Xantia HDI rear spheres?

[HDI]

What is the function of the centre sphere on a basic Xantia HDI 90?
I've just replaced the rear suspension spheres but the ride height is not stable. The rear takes a long time to react to the ride height lever and over a matter of about 10 minutes sinks when driving normally.

[elma]

The rear sphere is an accumulator sphere for the rear brakes. Did you bleed the lhm system when you changed the sphere. I'd have thought your problem was air in the lhm system or a leak.

[HDI]

I went through the Citrobics routine after replacing the spheres and opened and closed the pressure relief screw a few times, it's worked in the past. Definitely no leaks.

[elma]

I'd suggest trying the full bleed procedure. It is described well here.

[HDI]

From what I can see in those instructions, there is nothing I haven't done, except for bleeding the rear brakes. Also, it says the middle rear sphere is anti sink. If thats the case I reckon that could be the problem.

[myglaren]

It is called an anti-sink sphere but that is not its function.
As James says, it is an accumulator to power the rear brakes. The anti-sink valve is connected to it though so bleeding the rear brakes may be the simplest answer to the problem.
Worth doing to eliminate that.

[CitroJim]

The middle so-called 'anti-sink' sphere is mis-named... It has nothing to do with sinking and has no effect on suspension action..

It is purely a rear brake accumulator to provide a reserve source of pressure to the rear brakes when the rear anti-sink valve is closed for any reason. Hence i's (wrong) name!

The only effect it can have is if it ruptured it can bleed its remaining nitrogen into the hydraulic system and cause a lot of entrained air to be present and that can upset the suspension... Citarobics will resolve it for a while, as will a good rear brake bleed.

For legal reasons the anti-sink sphere should be maintained in good condition for proper rear breake performance under all conditions...

The MOT states that a hydraulic Citroen like the Xantia must be able to make 6 full brake applications after the engine has been switched off with reserve pressure alone... This means both accumulators must be in good nick..

[xantia_v6]

I've just replaced the rear suspension spheres but the ride height is not stable. The rear takes a long time to react to the ride height lever and over a matter of about 10 minutes sinks when driving normally.

If the ride height is not stable with the engine running, then the most common problems are that the plastic dog-bone to the height corrector has come off at one end, or the metal rod clamped to the roll bar is broken. Either could have been coincidentally triggered while you had the car jacked up.

[HDI]

Checked all that, all ok.

[xantia_v6]

Clamp loose on roll bar?

[HDI]

Nope, all good.

[Mandrake]

What is the function of the centre sphere on a basic Xantia HDI 90?
I've just replaced the rear suspension spheres but the ride height is not stable. The rear takes a long time to react to the ride height lever and over a matter of about 10 minutes sinks when driving normally.

Is it also slow to react to changes in load at the back, like sitting in the boot ?

If so then most likely the height corrector linkage mechanism is rusted and/or partially seized up. This is typically due to rust between the spring loaded lever arm and the main bracket causing lots of drag.

This restricts how far the height corrector can move in response to the roll bar moving as the linkage spring allows the seized mechanism to not move when it is seized. (All the motion is lost in the spring) If it can't move far then it doesn't open much and the reaction of the height corrector is considerably delayed, and when it does react the ride height will only adjust slowly.

Sometimes the pivot itself wears out until it has a lot of slop in it then it will start binding.

Another possible cause is the damper valve inside the height corrector is clogged up with muck. The damper is just a series of small washers with pinholes in the middle of them separated by spacers.

You could try a grease gun into the moving linkage especially the main pivot with the spring on it then work it back and forth, but if that doesn't work you'd probably have to remove the whole assembly and strip it down to free it up. If you're going to that trouble you might as well open the height corrector and clean it out too especially the damper passages.

[HDI]

You may have something there. I noticed all of the height corrector linkages, springs etc were bone dry. Not corroded particularly, just dry of any grease. I gave them a good dousing in spray grease. The front system works fine though, despite having been sans lubricant. I'll give the rear height corrector some manual manipulation, maybe that will help. The LHM needs changing too, I noticed it was a nasty yellow colour when I removed the rear spheres. It has been partially changed by virtue of replacing the lost fluid, but it needs purging through. This car is showing signs of having been neglected.

[white exec]

If the LHM looks poor, and there are suspicions of dirt or neglect, get hold of 1x 5L of Hydraurincage, and run the car on that for 3000 miles, before refilling with LHM. It does an excellent job in cleaning the system.

[HDI]

That stuff is expensive!! I think I'll just purge and refill with new LHM and see how that goes!
Just tried to remove the accumulator sphere, which should have been a 5 minute job, but no!! Using an 18" pipe wrench the thing would not budge!! So, I'll have to try with my 24" pipe wrench, which isn't here at the moment, sod's law! I'm using sphere's off my Xantia SX which I'm using as a donor vehicle as it was written off in a shunt. They popped off that with almost no effort! Grief knows why they are so tight on this LX! The rears took two of us to remove, one holding the ram in one pipe wrench and the the other to move the sphere with another pipe wrench. Even using all the effort we could muster they only just moved! That was on a ramp with full access! Prior to that I tried the impact method with a cold chisel and big hammer, all that did was almost cut through the sphere!