Xantia rear anti sinking sphere and riding comfort

lancia58 · Post by **lancia58** » 10 Apr 2011, 17:34

Hi

I don't know if it is related but after stopping the engine if I push the rear of the car downwards it immediately sinking in compare to the front of the car that when pushing it downwards after stopping the engine it will bounce back to the riding height. Does this indicate that the rear anti sinking sphere is failed ? Although it is new it was manufactured on 2004 ( the manufacturing date is stamped on it ) . I don't know if a sphere has a limited shelf life . Can a failed anti sink sphere stiffen the rear suspension ? The sphere is I.F.S.H
P.S. I replaced it and the two rear spheres two weeks ago

Thanks
Zohar

Post by **CitroJim** » 10 Apr 2011, 17:53

Nope, the rear antisink sphere has no connection with sinking whatsoever

It is there to act as an auxillary rear brake accumulator to provide a reserve of pressure to the rear brakes when the rear anti-sink valve is closed; normally the rear brake pressure is supplied from the rear suspension circuit.

It is called an antisink because it was a necessary addition when the SC/MAC anti-sink system was fitted.

Rear sinking is primarily caused by flat and/or ruptured rear corner spheres.

It can also occur due to a flat main accumulator.

The antisink sphere cannot cause a hard ride either...

lancia58 · Post by **lancia58** » 10 Apr 2011, 18:14

Hi Jim

If the main accumulator is flat wouldn't it affect the front suspension as well ? The front suspension is OK ? When it is flat I know there is a ticking but no ticks at all . I replaced the main accumulator and the front spheres 7 months ago ( also I.F.S.H ). BTW at that the main accumulator was ticking

Thanks
Zohar

Post by **CitroJim** » 10 Apr 2011, 18:25

No, strangely it rarely affects the front..

If you've not swapped the rear corners then these are the most likely culprits. I tested a couple of unknown rear corners the other day and found one low and the other ruptured. This would not have caused a solid rear but it would have made it stiff and liable to sink...

Post by **Peter.N.** » 10 Apr 2011, 18:28

One of my XMs does that and its due to a worn height control valve.

Peter

Post by **CitroJim** » 10 Apr 2011, 18:32

Peter.N. wrote:One of my XMs does that and its due to a worn height control valve.

Is it a later XM with antisink Peter? With antisink a worn height corrector cannot cause sinking as the antisink valve totally isolates it... Antisink valves rarely give a problem...

lancia58 · Post by **lancia58** » 10 Apr 2011, 18:37

Rear corners means rear spheres ? I replaced them at the same time I replaced the rear anti sinking sphere two weeks ago. Where is the height control valve located ?

Thanks
Zohar

Post by **Peter.N.** » 10 Apr 2011, 18:40

No, I've never had one with anti sink, pardon my ignorance

Post by **CitroJim** » 10 Apr 2011, 19:05

lancia58 wrote:Rear corners means rear spheres ?

Yes, sorry Zohar. So used to Hydractive cars where 'corner' is used to differentiate the rear suspension cylinder spheres from the hydractive centre sphere... Should have been clearer..

Did the car sink before swapping spheres and can you feel any difference in ride comfort since changing them? Duff new spheres are not unknown.

The height corrector (control) valve is located in the middle of the rear suspension and can be recognised by a round black rubber cap on the end of it...

If the rear goes up and down normally and from and earlier thread you confirmed it did, then this item will not be at fault. As said earlier, it is isolated by the anti-sink valve and when the anti-sink valve is closed, the only culprits for sinking are the spheres or excessive leakage in the rear suspension cylinders.

lancia58 · Post by **lancia58** » 10 Apr 2011, 19:17

Yes the car did sink before swapping spheres and I can’t feel any difference in ride comfort. Regarding excessive leakage in the rear suspension cylinders when I check the LMH level it is OK. I know that there is a minor leakage in the pressure regulator but I guess it is not related. Each month I guess I top up not more than 50 cc of Total LMH.

