Evolution: Xantia Hydractive Suspension Regulation - Info

[white exec]

Well done in seeing all that through to a conclusion.
A combination of height corrector and rear brake condition, with a dash of non-standard sphere thrown in!

As with much on these cars, when difficult problems arise, it usually pays to return things to factory standard, and start from there.

This has been an enjoyable thread, so good luck with the car, and let is know how things continue.

[Mandrake]

Parts show the same doseur for Xan I and II, Saloon and Estate - 4860 11.

I stand corrected then.

[Armidillo]

Thanks guys for explaining this. In the last 12 months I have replaced front and rear rotors and pads on my Xantia SII wagon, and it now squats a little under brakes, which given how much bigger the rear disks are than on the hatchback model, seems hardly surprising!

I actually don't mind the sensation - it feels very planted and secure. However based on the above discussion, I believe I could pretty much eliminate this by fitting slightly more "bitey" front pads. Alternatively I could fit harder rear pads, although it seems counter productive to fit lower performance pads (although I suppose they would last longer).

Cheers
Alec

[xantia_v6]

A point that you may not be aware of is that the estates run with lower pressure in the rear suspension than the hatchbacks, and this flows through to lower rear brake pressure relative to the front, so the larger rear calliper pistons and pads on the estate bring the front/rear brakes back into balance.

[Armidillo]

Thanks Mike

I had assumed that the bigger rear brakes were specified because of the greater load carrying capacity, but I can see the logic that lower pressure and bigger brakes would cancel out. Of course if bigger brakes were fitted due to greater weight alone, you'd expect fronts to also be larger (which they are not).

However I must be missing something very basic in understanding this system - I would have assumed that because of the greater weight of the wagon (both Tare & GVM), with the extra weight being essentially behind the back seats, that rear suspension pressure would need to be higher to support the additional weight. Is there different valving somewhere (I believe the height correctors are identical between break & berline)? I know that the rear suspension spheres are different, but had assumed that was all to do with tuning the suspension damping for the differing weights.

[xantia_v6]

The rear suspension rams on the estate are larger diameter, hence lower hydraulic pressure is required for the same loading, which allows a bigger peak load.

[Armidillo]

Ah - thanks! Another non-interchangeable part then!

[blaueboot]

Well done in seeing all that through to a conclusion.
A combination of height corrector and rear brake condition, with a dash of non-standard sphere thrown in!

As with much on these cars, when difficult problems arise, it usually pays to return things to factory standard, and start from there.

This has been an enjoyable thread, so good luck with the car, and let is know how things continue.

After a very pleasant vacation (about 3000km spent in the car. And man.., those eastern-european roads are so lovely when driving a hydro-pneumatic car!) the rear is still staying down as it should.
Nevertheless the ride started to feel a bit harsher when I returned back home. Somehow stumbled across a thread here which addresses the 'microbubbles', and well..., I have them as well. And a lot of foam when lowering the suspension completely.
Temporary fix for now is, lowering the suspension right after stopping the engine. This makes sure the system purges of its pressure (and air), without sucking up the expelled air again. Next to that I also concluded that my pressure regulator has an internal pressure leak. Both problems will get a permanent fix and I will post about these in the correct topics when I get to it.

Back on topic about those Hydractive Regulator blocks...
Since it is hard to find the revised design (or at least it seems to me), I've always wondered if there isn't a way to modify the original design of the Hydractive Regulator. I've pondered about trying to drill the same kind of internal channels in the block, but that seemed quite impossible to me. A few days ago I suddenly thought about something...

The same effect of the revised blocks should be achievable via external piping. The only 'difficulty' is that one should be able to make his own 3,5mm hydraulic pipe since you'd need to make 2 short ones of those. And additionally you need to get your hands on an extra 3,5mm 'T-junction'.
So it's not an easy way of modifying.., but maybe an easier alternative than finding those rare Xantia HAregulators.

*attached is a lovely Paint generated schematic of what I mean.

[white exec]

Interesting to try to find an alternative way of achieving the improvement, using the existing valves.

There are two items missing from your suggestion, though:
- the strong biasing spring for the main shuttle valve, which defaults the system to reliable Soft;
- a direct and always-open pathway from the HA sphere to the electrovalve shuttle (and main shuttle), and which provides the important equal pressure either side of the main shuttle (providing stability and immunity to hydraulic shock from the road surface).

If you pull up Fig.4 (p.8 of the Citroen document), that shows the extra internal pathway, uninterrupted by the main shuttle.

[Wesa]

[attachment=1]I actually made this "evolution mod" by external pipe. My Activa project has been few years on idle but continued just few weeks ago.
This mod is now tested in rear suspension and seems to work perfectly.
Mod includes sphere adapter/extender with two additional M8 connection. One for the pipe and one for the air nipple. The valve spring is adopted from C5 regulator and plug behind is modified with stopper tap.
SC.MAC valve 5th connection plugged by blind plug.
In following link are some photos of this project: http://www.sitruunapatonki.fi/forum/vie ... 8&start=75.
I can share more photos and drawings if somebody is interested of it? Anyway it could better to being evaluated more widely before taking on roads.