Hydractive 2 damping tweaks ?

alexx · Post by **alexx** » 15 Aug 2005, 14:26

About GS (CX, BX), it's possible that damping characteristic wasn't exactly 1:1 although number and thickness of inner and outer disc was equal - they could be fitted with different pretension - whether they were slightly conical in shape, or valve seat was conical. Doesn't matter anymore, I sold BX almost 2 years ago...
About HA2, there are several hydractive Xantia owners on this forum, it would be fine if someone could tell something about behaviour in soft mode.
If damper valves in HA block are faulty, fitting a corner sphere, refilled to correct pressure would help. But, that won't solve the problem of car being underdamped when shaken from left to right side on asymmetrical bumps. This problem is present on all hydropneumatic Citroens, because left and right suspension cylinders are connected, and I really don't like it (conventional suspension is significantly better here). On HA, these pipes are much larger, but there are damper valves in between. If they are faulty, car will still be unpleasantly shaking from one side to other on uneven road.
If you like the ride in non-hydractive Xantia, worst case scenario would be completely eliminating HA system, which could turn out to be less expensive and time consuming job than tracing the problem here
On ordinary car you could simply replace the dampers and problem solved...

Mandrake · Post by **Mandrake** » 18 Aug 2005, 14:20

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by alexx
About HA2, there are several hydractive Xantia owners on this forum, it would be fine if someone could tell something about behaviour in soft mode.
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Yeah,
Come on all you Hydractive 2 owners, speak up! [:)]
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
If damper valves in HA block are faulty, fitting a corner sphere, refilled to correct pressure would help. But, that won't solve the problem of car being underdamped when shaken from left to right side on asymmetrical bumps. This problem is present on all hydropneumatic Citroens, because left and right suspension cylinders are connected, and I really don't like it (conventional suspension is significantly better here). On HA, these pipes are much larger, but there are damper valves in between. If they are faulty, car will still be unpleasantly shaking from one side to other on uneven road.
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I don't think they are "faulty" as such, as I don't notice any excessive side to side motion. Even in soft mode the roll is still less than non-HA models, and the stability about the rocking axis seems normal to me. It's only in the up-down direction I notice a lack of damping.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
If you like the ride in non-hydractive Xantia, worst case scenario would be completely eliminating HA system, which could turn out to be less expensive and time consuming job than tracing the problem here
<hr height="1" noshade id="quote"></blockquote id="quote">
No thanks. It's hardly a "simple job" to do that, because as you point out because of the large cross connecting pipes, it relies on the damper valves in the HA blocks to limit sideways flow, so disabling the hydractive system doesn't really solve that problem.
Besides... I specifically bought the car because it DID have Hydractive 2, and I'm not about to give up now that I have it working 80% as well as I think it should be. The basic system works fine its just the tuning of the damping doesn't quite suit my tastes, and I'm trying to establish for certain whether its a fault or just that they havn't tuned the damping the same way as the standard models...
All things considered, trying a sphere with a valve in it is relatively easy to do...
Regards,
Simon

pete_wood_uk · Post by **pete_wood_uk** » 26 Aug 2005, 17:53

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Mandrake

Come on all you Hydractive 2 owners, speak up! [:)]
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Sorry it took me so long - I was away, then forgot [:)] .
Bouncing the rear of my wife's 2000 HDI HA2 estate, I get a good squidge several inches down, then a very firmly damped rebound with almost no overshoot. If there's any overshoot at all then it's certainly less than the inch that you quote. This is an estate, mind you; I could imagine that the saloon is not intended for carrying the same loads (certainly doesn't have the same overhang behind the back wheels, so the lever arm is less) and so may be more lightly damped.
Looking at the sphere application table off of our hosts website (http://www.gsfcarparts.com/downloads/sphere_table.pdf) I notice that it just specifies 400/40 for the estate rears without specifying a damping factor. That'll be a mistake, then [:)]. However, I notice that the estate rears are 400/40, and so will be softer than the 400/30s that are listed for the hydractive saloon.
Also, I note that the list just says "hydractive" - I've no idea if Cit changed things between HA1 and HA2.
Best regards
Pete

