Having read several other Forum questions, it is plain to see that there are some bright sparks out there when it comes to the mysteries of the Citroen Suspension system... So here goes:
I have a 1996 Xantia Activa Turbo.
In the mornings I will find my car still up... i.e. the Anti Sink sphere is obviously functioning OK
On switching on I have to wait for about a minute (during which time the car stays up) for the "Stop" and "suspension" lights to go out (at which point I have power steering and brakes)
At this point the back of the car will often drop like a rock to its lowest position and over the next minute or so will slowly rise again to normal driving height.
All warning lights remaining unlit during this time.
Anyone got an idea where I should start to look to correct this.
P.S. no clicking from the pump either.
Plummeting Suspension
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blueboy2001
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When you start the engine, system must be pressurised, because overnight pressure in the part of the system usually drops to zero. It means that LHM gets into spheres, compressing nitrogen inside them, until the pressure is equilised.
In the case of Activa, it means that pressure in accumulator and one activa sphere should reach about 170 bar, and in other activa sphere half of that. If spheres are new, it's about 0.6 l of fluid. If spheres are almost flat, it can be more than 1 l. So I calculated.
On petrol engines with 6+2 pump, we have (theoretically) about 0.9 cm3 LHM per 1 engine revolution. At 1000 rpm, it means 0.9 l/min. So, if spheres are new, it will theoretically take 40 s, if they are old, more than a minute. That's one of the reasons, why I don't like Activas. On 'ordinary' models, only accumulator sphere have to be topped, and there's no additional leakage through the activa anti-roll system, so if the hydrailics is in good condition, in the morning there will be also some pressure left.
When anti-sink valve open, anti-sink sphere will also have to be pressurised. If it's new, it's pressure is near rear suspension's working pressure, so nothing happens (almost). If the pressure in it is low, it means almost 0.4 l of fluid. In that case, rear end will drop, because fluid from rear suspension is forced into anti-sink sphere, and you'll have to wait (theoretically) additional half a minute untill all is refilled again.
Of course, there could be some other problem(s), but check the spheres first.
This anti-sink sphere is somewhat obscure. Usual explanation is that it helps rear anti-sink valve to function properly, but I can't find physical explanation for that. While rear end is up, pressure in rear suspension and anti-sink sphere doesn't change, so nitrogen in anti-sink sphere can't expand and do anything usefull. I think it's main purpose may be to act as a pressure reserve for rear brakes, because their pressure suply - rear suspension - can be cut off by anti-sink valve, if something happens with pressure suply from pump and accumulator. But maybe I'm wrong.
Edited by - alexx on 20 Feb 2003 08:55:12
In the case of Activa, it means that pressure in accumulator and one activa sphere should reach about 170 bar, and in other activa sphere half of that. If spheres are new, it's about 0.6 l of fluid. If spheres are almost flat, it can be more than 1 l. So I calculated.
On petrol engines with 6+2 pump, we have (theoretically) about 0.9 cm3 LHM per 1 engine revolution. At 1000 rpm, it means 0.9 l/min. So, if spheres are new, it will theoretically take 40 s, if they are old, more than a minute. That's one of the reasons, why I don't like Activas. On 'ordinary' models, only accumulator sphere have to be topped, and there's no additional leakage through the activa anti-roll system, so if the hydrailics is in good condition, in the morning there will be also some pressure left.
When anti-sink valve open, anti-sink sphere will also have to be pressurised. If it's new, it's pressure is near rear suspension's working pressure, so nothing happens (almost). If the pressure in it is low, it means almost 0.4 l of fluid. In that case, rear end will drop, because fluid from rear suspension is forced into anti-sink sphere, and you'll have to wait (theoretically) additional half a minute untill all is refilled again.
Of course, there could be some other problem(s), but check the spheres first.
