I would ask about this crazy idea in one of my ongoing topics for my Xantia restoration project, but I thought this is something others might be asking. Hopefully the information in this thread helps someone else.
I am locked in stiff mode, and I am in the process of diagnosing things, also properly modifying the harness (taking photos and documenting the process, which I'll share once successful).
In the meantime, I want to enjoy the Xantia at least a bit! Currently driving the Audi of my better half. Not a bad car at all, but Xantia is a much better car for the route I take daily.
Anyway, I thought about simply fitting the non-hydractive spheres I have at hand on the corners. I'm crimping watertight AMP Superseal type connectors on the electrovalve supply lines from the Hydractive control unit. Until I fix the Hydractive and verify it's working correctly, I'll be unplugging those connectors for my daily drive to prevent Hydractive somehow "waking up" from its coma.
Now, I believe both the hydractive and non-hydractive Xantias have a line between two wheels of each axle. So, when the rear left wheel hits a bump, some LHM is transferred to the right side, and vice versa. With the Hydractive in stiff mode, not only the center sphere is blocked out of the circuit, but this connection is also blocked, leaving each corner sphere take its own wheel's movement.
By fitting non-hydractive spheres at the corners, I'm hoping I'll have some benefit of the non-hydractive car. The route is a slow-ish urban route, school and office runs daily. No high speed motorways, no "spirited mountain passses".
Crazy idea? Will it cause any critical issues? Will it be noticeable? How do you all think?
Xantia Hydractive locked in stiff mode: Using non-hydractive spheres?
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octinum
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xantia_v6
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Re: Xantia Hydractive locked in stiff mode: Using non-hydractive spheres?
It is OK to fit non-hydractictive spheres. As long as the valves stay in firm mode it will behave just like a non-hydractive car.
I think it is still better to revert to the original specification when you can get it working.
I think it is still better to revert to the original specification when you can get it working.
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octinum
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Re: Xantia Hydractive locked in stiff mode: Using non-hydractive spheres?
Working on it! After the day's work and making up a story based on Stargate to convince a 10-year old pre-teen who says the day is too short to sleep that she needs to sleep, I took the tools and went to the car... Only to find out that I took the wrong connectors with me. Too late to get back once again at 11pm. 
The actual plan is to first crimp matching connectors between the Hydractive control unit side and the vehicle side (eventually the EV side). Both connectors will have double-crimped wiring, effectively adding two pigtails on either side. This should give me the ability to add and remove diodes at will, test the VN05Ns with a P21W bulb while separated from the electrovalves, and test the electrovalves for resistance and manually supplying with a fused line momentarily. Oh, also, two LEDs to the cabin somewhere to track H2 status in the future, or perhaps as inputs to some STM Blackpill if I ever get around it. In a few years' time, it seems, between work-kid-dog duties.
The only disaster is that, the shop might have forgotten to salvage the rear hydractive block on the donor car I had. I still have a heap of parts that I need to organize, but I wasn't able to find it last night. I found what I think is a front hydractive block, but the solenoid connector was broken to nothing. I might be able to access the terminals by carefully using the Dremel, which would be great progress. As for my own system, my initial tests indicate that the front electrovalve on my car is fine with 4.x Ohms of resistance, but I haven't been able to reach a conclusion on the rear one. I *think* it reads a short circuit, which could be the internal diode failing short, or something with the vehicle wiring. I'll have the car on the lift on Friday, and will measure the resistance directly on the electrovalves. At this point, I'm reasonably convinced that my issue is electrical. At which point(s), I don't know.
Anyway, I found a previous topic on this, but not using the spheres I intend to, and couldn't find the effects. What I'm expecting is:
- Close to non-hydractive on symmetric irregularities, where both the left and right wheels on each axle compress or extend more or less equally. This does not require any crossflow between the two sides of an axle, and the non-hydractive sphere should behave like what it is. I think slight asymmetric irregularities would be unnoticeable.
- Less body roll due to severely restricted (or maybe completely cut-off) crossflow. Mandrake's posts say crossflow with the hydractive car is cut-off, as the bypass only allows when the height corrector is doing correction, and hydractive blocks the main crossflow piping completely in stiff mode
- More side-to-side rocking on asymmetric irregularities than the non-hydractive Xantia, like when the right wheel hits a bump, due to the same "less body roll" reason above
Overall, I would have a Frankenstein similar to a softly sprung spring-and-damper car with the Xantia also relying on the anti-roll bar to control roll, without the crossflow. The ride should be much more comfortable than the A3 due to progressive and soft suspension, longer suspension travel, longer wheelbase, more independent rear suspension (twist beam on the A3 versus trailing arms on the Xantia), and wheels with slightly taller sidewals as well as lower unsprung weight.