Mandrake · Post by **Mandrake** » 26 Aug 2005, 18:10

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by pete_wood_uk

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Mandrake

Come on all you Hydractive 2 owners, speak up! [:)]
<hr height="1" noshade id="quote"></blockquote id="quote">
Sorry it took me so long - I was away, then forgot [:)] .
Bouncing the rear of my wife's 2000 HDI HA2 estate, I get a good squidge several inches down, then a very firmly damped rebound with almost no overshoot. If there's any overshoot at all then it's certainly less than the inch that you quote. This is an estate, mind you; I could imagine that the saloon is not intended for carrying the same loads (certainly doesn't have the same overhang behind the back wheels, so the lever arm is less) and so may be more lightly damped.
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Presumably you're quoting it in the "soft" state with engine running ? And if you turn the engine off with doors closed for 30+ seconds it becomes much stiffer with even more damping ? (Just checking that your rear hydractive sphere isn't popped, putting it in hard mode all the time....)
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
Looking at the sphere application table off of our hosts website (http://www.gsfcarparts.com/downloads/sphere_table.pdf) I notice that it just specifies 400/40 for the estate rears without specifying a damping factor. That'll be a mistake, then [:)]. However, I notice that the estate rears are 400/40, and so will be softer than the 400/30s that are listed for the hydractive saloon.
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Only assuming the arms have the same leverage lengths and that the piston area is the same, neither of which is the case as far as I know. (The piston diameter is different for sure)
Yes, that is a mistake in the table, there will be damping valves in those spheres.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
Also, I note that the list just says "hydractive" - I've no idea if Cit changed things between HA1 and HA2.
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Hydractive 1 was never used in the Xantia, so no problem there...
Hmm, not sure what to take out of the comparison with an estate, due to the differences in spheres, arms, pistons etc...but thanks anyway
Regards,
Simon

pete_wood_uk · Post by **pete_wood_uk** » 30 Aug 2005, 13:31

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Mandrake
Presumably you're quoting it in the "soft" state with engine running ? And if you turn the engine off with doors closed for 30+ seconds it becomes much stiffer with even more damping ? (Just checking that your rear hydractive sphere isn't popped, putting it in hard mode all the time....)
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Yes. Well, engine wasn't running, so's I could hear the solenoids to be sure, but yes, it was in soft mode. And yes, it's much much harder when the ECU cuts off the power to the solenoids after 30s with the doors shut.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
....Only assuming the arms have the same leverage lengths and that the piston area is the same, neither of which is the case as far as I know. (The piston diameter is different for sure)
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That I didn't know.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
Hmm, not sure what to take out of the comparison with an estate, due to the differences in spheres, arms, pistons etc...but thanks anyway
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Oh well, it was a simple experiment [:)]. Hopefully someone with a HA saloon might reply as well...
Cheers
Pete

Post by **RichardW** » 30 Aug 2005, 16:16

I could reply, but mine (97 TD VSX Hatch) isnt't exactly the most shining example of how Hydractive is supposed to work! It seems to take a while to get into soft mode, but when it does the ride is really floaty, like a BX on brand new spheres, but not really noticed the rear being oversoft - but then I think it needs new spheres at the rear (it's 8 years / 70k old, and I don't think they've been replaced). It's very hard in hard mode - I notice it being hard and fidgety coming round a roundabout just before I get to work, but it doesn't do it everyday. I also usually get very rapid sinking at the rear afterswitch off (although it doesn't seem to have been doing this as much lately, and the front height corrector seems to be working better too), and then it tends to stay in hard mode for the first 1/2 mile of driving before it switches into soft mode, when the rear sinks and it goes soft (presumably it sinks too low really, and then corrects back up, but you can feel the rear go down, and it gets much softer - I know where it happens leaving the house and work, same place every day!). I'll try it when I get home tonight, engine running, to see what it feels like. No point in doing it with the engine off, since it dumps all the pressure!
I might change the LHM for Hydraflush this weekend, but I'm not that bothered as it goes OK, and I only intend keeping it till next summer.

Mandrake · Post by **Mandrake** » 30 Aug 2005, 17:20

Thanks to Bernie's replies in another thread it looks like its relatively easy to take the damper valves out of the hydractive block (at least on the rear one) so rather than try fitting a sphere with a damper valve, I might first try tweaking the built in damper valves.
(The advantage of this is that tightening the damping in the built in valves will also reduce roll and side to side rocking in the soft mode, whereas a valve in the sphere wouldn't....also it means there wont be a non standard sphere involved, so next time that sphere is due to be changed it can be replaced with a standard sphere)
Assuming that the damper bypass holes are 1.1mm (the only information I have stating the hole size is not in english, so I'm reading between the lines a bit [:)]) then based on other sphere damper valve tuning I've done in the past, I've estimated that reducing the hole size to 0.9mm (a 40% reduction in hole area) should have the desired effect.
Fingers crossed...if that doesn't have the desired effect then I will try a sphere with a damper valve in it.
Regards,
Simon

bernie · Post by **bernie** » 30 Aug 2005, 19:05

I suggest welding the HA block damper hole (x2) and then redrilling the hole, if you can find 0.9mm bit