Hydractive 2 damping tweaks ?

Mandrake · Post by **Mandrake** » 13 Aug 2005, 14:20

Hi All,
I recently replaced a faulty rear hydractive centre sphere on my 1997 VSX Xantia and sure enough the hard ride is gone, but now I'm finding that the rear is now actually TOO soft, and more importantly, underdamped.
It's reacting too much to acceleration, also on any kind of road with undulations the back is forever over-correcting and pitching the back of the car.
Doing a bounce test at the back by hand shows the body rebounds too quickly (in my opinion) and overshoots the rest position before returning.
By contrast my Dad's SX without Hydractive and standard 30 bar/1.1mm spheres at the back feels much more stable with almost perfect damping - still a soft ride, but no pitching or rocking at all on undulations.
Doing a bounce test on his SX shows a slower rebound with no overshoot at all... (eg close to critical damping)
Is there something wrong here or is the Hydractive 2 model deliberately tuned this way for a very soft ride at the back in the soft mode, at the expense of some overshoot ?
If so, has anybody experimented with alternative spheres for the hydractive centre with a damping valve in it to add a little bit of extra damping ?
The hydractive blocks have two damping valves in them with supposedly 1.1mm bypass holes, which are not adjustable, so I was thinking of perhaps trying a front sphere off a non-hydractive xantia, eg 50 bars, 1.5mm hole as a rear hydractive sphere, to add a moderate amount of extra damping.
Because the 1.5mm hole is somewhat bigger than the 1.1mm holes in the built in valves, the change should be noticable but not excessive.
As far as I know, all three rear spheres are on-spec after replacing the middle one, and I'm not happy with the resultant damping...[:(]
Is it possible that the damping valves in the hydractive blocks eventually wear out ? After all, they don't get replaced with the spheres, unlike the ones in all the other spheres...
Comments anyone ?
Regards,
Simon

bernie · Post by **bernie** » 13 Aug 2005, 14:42

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

Hi All,
I recently replaced a faulty rear hydractive centre sphere on my 1997 VSX Xantia and sure enough the hard ride is gone, but now I'm finding that the rear is now actually TOO soft, and more importantly, underdamped.<hr height="1" noshade id="quote"></blockquote id="quote">
That is exactly my symptom which prompted me to change to new spheres but as you know I'm still not there.
I'm making up the tester to go further.
As an experiment, Simon, I fitted front BX estate spheres to the back of mine and the ride was much better with better damping.

Mandrake · Post by **Mandrake** » 13 Aug 2005, 14:48

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

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

Hi All,
I recently replaced a faulty rear hydractive centre sphere on my 1997 VSX Xantia and sure enough the hard ride is gone, but now I'm finding that the rear is now actually TOO soft, and more importantly, underdamped.<hr height="1" noshade id="quote"></blockquote id="quote">
That is exactly my symtom which prompted me to change to new spheres but as you know I'm still not there.
I'm making up the tester to go further.
<hr height="1" noshade id="quote"></blockquote id="quote">
Wait a sec, I thought your problem was that the ride was hard and harsh ? (EG stuck in hard mode) Are you saying that you've now replaced the rear hydractive centre sphere and you now find it too soft and underdamped at the back ?
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
As an experiment, Simon, I fitted front BX estate spheres to the back of mine and the ride was much better with better damping.
<hr height="1" noshade id="quote"></blockquote id="quote">
Did you fit them as corner spheres or one of them on the hydractive centre sphere position ?
I don't have any complaints with the hard mode - its hard, yes, but its very well damped, and suitable for what it is - a mode to keep the roll down during hard cornering, etc, its only the soft mode I have a problem with.
Ironically, while I'm finding the soft mode too soft at the back, I'm finding the soft mode in the front not soft enough, (and a bit too firmly damped) but I havn't done a pressure test on the front centre hydractive sphere yet, nor have I greased the struts. (Which helped a LOT on Dad's car)
Regards,
Simon

bernie · Post by **bernie** » 13 Aug 2005, 15:30

My ride is hard and harsh but very under damped.
It bottoms out very easily.
I tried the BX spheres at the back corners and the ride was soft and floaty but still under damped. NO difference between hard or soft unfortunatly.
It is just plainly not right.

Kowalski · Post by **Kowalski** » 13 Aug 2005, 19:19

Is it possible that you have a front center sphere on the back by mistake? If you did, that would make the ride too soft.

Post by **Peter.N.** » 13 Aug 2005, 19:30

To have a harsh ride and too much suspension movement is a contradiction in terms as far as spheres are concerned, your harsh ride must be caused by something else such as tyre pressures, tyre type or suspension arm bearings.

bernie · Post by **bernie** » 13 Aug 2005, 19:37

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

Is it possible that you have a front center sphere on the back by mistake? If you did, that would make the ride too soft.
<hr height="1" noshade id="quote"></blockquote id="quote">
Out of the 8 spheres I bought at least 3 were wrong.
That's why I'm making a sphere tester.

bernie · Post by **bernie** » 13 Aug 2005, 19:40

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Peter.N.