This anti-sink sphere is somewhat obscure. Usual explanation is that it helps rear anti-sink valve to function properly, but I can't find physical explanation for that. While rear end is up, pressure in rear suspension and anti-sink sphere doesn't change, so nitrogen in anti-sink sphere can't expand and do anything usefull. I think it's main purpose may be to act as a pressure reserve for rear brakes, because their pressure suply - rear suspension - can be cut off by anti-sink valve, if something happens with pressure suply from pump and accumulator. But maybe I'm wrong.
Edited by - alexx on 20 Feb 2003 08:55:12
Thanks for the information. But which spheres ( I've got a whopping 10 in my Activa) would you suggest are most likely to be knacked?
Blueboy is suggesting the Anti Sink, but my understanding (limited I grant you ) is that its function is to stop the from dropping overnight by slowly releasing fluid back into the system to account for any leakages. And, as the car does what it's supposed to do by staying up overnight, that would make ME think it was working OK.
Edited by - xactiva on 20 Feb 2003 13:26:02
Blueboy is suggesting the Anti Sink, but my understanding (limited I grant you ) is that its function is to stop the from dropping overnight by slowly releasing fluid back into the system to account for any leakages. And, as the car does what it's supposed to do by staying up overnight, that would make ME think it was working OK.
Edited by - xactiva on 20 Feb 2003 13:26:02
As I explained, if the pressure in anti-sink sphere is low, rear end of the car drops when rear anti-sink valve opens, as you noticed. So changing or recharging the anti-sink sphere will probably eliminate that - it was confirmed by several other members of this forum in previous posts. Also, as I said, I'm not sure that anti-sink sphere does what is named for, so if the car doesn't sink overnight, it doesn't mean that anti-sink sphere is ok, unless you know how old it is.
Other 3 spheres to be checked are accumulator sphere and both spheres of activa system, connected to hydraulic rams on roll-bars. If you renew them, the system will take less time to pressurize, but since there are 3 spheres insteand of 1 in non-activa models, you'll still have to wait about 2.5 times longer than owners of non-activas. According to my math, it will be about 40s at 1000 rpm.
If the car stays up overnight, renewing other 6 suspension spheres won't bring any difference here, as they are still on the 'working pressure' in the morning.
Of course, this is only a theory, as I don't own Activa. But hope it will be of some help.
Other 3 spheres to be checked are accumulator sphere and both spheres of activa system, connected to hydraulic rams on roll-bars. If you renew them, the system will take less time to pressurize, but since there are 3 spheres insteand of 1 in non-activa models, you'll still have to wait about 2.5 times longer than owners of non-activas. According to my math, it will be about 40s at 1000 rpm.
If the car stays up overnight, renewing other 6 suspension spheres won't bring any difference here, as they are still on the 'working pressure' in the morning.
Of course, this is only a theory, as I don't own Activa. But hope it will be of some help.
AHA
The light is begininning to dawn. Now you put it that way I understand what you were talking about Alexx.
Cheers.
I'll change that out straightaway.
As to the general pressurising thing, I had a regular Xantia ( not even Hydractive) before and that never took much time at all to pick its skirts up.
Your Maths makes a whole lot of sense in that regard.
For a supposedly "quick" car my Activa would be rubbish for getaways. But it IS a really great handling car through the twists and turns, although often a little too firm in the back end over holes etc when it just drops you down them.
Also those new sleeping policemen that you have to straddle (where they've blocked one side of the road off) are very uncomfortable unless you get them completely even as the Activa seems to think you're leaning into a corner and stiffens the whole lot up.
Anyway...Rambling now.. Thanks again for the help. I'll post the results.
The light is begininning to dawn. Now you put it that way I understand what you were talking about Alexx.
Cheers.
I'll change that out straightaway.
As to the general pressurising thing, I had a regular Xantia ( not even Hydractive) before and that never took much time at all to pick its skirts up.
Your Maths makes a whole lot of sense in that regard.
For a supposedly "quick" car my Activa would be rubbish for getaways. But it IS a really great handling car through the twists and turns, although often a little too firm in the back end over holes etc when it just drops you down them.
