suspension being higher than the mainline pressure which may be low due to a worn accumulator or a pressure regulator that's cutting out at too-low a pressure. Only way to tell, if you know the accumulator is OK, is to plumb in a test gauge and check the regulator cuts out at 170 bar...

You can often see the same thing happen on a hydractive car when the car is rising or falling on the manual height lever - at some point the front may leap and is caused by a high pressure demand momentarily lowering main system pressure enough to shut the anti-sink valve.

It never happens at the rear because of the anti-sink sphere acting as a reserve of pressure and the rear suspension having generally much lower pressure in it.

[HDI]

The accumulator is most likely ok as it was replaced less than 2 years ago. I'll live with it for now as it doesn't cause any other problems. Thanks for the info though.

[albertz78]

Hi Guys, I have purchased the control lever along with the rubber seal and dog bone connector. Can anyone post a relatively simple guide to fitting?

[lancia58]

Hi Vince

Do you remember if you could visually see that the bar is deformed and bent?

Thanks
Zohar

[Mandrake]

Replying to an old post here...but it caught my eye.

You can often see the same thing happen on a hydractive car when the car is rising or falling on the manual height lever - at some point the front may leap and is caused by a high pressure demand momentarily lowering main system pressure enough to shut the anti-sink valve.

Actually I don't think this has anything to do with the anti sink valves Jim, it only happens on Hydractive models for a start...

If you're referring to having the suspension sitting on maximum height for a while, particularly if the engine is turned off for a period, then lowering the height, only to have one or both ends (but typically the front) pop up like a cork after the height has gone down, then re-correct.

This is the Hydractive valve sticking in hard mode. As you know it takes pressure differential between the source pressure and suspension pressure to push the valve into the soft mode - when the suspension is in maximum height mode there is no positive pressure differential between the source and suspension, in fact if the engine is left off for a while it can become negative (more pressure in the suspension) pushing the valve to the hard position.

This isolates the Hydractive regulator sphere and even when you start the engine and lower the suspension it tends no stay stuck in hard mode for quite a while. The reason for this is because to go back to soft mode the shuttle valve has to move in the direction of the regulator sphere, eg push more oil into that sphere. Because its in hard mode the outer spheres are isolated so the oil can't flow there.

However because the regulator sphere has 170 bars in it and is tightly compressed there is no room for more oil to flow in without the pressure rising above the source pressure, so the shuttle valve gets kind of jammed, it has full pressure on both sides but almost no compressible medium to push against so it stays stuck in the hard position. (It can't move the necessary distance to switch whilst still keeping the regulator sphere pressure below the source pressure)

After a while the gradual leakage of pressure through the closed regulator valve from the regulator sphere to the outer two strut spheres allows the pressure to drop enough that the valve moves and WOOSH, it switches over to soft mode suddenly and spontaneously and the car springs up like a cork as the pressure rushes from the regulator sphere to the struts...

Although this is the mechanism by which it happens I'm sure, it's unclear to me whether its a "normal" consequence of the design, or whether it requires some stickyness of the shuttle valve to occur...(in other words a greater than anticipated pressure differential is required to move the valve)

It certainly occurs in both my Hydractive Xantias, and I see it as one of those Citroen quirks that are nothing to worry about...