All the three rear spheres are new . If one rear sphere is failed how will it effect the other sphere ? If there are not ticking from the accumulator does it mean that it is OK, last time I replaced it, it ticks a lot

Zohar

Post by **CitroJim** » 10 Apr 2011, 19:45

Zohar, before we continue, what is the exact model and age of your Xantia as if it is a Hydractive model or an early (1993) 'Sinker' then there are significant differences to consider. If it was an Activa then a degree of sinking both front and rear is normal due to the influence of the Activa system.

When I speak of leakage in the rear cylinders I don't mean leaks you can see but rather leakage internally within the cylinder that are invisible but causes excess LHM to return to the reservoir via the leakage return piping.

Fundamentally, on a standard non-Hydractive Xantia rear softness (or lack of) is controlled entirely by the rear spheres and after replacing the spheres and not curing it, the only possible causes are faulty (or wrong) spheres or mechanical stiffness in the suspension caused by faulty rear arm bearings or binding rear brakes. Wrong spheres such as Hydractive corners on a non-Hydractive car will result in a very stiff rear but will not cause sinking.

Bizarrely, stiffness in the rear bearings or binding brakes can cause sinking. Binding brakes are easy to check and if the rear arm bearing are bad the rear will rise and fall in steps possibly, accompanied by lots of creaking and groaning with visible negative camber when you look at the wheels from a distance.

Excessive leakage in the rear cylinders can be checked by pushing hard down on the rear to cause the height corrector to operate; if this causes an almost immediate tick from the regulator this can be a sign of high internal leakage as much more pressure than normal is called for to lift the rear back up.

On a car with generally good hydraulics a reasonably long interval between regulator ticks is a very good sign. Several minutes is possible.

lancia58 · Post by **lancia58** » 10 Apr 2011, 20:02

It is a none Hydractive 2.0 L 16v SX year make 2000. Indeed from time to time I do hear creaking from the rear suspension. I can recall that there were times when after I parked I heard some ticking from the rear suspension and I could identify that the source was the right rear suspension

Thanks
Zohar

lancia58 · Post by **lancia58** » 15 Apr 2011, 19:21

Hi Jim

Is there a way to verify if there is a leakage in the rear cylinders ? Without taking it apart ? I think it is the most reasonable cause to failure.If only one is leaking will it affect the other one ?

Thanks
Zohar

AndersDK · Post by **AndersDK** » 15 Apr 2011, 20:53

lancia58 wrote:Hi Jim

Is there a way to verify if there is a leakage in the rear cylinders ? Without taking it apart ? I think it is the most reasonable cause to failure.If only one is leaking will it affect the other one ?

Thanks
Zohar

On the rear cylinders you will find 2 plastic lines from the rubber bellow.
The rearmost (towards rear of car) of these plastic lines are the seepage/lubing leakback collector line, leading the cylinder leak-offs back to the LHM reservoir.
This leak is necessary to keep the cylinder piston rustfree and the piston & its seal lubricated.
You should understand that these lines are NOT pressurised, but they do get filled up and will carry quite an amount of LHM.

Lift the rear of the car remove the rearwheel in question, then lever down the car such the suspension arm STILL carries the weight of the car.
Using blocks or a support jack.

Prepare the area under the rear cylinder with papers, rags etc to collect any spillage.
Unplug the plastic line, immediately leading it into a jar.
A drillbit some 3,5mm will do fine as an endplug for the line.

The interesting part is how much leakage will come out of the rubber bellow stud from the cylinder, while the car is in normal height and weight on the wheel.

A single drop now and then every 20-30 seconds or slower (longer time interval), are no real concern.
The problem is evident if there is a fast dripling or even a constant flow.
Then the cylinder is leaking badly.

Btw : the frontmost plastic line is a simple bellow breather.
This line ends up inside the rear subframe to keep down dust ingress.

Btw 2 : despite the common assumption that the rear antisink sphere is only there as a rear brakes safety pressure reservoir, this sphere does impact rear sink, when it runs flat.
The hydraulic pressure function theory is complicated, but several instances of mysterious rearsink cases has been solved downright by replacing this sphere.