anti sink sphere problems...

erez · Post by **erez** » 14 Dec 2005, 06:45

hi and good morning,
i replacled my anti sink sphere yesterday, and the xantia still sinks after i turn the engine off, what could be the problem?
i've been told that the anti sink sphere is the same as the main sphere, is that right?

thanx!
the car is xantia 2000cc 1997. (totally green!

)

Mandrake · Post by **Mandrake** » 14 Dec 2005, 07:15

How long does it take to sink, at the front, and the back ? How much does it sink ? How long does it take to lift again ?

Normally there should be no significant sinkage after 6-8 hours, and overnight its normal to lose approx 20mm of height at front and back but it should still not be completely down.

Regards,
Simon

pugxpert · Post by **pugxpert** » 14 Dec 2005, 08:05

anti sink not in spheres but located front one under lhm tank and rear one is next to rear brake accumalator,anti sink means exactly that it should not drop at all,happy sinking

AndersDK · Post by **AndersDK** » 14 Dec 2005, 09:46

pugxpert wrote:anti sink not in spheres but located front one under lhm tank and rear one is next to rear brake accumalator,anti sink means exactly that it should not drop at all,happy sinking

Please ...
Do not make such short comments as the content really is lost then

Its NOT a contest here of who knows best - and can post it first on the mark - in shortest form.

Erez :
The antisink spheres are basically the same type as the accumulator sphere. But they differ in pre-charge pressure from factory.
It's the antisink valves that prevents the car from sinking. Like anything else they can in fact fail and then the car still sinks.
However since the antisink valve is relying on the pressure differences in the suspension system there could be a number of other problems. I suspect you could gain a lot spending a Hydraquinage cure on your Xantia.

erez · Post by **erez** » 14 Dec 2005, 11:00

thank you all,
the rear end sinks about half way down in app. 2 minutes.
if you leave the car overnight (a long one) the front and the rear are completely down.
another problem is that when i start the engine, if i'm not pressing hard on the brake pedal, the rear end takes about 1 minute to get up,
and the front rises to full height! for about a minute.

TooMany2cvs · Post by **TooMany2cvs** » 14 Dec 2005, 12:19

erez wrote:the rear end sinks about half way down in app. 2 minutes.

Is it actually sinking, or is it just lowering to compensate for the fact that it has risen as the occupants have got out?

fastandfurryous · Post by **fastandfurryous** » 14 Dec 2005, 12:35

It sounds to me as if you have introduced a fairly large amount of air into the system, which is causing havoc.

Try Citaerobics (pumping the car from minimum to maximum several times) and bleed plenty of fluid from the brakes (use a long length of hose to return the bleed fluid to the LHM tank, means you can bleed several litres through the system)

It may also be that the system needs a good clean out.... when was the last time the LHM was changed?

pugxpert · Post by **pugxpert** » 14 Dec 2005, 13:23

i did not put info on here because i think i know best,and i certinaly am in no rush to get the first post i just wanted to point the bloke in the right direction,any way the centre rear sphere is an accumalator for rear brakes if system fails and has nothing to do with suspension,i think your car is sinking because the anti sink valve is not shutting off which is a common problem on xantia and xm.Also if the system had air in it the car would not lift.rear anti sink valve is located on rear subframe next to the brake accumalator sphere.and the front is located under the lhm resevoir.i hope this helps with your question EREZ and satifies anders that my explanation is not to short and i probbaly dont know as much as you !! regards.

AndersDK · Post by **AndersDK** » 14 Dec 2005, 13:57

pugxpert wrote:i did not put info on here because i think i know best,and i certinaly am in no rush to get the first post i just wanted to point the bloke in the right direction,any way the centre rear sphere is an accumalator for rear brakes if system fails and has nothing to do with suspension,i think your car is sinking because the anti sink valve is not shutting off which is a common problem on xantia and xm.Also if the system had air in it the car would not lift.rear anti sink valve is located on rear subframe next to the brake accumalator sphere.and the front is located under the lhm resevoir.i hope this helps with your question EREZ and satifies anders that my explanation is not to short and i probbaly dont know as much as you !! regards.

Now that's informative reading - like I wanna see it 8)

Clogzz · Post by **Clogzz** » 14 Dec 2005, 14:00

pugxpert...Could this be you Malcolm ?

TooMany2cvs · Post by **TooMany2cvs** » 14 Dec 2005, 14:32

pugxpert wrote:the centre rear sphere is an accumalator for rear brakes if system fails and has nothing to do with suspension

I'm not sure you're right on that.

Diravi XMs and CXs have a brake accumulator, but Xants and DirAss XMs certainly don't - and even if they did, it wouldn't be for the REAR brakes which do next-to-nothing anyway.

That extra sphere in the back of more recent Xants and XMs is the anti-sink sphere. It also has some input (but I don't really understand why) into ride quality.

pugxpert · Post by **pugxpert** » 14 Dec 2005, 14:58

in answer to 2 many 2cv's comments the centre rear sphere on a xantia holds a reserve of pressure for rear braking because if there is no pressure from the hp pump the anti sink valve kicks in as we all know hydro pneumatic rear braking systems are supplied through the rear suspension so if there is no suspension you have no rear brakes this is why it is a rear brake accumulator ,just confimfed in tech training documentation,hope that answers your querie

TooMany2cvs · Post by **TooMany2cvs** » 14 Dec 2005, 15:36

pugxpert wrote:in answer to 2 many 2cv's comments the centre rear sphere on a xantia holds a reserve of pressure for rear braking because if there is no pressure from the hp pump the anti sink valve kicks in as we all know hydro pneumatic rear braking systems are supplied through the rear suspension so if there is no suspension you have no rear brakes this is why it is a rear brake accumulator ,just confimfed in tech training documentation,hope that answers your querie

Hmmm - Not that I'm doubting you, but I wonder why Citroen's parts website (www.citroen-pr.net) shows one anti-sink valve with a sphere attached to it under "Hydraulics/Anti-Sink Valve"?

As we all know, the rear brakes on a hydraulic Citroen do nothing much at the best of times - why bother with a reserve for them but not the fronts?

erez · Post by **erez** » 14 Dec 2005, 15:44

thanx guys, i have a correction...
first, lhm was replaced two months ago.
second, after the sphere replacment yesterday, air was taken out through a screw near the main sphere, should i do anything else beside that?
i will try citaerobics, and bleeding the brakes.

i just checked, when i park the car, it's height is correct, when i shut the engine off, after 20 seconds, the rear just drops down fast.
and in the morning it taks about a minute to rise, is that air in the system?

jeremy · Post by **jeremy** » 14 Dec 2005, 16:04

I'm getting confused here - anti-sink sphere same as a main sphere? What is a main sphere?

As I understand it there are 3 basic types of sphere used - suspension spheres which have a damper in the neck (looks like a plate with a hole in the centre and some cutouts round the side) - Accumulator spheres with an open neck and no damper, and anti-sink which presumably are the same as accumulators with no damping but have a pipe fitting as well.

Pugexpert is quite right - anti sink function is dependant on the VALVE not the sphere. A/S cars have a relatively weak pump for the brakes and suspension and pressure drops in the system after the A/S valve as normal. When starting you get the situation of the A/S valve opening but there being insufficient high pressure LHM to sustain the suspension and power the rear brakes - so back can drop and there be no brakes. A/S sphere should discharge then and provide pressure.