To have a harsh ride and too much suspension movement is a contradiction in terms as far as spheres are concerned, your harsh ride must be caused by something else such as tyre pressures, tyre type or suspension arm bearings.
<hr height="1" noshade id="quote"></blockquote id="quote">
Believe me it's very harsh, not Citroen like at all.
The rear bump stops are almost non exsistant.

howiedean · Post by **howiedean** » 13 Aug 2005, 20:56

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

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Peter.N.

To have a harsh ride and too much suspension movement is a contradiction in terms as far as spheres are concerned, your harsh ride must be caused by something else such as tyre pressures, tyre type or suspension arm bearings.
<hr height="1" noshade id="quote"></blockquote id="quote">
Believe me it's very harsh, not Citroen like at all.
The rear bump stops are almost non exsistant.
<hr height="1" noshade id="quote"></blockquote id="quote">
I know my previous Xantia HDI estate was not hydractive but like yourself after changing the rear spheres it seemed too soft and would hit the end stops. My local Citroen indy suggested raising the rear height slighty which we did and it cured my problem.
I suspected that the spheres did not have the correct pressures in them but did not have access to a tester.
Regards

Mandrake · Post by **Mandrake** » 14 Aug 2005, 05:01

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

Is it possible that you have a front center sphere on the back by mistake? If you did, that would make the ride too soft.
<hr height="1" noshade id="quote"></blockquote id="quote">
No, it's definately 50 bars, not 75 [:D]. It's primarily a lack of damping, rather than being too soft springing wise. The rebound is too fast and overshoots the static position by nearly an inch then returns when I do a bounce test - a clear sign of not enough damping.
Now imagine this happening all the time while driving and you can see my problem...(it's enough to make some people sea sick, although I only find it annoying, since I know it can be much better....)
I think I will try a sphere with a damper valve and see what happens, and at least then I will be able to tune the damper valve hole to get optimum damping as well. Either the damping valves in the rear hydractive block are faulty/worn or Citroen have screwed up in tuning them [:(]
Regards,
Simon

alexx · Post by **alexx** » 14 Aug 2005, 11:39

Damper valve can be faulty (on the sphere or in the HA block)
In fact, several months ago I was tweaking with spheres on my (non-hydractive) car. I preferred the way they were tuned on older Citroens, meaning 1:1 bound:rebound damping ratio. On Xantia, rebound damping is higher, like on other cars with conventional suspension, so it doesn't "float" like I was used to.
Front spheres have 4 and rear 3 steel discs over main damper valves on the outer side, while there are 2 on inner side. It turned out that at least outer disc could be easily deformed towards out about 0.3-0.4 mm - not a very good steel. Now, front end, when pushed down, overshots the middle position by 0.5-1 cm, and rear by about 0.5 cm on return, about 2 times more than before the "adjustment". But, the car covered only about 65.000 km so far, so the damper valves were in good condition and the ride is still well damped now.
I don't recommend this kind of tweaking if the spheres were on the road much more, or drilling the central bore on the damper valve, because it can easily result in damping rate being too low.

Mandrake · Post by **Mandrake** » 14 Aug 2005, 12:33

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

Damper valve can be faulty (on the sphere or in the HA block)
In fact, several months ago I was tweaking with spheres on my (non-hydractive) car. I preferred the way they were tuned on older Citroens, meaning 1:1 bound:rebound damping ratio. On Xantia, rebound damping is higher, like on other cars with conventional suspension, so it doesn't "float" like I was used to.
<hr height="1" noshade id="quote"></blockquote id="quote">
Actually the rear spheres on the GS had different bound and rebound rates as well - the rebound direction was significantly stiffer than the bound direction, although the front spheres were symetrical.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
Front spheres have 4 and rear 3 steel discs over main damper valves on the outer side, while there are 2 on inner side. It turned out that at least outer disc could be easily deformed towards out about 0.3-0.4 mm - not a very good steel. Now, front end, when pushed down, overshots the middle position by 0.5-1 cm, and rear by about 0.5 cm on return, about 2 times more than before the "adjustment". But, the car covered only about 65.000 km so far, so the damper valves were in good condition and the ride is still well damped now.
I don't recommend this kind of tweaking if the spheres were on the road much more, or drilling the central bore on the damper valve, because it can easily result in damping rate being too low.
<hr height="1" noshade id="quote"></blockquote id="quote">
It sounds like you've done exactly the opposite of what I'm trying to do [:D] In the soft mode the bound and rebound rates seem about the same, it overshoots in both directions by at least 25mm.
On the other hand in hard mode there is no overshoot, and it is (deliberately) overdamped, while the rebound has quite a lot stiffer damping than the bound direction.
By contrast the rear spheres on my Dad's non-HA2 Xantia seem to have just the right damping, the ride is still quite soft, the rebound is moderately fast, but there is zero overshoot, and thats the tuning I'm trying to achieve.
On the front of his car we found it was originally a bit underdamped, and we reduced the damper bypass holes on the front spheres from the standard 1.5mm to 1.2mm, which seems to give critical damping.
Regards,
Simon