Also those new sleeping policemen that you have to straddle (where they've blocked one side of the road off) are very uncomfortable unless you get them completely even as the Activa seems to think you're leaning into a corner and stiffens the whole lot up.
Anyway...Rambling now.. Thanks again for the help. I'll post the results.
Hi,
Having only had my Activa for 3 weeks it's a pretty new experience after owning 16v BX's for the last three years-the suspension on them seems,dare I say it,straightforward by comparison.
I have noticed that mine does take a few seconds in the morning for the lights to go off,but nothing like the time that's been outlined.I reckon 20 secs and I'm on my way.However,when I went to put fuel in yesterday I watched the car drop a couple of inches at the rear and then rise again almost immediately,could this indicate that I should replace my anti sink aswell before I start suffering the problem mentioned?
Also,I have to agree that for a car that rides amazingly at high speed on the motorway and goes round bends on rails,the low speed ride is,well,crap to be honest! Can't believe that a company like Citroen did not address this problem before the car was released.
Oh well,apert from that I love it.
Cheers
Mike
Having only had my Activa for 3 weeks it's a pretty new experience after owning 16v BX's for the last three years-the suspension on them seems,dare I say it,straightforward by comparison.
I have noticed that mine does take a few seconds in the morning for the lights to go off,but nothing like the time that's been outlined.I reckon 20 secs and I'm on my way.However,when I went to put fuel in yesterday I watched the car drop a couple of inches at the rear and then rise again almost immediately,could this indicate that I should replace my anti sink aswell before I start suffering the problem mentioned?
Also,I have to agree that for a car that rides amazingly at high speed on the motorway and goes round bends on rails,the low speed ride is,well,crap to be honest! Can't believe that a company like Citroen did not address this problem before the car was released.
Oh well,apert from that I love it.
Cheers
Mike
Well, I had in mind the time needed to completely pressurize the system, when the regulator finally cut off. It's approximated anyway. Of course, warning light will go off earlier. And, if the car is already on the correct height, there's in fact no need to wait the system to fully pressurize.
As this system pressurizing is a dynamic process, I think (but not quite sure) that the time, when the light goes off, depends also on the spheres' condition. Some more remarks from Activa owners would be appreciated.
There can be also some other reason, why warning light stays too long. One possibility is leakage of the roll-bar hydraulic rams (some reports about that on this forum) or some other hydraulic element. Anyway, it's really worth checking those 2 spheres, connected to that rams, because they act as dampers for roll-bars, which are VERY thick on Activa. If they are flat, the ride over uneven surface, such as those sleeping policemen, will be uncomfortable (to much shaking from left to right).
You can also check (and comment) my thoughts about hydropneumatic and hydractive suspension in my previous posts.
http://www.andyspares.com/discussionfor ... IC_ID=2444
http://www.andyspares.com/discussionfor ... IC_ID=2503
I hope I didn't mislead you (and someone else).
Report the results. There's not much written about activa suspension anyway.
Alex
As this system pressurizing is a dynamic process, I think (but not quite sure) that the time, when the light goes off, depends also on the spheres' condition. Some more remarks from Activa owners would be appreciated.
There can be also some other reason, why warning light stays too long. One possibility is leakage of the roll-bar hydraulic rams (some reports about that on this forum) or some other hydraulic element. Anyway, it's really worth checking those 2 spheres, connected to that rams, because they act as dampers for roll-bars, which are VERY thick on Activa. If they are flat, the ride over uneven surface, such as those sleeping policemen, will be uncomfortable (to much shaking from left to right).
You can also check (and comment) my thoughts about hydropneumatic and hydractive suspension in my previous posts.
http://www.andyspares.com/discussionfor ... IC_ID=2444
http://www.andyspares.com/discussionfor ... IC_ID=2503
I hope I didn't mislead you (and someone else).
Report the results. There's not much written about activa suspension anyway.