At least, that's what I am hoping.
The actual plan is to first crimp matching connectors between the Hydractive control unit side and the vehicle side (eventually the EV side). Both connectors will have double-crimped wiring, effectively adding two pigtails on either side. This should give me the ability to add and remove diodes at will, test the VN05Ns with a P21W bulb while separated from the electrovalves, and test the electrovalves for resistance and manually supplying with a fused line momentarily. Oh, also, two LEDs to the cabin somewhere to track H2 status in the future, or perhaps as inputs to some STM Blackpill if I ever get around it. In a few years' time, it seems, between work-kid-dog duties.
The only disaster is that, the shop might have forgotten to salvage the rear hydractive block on the donor car I had. I still have a heap of parts that I need to organize, but I wasn't able to find it last night. I found what I think is a front hydractive block, but the solenoid connector was broken to nothing. I might be able to access the terminals by carefully using the Dremel, which would be great progress. As for my own system, my initial tests indicate that the front electrovalve on my car is fine with 4.x Ohms of resistance, but I haven't been able to reach a conclusion on the rear one. I *think* it reads a short circuit, which could be the internal diode failing short, or something with the vehicle wiring. I'll have the car on the lift on Friday, and will measure the resistance directly on the electrovalves. At this point, I'm reasonably convinced that my issue is electrical. At which point(s), I don't know.
Anyway, I found a previous topic on this, but not using the spheres I intend to, and couldn't find the effects. What I'm expecting is:
- Close to non-hydractive on symmetric irregularities, where both the left and right wheels on each axle compress or extend more or less equally. This does not require any crossflow between the two sides of an axle, and the non-hydractive sphere should behave like what it is. I think slight asymmetric irregularities would be unnoticeable.
- Less body roll due to severely restricted (or maybe completely cut-off) crossflow. Mandrake's posts say crossflow with the hydractive car is cut-off, as the bypass only allows when the height corrector is doing correction, and hydractive blocks the main crossflow piping completely in stiff mode
- More side-to-side rocking on asymmetric irregularities than the non-hydractive Xantia, like when the right wheel hits a bump, due to the same "less body roll" reason above
Overall, I would have a Frankenstein similar to a softly sprung spring-and-damper car with the Xantia also relying on the anti-roll bar to control roll, without the crossflow. The ride should be much more comfortable than the A3 due to progressive and soft suspension, longer suspension travel, longer wheelbase, more independent rear suspension (twist beam on the A3 versus trailing arms on the Xantia), and wheels with slightly taller sidewals as well as lower unsprung weight.
At least, that's what I am hoping.
xantia_v6 wrote: 29 Sep 2026, 00:53 It is OK to fit non-hydractictive spheres. As long as the valves stay in firm mode it will behave just like a non-hydractive car.
I think it is still better to revert to the original specification when you can get it working.
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octinum
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Re: Xantia Hydractive locked in stiff mode: Using non-hydractive spheres?
I'll add to captain's log in my car's topic, but let me drop this here in case someone else benefits.
Keep in mind that Jeffie (placeholder name for my Xantia
) was in storage for 3 years, stuck at highest setting all this time. So it might not be working as it should. The shop owner specifically asked me to drive the car daily for a couple weeks to "exercise" it.
Currently, all spheres are up to correct pressure, with the rear corner spheres definitely being non-hydractive. For the fronts, I wasn't present when they removed them to check and recharge one of them, and the markings are not visible on the topside. I'll try to find a way to read the markings, but I think the front is quite easy to push down when the EVs are not supposed to be energized. Then again, this is the only Hydractive Xantia I am familiar with, and also may be the only Xantia that is being restored to original spec as best as I can, so I can't compare.
The rear feels stiffer than I expected when I push down. It definitely is stiffer than the fronts, even when the EV is supposed to be energized. Again, this might mean it needs some exercise, so more to come later.
For now, with the electrovalves connected, I do feel some underdamped ride, but not dangerously so up to 90kph which I tried. I don't know how to describe it, but it feels like it moves up and down once or twice after I pass bumps like expansion joints at speeds up to 90kph, but the motion is nothing like violent bounces. Where I noticed underdamping is at sections with much less pronounced undulations, which produce some pitching motion seemingly with no reason. One would need to be paying attention for this tho, I don't think a passenger would notice.