Mandrake · Post by **Mandrake** » 14 Aug 2005, 12:54

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

My ride is hard and harsh but very under damped.
It bottoms out very easily.
I tried the BX spheres at the back corners and the ride was soft and floaty but still under damped. NO difference between hard or soft unfortunatly.
It is just plainly not right.
<hr height="1" noshade id="quote"></blockquote id="quote">
Just a thought Bernie,
Have you tried greasing the front struts yet ? I finally got around to doing mine today (we did the ones on Dad's car a couple of months ago) and wow, what a difference. An immediately obvious reduction in harshness of ride in the soft mode, and also less fidgeting on uneven surfaces at around town speeds.
Although I'm sure you have other problems too, you should look at doing this as well. As I've noticed on my car that the problems have been a number of things adding up rather than one magic bullet.
Have a look at the following thread where I describe how I did it:
http://www.andyspares.com/discussionfor ... hichpage=1
Regards,
Simon

alexx · Post by **alexx** » 14 Aug 2005, 19:31

Simon, I think 25mm overshoot is far too much. From my remembering (when I was buying this car), hydractive Xantias in soft mode behave very similar to non-hydractive ones during the "bounce-test". In hard mode, they needed several seconds to sink under my weight (and similar time to return back).
I tried bounce test once more on my car and overshoot is really minor - several mm front and rear. Can't say for sure it's different than before mentioned modification, but ride is different.
And another thing - I didn't feel the difference between bounce and rebound damping force under my hand neither before nor now. It's questionable whether force produced by my weight is sufficient to disc valves even start opening, as they have some pretension. So, most of the fluid is going through the central bores, that obviously have 1:1 ratio. It was the same with BX I owned before, that had GS spheres fitted. This difference is felt during the drive.
According to one jpn site, CX and GS had "symetrical" spheres front and rear (same number of disc on inner and outer side), while XM had symetrical rear spheres. I hope data are correct (at least for Xantia they are), because the guy dismantled quite a number of different spheres.

Mandrake · Post by **Mandrake** » 15 Aug 2005, 03:49

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

Simon, I think 25mm overshoot is far too much. From my remembering (when I was buying this car), hydractive Xantias in soft mode behave very similar to non-hydractive ones during the "bounce-test". In hard mode, they needed several seconds to sink under my weight (and similar time to return back).
<hr height="1" noshade id="quote"></blockquote id="quote">
Yes 25mm is definately unacceptable overshoot, which is why I'm trying to do something about it. [:D] The trouble is, if all 3 spheres are correct pressures, what is left ? (Apart from the hydractive control block valves)
I don't have access to any other Hydractive 2 Xantia's to compare against, and even if I did, chances are they would be in far worse condition than mine, as very few people seem to bother to maintain the suspension or know whether it is in optimal working order or not...for most people its pretty much a case of taking it into the dealer when the sphere diaphrams pop and the ride suddenly goes hard, and trusting the dealer to do the right thing....(ha !)
Some people like a small amount of overshoot in the interests of softer ride but I prefer critical damping with no overshoot as I like the extra feeling of stability it gives.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
I tried bounce test once more on my car and overshoot is really minor - several mm front and rear. Can't say for sure it's different than before mentioned modification, but ride is different.
And another thing - I didn't feel the difference between bounce and rebound damping force under my hand neither before nor now. It's questionable whether force produced by my weight is sufficient to disc valves even start opening, as they have some pretension. So, most of the fluid is going through the central bores, that obviously have 1:1 ratio.
<hr height="1" noshade id="quote"></blockquote id="quote">
Yes thats true, however the rear in Hydractive hard mode is definately harder to lift than to push down, but this is probably only noticed due to the very small bypass bore.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
It was the same with BX I owned before, that had GS spheres fitted. This difference is felt during the drive.
According to one jpn site, CX and GS had "symetrical" spheres front and rear (same number of disc on inner and outer side), while XM had symetrical rear spheres. I hope data are correct (at least for Xantia they are), because the guy dismantled quite a number of different spheres.
<hr height="1" noshade id="quote"></blockquote id="quote">
According to my Dad (who was a Citroen mechanic in the 50's to 70's) the GS had assymetric damping at the rear, and having owned one and driven a number of them it sure seemed that way to me. You could push it down more easily than lift it up during a bounce test, while my Xantia (in soft mode) seems symetrical.
Not a very scientific test, sure... [:D]
Regards,
Simon