Alex
first off alexx is spot on about the 'anti sink' sphere,it is in fact a rear brake accumulator sphere and its function is to supply the brake control valve with pressure if the line pressure drops in the rear suspension (since the rear suspension supplys the rear brakes).without it if the suspension pressure dropped the anti sink valve would close and there would be no pressure available to the rear brakes. second,the things on the anti roll bars are not dampers,they are roll correction actuators which jack up or pull down on the bars to alter their stiffness to combat roll,there is one on each a/roll bar fitted diagonally opposite to each other(n/s/f & o/s/r) .the 2 extra spheres (on top of the regular hydractive) are not connected directly to the actuators,one is for the roll stiffnes regulator and the other is a seperate accumulator sphere for that circut to even out fluctuations in the fluid flow.
WOW! It's amazing how much you can learn in just one day.
Having taken on board everything people have said on here and on other posts with regard to similar topics, I have discovered a much held misconception with regard to Anti Sink:
There are anti sink VALVES and an anti sink SPHERE, each of which performs a different task.
My car did not sink when turned off because the VALVES were working perfectly in isolating the suspension spheres from the rest of the hydraulic system thus not allowing them to sink.
The anti sink SPHERE (feeding the rear braking circuit) is also isolated when the VALVE closes and in theory maintains pressure in that system until the pump is running again.
When the car is restarted and sufficient pressure is built up to open the security valve (another one associated with the pump, front brakes and steering) the anti sink VALVE opens and, if everything was working smoothly, finds a nice healthy pressure in the rest of the system with the suspension already pumped up (It never went down see)and just carries on seamlessly.
However, if the anti sink SPHERE is duff and there is no pressure in that line, then the simultaneous opening of the rear circuits means that the pressure in the rear SUSPENSION suddenly gets diverted to balance the system up (dropping the rear) and needs to be pumped up again.
Now if that's wrong then .......
Anyway, I reckon I'd better change that sphere.
Also my stiff rear suspension might seem to be the linkages that need freeing/lubricating.
Any ideas on good places to start there (It's an Activa remember) or clues as to previous Forum threads.
Edited by - xactiva on 21 Feb 2003 08:08:05
Having taken on board everything people have said on here and on other posts with regard to similar topics, I have discovered a much held misconception with regard to Anti Sink:
There are anti sink VALVES and an anti sink SPHERE, each of which performs a different task.
My car did not sink when turned off because the VALVES were working perfectly in isolating the suspension spheres from the rest of the hydraulic system thus not allowing them to sink.
The anti sink SPHERE (feeding the rear braking circuit) is also isolated when the VALVE closes and in theory maintains pressure in that system until the pump is running again.
When the car is restarted and sufficient pressure is built up to open the security valve (another one associated with the pump, front brakes and steering) the anti sink VALVE opens and, if everything was working smoothly, finds a nice healthy pressure in the rest of the system with the suspension already pumped up (It never went down see)and just carries on seamlessly.
However, if the anti sink SPHERE is duff and there is no pressure in that line, then the simultaneous opening of the rear circuits means that the pressure in the rear SUSPENSION suddenly gets diverted to balance the system up (dropping the rear) and needs to be pumped up again.
Now if that's wrong then .......
Anyway, I reckon I'd better change that sphere.
Also my stiff rear suspension might seem to be the linkages that need freeing/lubricating.
Any ideas on good places to start there (It's an Activa remember) or clues as to previous Forum threads.
Edited by - xactiva on 21 Feb 2003 08:08:05
Yes, your conclusions are correct, or at least that's what I think.
But, there's more. 'Anti-sink sphere' will maintain pressure in rear brake circuit if brake dosieur valve is in good order. Unfortunately, it's a little underdimensioned device. There are 3 slide valves inside the latest, 'XM-type' version. First regulates front brake circuit. If it's worn, there will be regular clicking from HP pump/regulator, even with new accumulator sphere. So I changed it on my BX. It was about 100 EUR + labour. Other two slide valves regulate rear brake circuit. When they are worn, rear end of the car without anti-sink valves sinks fast (several hours or even minutes). If there's anti-sink (and it works), the rear won't sink, but the pressure in anti-sink sphere will soon drop. So it may happen, when you change the anti-sink sphere, that it won't totally eliminate rear end drop.