Without the electrovalves disconnected, the car behaves similarly with the magnitude of the second motion reduced. The "seemingly out-of-nowhere" pitching motion is completely eliminated, which is what gave me the impression of underdamped ride in the connected state.
The difference is not too big on the short route I tried. It might become more noticeable at other road conditions, which I'm hoping to test this week on my regular daily route.
As for lean, I didn't notice anything scary in either state. But do note that I'm being perhaps overly cautious as I haven't driven the car for some time. I'll increase my cornering speeds gradually as I remember how the Xantia behavs.
Keep in mind that Jeffie (placeholder name for my Xantia
) was in storage for 3 years, stuck at highest setting all this time. So it might not be working as it should. The shop owner specifically asked me to drive the car daily for a couple weeks to "exercise" it. Currently, all spheres are up to correct pressure, with the rear corner spheres definitely being non-hydractive. For the fronts, I wasn't present when they removed them to check and recharge one of them, and the markings are not visible on the topside. I'll try to find a way to read the markings, but I think the front is quite easy to push down when the EVs are not supposed to be energized. Then again, this is the only Hydractive Xantia I am familiar with, and also may be the only Xantia that is being restored to original spec as best as I can, so I can't compare.
The rear feels stiffer than I expected when I push down. It definitely is stiffer than the fronts, even when the EV is supposed to be energized. Again, this might mean it needs some exercise, so more to come later.
For now, with the electrovalves connected, I do feel some underdamped ride, but not dangerously so up to 90kph which I tried. I don't know how to describe it, but it feels like it moves up and down once or twice after I pass bumps like expansion joints at speeds up to 90kph, but the motion is nothing like violent bounces. Where I noticed underdamping is at sections with much less pronounced undulations, which produce some pitching motion seemingly with no reason. One would need to be paying attention for this tho, I don't think a passenger would notice.
Without the electrovalves disconnected, the car behaves similarly with the magnitude of the second motion reduced. The "seemingly out-of-nowhere" pitching motion is completely eliminated, which is what gave me the impression of underdamped ride in the connected state.
The difference is not too big on the short route I tried. It might become more noticeable at other road conditions, which I'm hoping to test this week on my regular daily route.
As for lean, I didn't notice anything scary in either state. But do note that I'm being perhaps overly cautious as I haven't driven the car for some time. I'll increase my cornering speeds gradually as I remember how the Xantia behavs.
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xantia_v6
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Re: Xantia Hydractive locked in stiff mode: Using non-hydractive spheres?
I am not sure if it is relevant here, but hydractive and non-hydractive sphere have different damper specifications, so just increasing the pressure on a hydractive sphere will not make it behave correctly as a non-hydractive sphere.
Can you read the part numbers on your spheres to see what they started life as?
Can you read the part numbers on your spheres to see what they started life as?
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octinum
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Re: Xantia Hydractive locked in stiff mode: Using non-hydractive spheres?
Oh correct, I just noted that part to avoid you and our fellows here thinking sphere pressure in response to the stiffer-than-expected rear.
I think the Hydractive spheres both have lower pressures than the non-hydractive ones, and more restrictive damper leaf-springs as well as a narrower bypass hole. In fact, I think dampers have a bigger impact on how Hydractive behaves; the difference in pressure seems small especially on the rears. Or, better said, it's the spring-damper combinations.
I drove the car with Hydractive electrovalves energized today for a 30-odd km trip. Max speed was around 100kph and reporting all good for a steady ride. For anyone reading here, BEWARE that I didn't encounter any need for evasive maneuvers, so no comment there. I also pushed a bit at a couple bends, and I have quite a lot of grip.
I think the Hydractive spheres both have lower pressures than the non-hydractive ones, and more restrictive damper leaf-springs as well as a narrower bypass hole. In fact, I think dampers have a bigger impact on how Hydractive behaves; the difference in pressure seems small especially on the rears. Or, better said, it's the spring-damper combinations.
I drove the car with Hydractive electrovalves energized today for a 30-odd km trip. Max speed was around 100kph and reporting all good for a steady ride. For anyone reading here, BEWARE that I didn't encounter any need for evasive maneuvers, so no comment there. I also pushed a bit at a couple bends, and I have quite a lot of grip.
xantia_v6 wrote: 12 Oct 2026, 04:12 I am not sure if it is relevant here, but hydractive and non-hydractive sphere have different damper specifications, so just increasing the pressure on a hydractive sphere will not make it behave correctly as a non-hydractive sphere.
Can you read the part numbers on your spheres to see what they started life as?