Fortunately, this wear in dosieur valve parts measures in 1/1000 mm, so braking function is not affected. Anyway, the pressure is high, so it's enough to permit significant internal leakage.
About anti-roll system, there are not many parts, but it's quite complex to understand. I looked at the schema again. It's components are:
- front stabilizer with hydraulic ram
- one sphere, directly connected to pressure supply (170 bar) and to one side of that hydraulic ram
- rear stabilizer with hydraulic ram
- one sphere, connected to one side of that hydraulic ram via stiffness regulator, so this connection can be cut off if ECU decides so.
- roll corrector (very similar to height corrector), attached to front suspension legs.
One side of both rams IS directly connected to pressure supply (at least on the scema in the Citroen guide of Mr. Nastasic). Other side gets pressure via roll corrector, which keeps the car upright.
But there's more. Stifness of the roll-bars is higher than in non-activa models: 2.6 x on the front, 2 x on the rear! So, without additional damping, the ride would be uncomfortable. As I (and Mr. Nastasic) understand this, two spheres really acts like a sort of suspension for roll-bars, killing their stifness when going straight. But, on sharper bends, stifness regulator, driven by the ECU, cuts off one sphere, disabling that additional damping of both spheres, and roll-bars become rigid. In addition to that, front activa sphere also evens out pressure supply fluctuations (from 145 to 170 bar), like Wheeler said.
That's how I understand this.
Edited by - alexx on 21 Feb 2003 08:24:36
But, there's more. 'Anti-sink sphere' will maintain pressure in rear brake circuit if brake dosieur valve is in good order. Unfortunately, it's a little underdimensioned device. There are 3 slide valves inside the latest, 'XM-type' version. First regulates front brake circuit. If it's worn, there will be regular clicking from HP pump/regulator, even with new accumulator sphere. So I changed it on my BX. It was about 100 EUR + labour. Other two slide valves regulate rear brake circuit. When they are worn, rear end of the car without anti-sink valves sinks fast (several hours or even minutes). If there's anti-sink (and it works), the rear won't sink, but the pressure in anti-sink sphere will soon drop. So it may happen, when you change the anti-sink sphere, that it won't totally eliminate rear end drop.
Fortunately, this wear in dosieur valve parts measures in 1/1000 mm, so braking function is not affected. Anyway, the pressure is high, so it's enough to permit significant internal leakage.
About anti-roll system, there are not many parts, but it's quite complex to understand. I looked at the schema again. It's components are:
- front stabilizer with hydraulic ram
- one sphere, directly connected to pressure supply (170 bar) and to one side of that hydraulic ram
- rear stabilizer with hydraulic ram
- one sphere, connected to one side of that hydraulic ram via stiffness regulator, so this connection can be cut off if ECU decides so.
- roll corrector (very similar to height corrector), attached to front suspension legs.
One side of both rams IS directly connected to pressure supply (at least on the scema in the Citroen guide of Mr. Nastasic). Other side gets pressure via roll corrector, which keeps the car upright.
But there's more. Stifness of the roll-bars is higher than in non-activa models: 2.6 x on the front, 2 x on the rear! So, without additional damping, the ride would be uncomfortable. As I (and Mr. Nastasic) understand this, two spheres really acts like a sort of suspension for roll-bars, killing their stifness when going straight. But, on sharper bends, stifness regulator, driven by the ECU, cuts off one sphere, disabling that additional damping of both spheres, and roll-bars become rigid. In addition to that, front activa sphere also evens out pressure supply fluctuations (from 145 to 170 bar), like Wheeler said.
That's how I understand this.
Edited by - alexx on 21 Feb 2003 08:24:36