Anti sink not working

Stempy · Post by **Stempy** » 19 Feb 2006, 21:05

I have a little problem that maybe someone can advise me on. The rear anti sink system on my Xantia does not seem to be working properly. When left over night the rear will sink right down like on early Xantias and when braking the rear end rises up. I changed the anti sink sphere a while back, not for this problem, just as routine, but this problem has started happening recently. Is there a way to test the sphere or could it be the anti sink valve?

jeremy · Post by **jeremy** » 19 Feb 2006, 21:12

I expect Simon (Mandrake) will be along later and he will probably need some more details of your car - like age and model spec.

The anti-sink sphere probably won't cause the car to drop when it stands as its purpose is to provide a supply of high pressure LHM to prevent problems when the anti-sink valve opens.

Mandrake · Post by **Mandrake** » 20 Feb 2006, 01:14

Stempy wrote:I have a little problem that maybe someone can advise me on. The rear anti sink system on my Xantia does not seem to be working properly. When left over night the rear will sink right down like on early Xantias and when braking the rear end rises up. I changed the anti sink sphere a while back, not for this problem, just as routine, but this problem has started happening recently. Is there a way to test the sphere or could it be the anti sink valve?

Sounds like two seperate problems there, so first the easy one -

The rear rising up excessively when braking simply means that the rear brakes are not working as well as they should, as it relies on the torque from the rear brakes to counteract the torque from the front brakes to prevent the rear lifting.

When the front brakes bite the torque from the braking effect tries to pivot the entire car forward on the front wheel axis, thus lifting up the back, however the bite from the rear brakes tries to rotate the trailing arms in the direction of the wheel travel which applies a counteracting force which pushes the rear suspension down.

They seldom equal each other exactly so there will always be a little bit of up or down movement at the back under hard braking, but it shouldn't be excessive.

I'd bleed the rear brakes thoroughly, check the surfaces of the pads and discs to see if they're good, and also try pushing back the pistons to make sure they're not seized.

On to the anti-sink problem - my initial reaction is "not sure".

I'd need a bit more info on how quickly it goes down, also what is the condition of the accumulator sphere ?

As a test that may provide some useful data, try opening the bonnet, run the engine until the height stabalizes at the normal height, turn off the engine, immediately open the pressure regulator bleed screw half a turn to bleed the pressure, this should force the anti-sink valves to close immediately.

Now try setting the height lever right down - if the rear goes down the rear anti-sink valve must be sticking open. (Unlikely IMO)

Assuming that it doesn't go down (and thus the anti-sink valve is probably ok) close the regulator bleed screw again, set the height lever back to normal, run the engine to let the height stabalize at normal height, switch off the engine, open the bleed screw to bleed the pressure and then close it again, but this time let the car sit and see how long it takes to go down.

The point of this test is that it will force the anti-sink valves to close immediately, which should in theory eliminate any interactions between the anti-sink sphere pressure and the accumulator pressure.

Let us know how long it takes to go down in this condition...if it goes down in minutes it could have internal leakage in one of the rear suspension cylinders.

Regards,
Simon

Stempy · Post by **Stempy** » 20 Feb 2006, 07:30

Thanks, what I have also noticed is that when I switch off the ignition, and this can be engine running or not, there is often a ratcheting sound that comes from the rear that lasts about a second.

The suspension rises and falls with the lever as normal. When I stop the engine I can watch the back end sink slightly then come to a stop where you might expect under normal conditions. It takes a few hours of standing for it to sink right down, but it rises up again quickly with no problem. Accumulator sphere is only a few weeks old so should be ok.

The car has HA2, I have done a test whereby I removed the fuse that supplies the suspension ECU pumped up and down then replaced the fuse, and it jumps up as the electrovalves open so I think the centre comfort spheres and valves are ok.

Another thing is that when braking as I come to a stop the brakes seem to release slightly for an instant and then re-bite. As I'm writing this I'm thinking more and more that it could be air in the system, but like you say it could be multiple problems knowing what Citroens are like. I did overhaul the rear brakes last year so I'm hoping that they are still ok.

Mandrake · Post by **Mandrake** » 20 Feb 2006, 08:39

Stempy wrote:Thanks, what I have also noticed is that when I switch off the ignition, and this can be engine running or not, there is often a ratcheting sound that comes from the rear that lasts about a second.

Hmmm, a ratcheting sound from the rear ?

Does the height move during this strange sound ?

When you switch the ignition off, the Hydractive electrovalves switch off for a fraction of a second and switch back on again for 30 seconds. If there is a height change when this happens, it suggests that the electrovalve was not open to begin with.

A problem that I have with my car is intermitant bypass leakage in the front electrovalve, which occasionally causes either the front OR the rear to stick in the hard mode when it should be in soft, and then during the next hard->soft mode transition it will actually switch to soft.

Another symptom of this is a very quick regulator cycle time with the hydractive fuse connected (12 - 18 seconds in my case) but a normal regulator cycle time with the fuse removed.

The suspension rises and falls with the lever as normal. When I stop the engine I can watch the back end sink slightly then come to a stop where you might expect under normal conditions.

Is that sinking in response to a load change, eg you getting out of the car just after turning the engine off, or is it happening in response to the engine stopping ? EG if you are standing outside the car and you turn the engine off via the window without causing a load change, does it still sink before your eyes just after turning off the engine ?

If so you DEFINATELY have a fault, and it might be a leaky HA2 electrovalve.

They can leak (internally) in the ON mode if the needle valve seat doesn't seal properly - as mine is doing, and they can also leak in the OFF mode if the small green o-ring on the electrovalve shaft is leaking.

Apparently on early models without anti-sink if this o-ring leaks the suspension can go right down in just a few minutes after turning off the engine, but the same fault in a later model will be largely masked by the anti-sink system, and not so noticable.

It takes a few hours of standing for it to sink right down, but it rises up again quickly with no problem. Accumulator sphere is only a few weeks old so should be ok.

Ok, if you think the accumulator sphere is good, try timing the regulator cycle time both under normal conditions, and again with the HA2 computer fuse removed. If there is a large descrepancy you may have a similar problem to mine, but perhaps worse.

The car has HA2, I have done a test whereby I removed the fuse that supplies the suspension ECU pumped up and down then replaced the fuse, and it jumps up as the electrovalves open so I think the centre comfort spheres and valves are ok.

I'm not sure that thats a particularly meaningful test, a better test would be to perform a normal bounce test at both ends with the fuse removed and the fuse fitted (engine running in both cases) and compare the springing stiffness.

There should be a VERY obvious difference in the suspension stiffness between the two modes.

Another thing is that when braking as I come to a stop the brakes seem to release slightly for an instant and then re-bite. As I'm writing this I'm thinking more and more that it could be air in the system, but like you say it could be multiple problems knowing what Citroens are like. I did overhaul the rear brakes last year so I'm hoping that they are still ok.

They should be mechanically ok, but air may have got into the lines.

You say you replaced the anti-sink sphere, but did you bleed the rear brakes after that ? Replacing any of the rear spheres will introduce some air into the rear suspension and if you're unlucky some may find its way into the rear brake circuit, so to be safe always bleed the rear brakes after removing any rear sphere.

Also, I didnt realise your car was HA2 - in which case it definately shouldn't be lifting significantly at the back during braking as the HA2 system automatically switches the suspension to hard mode during any moderate to hard braking which severely limits any tendency for the rear suspension to lift.

If you get a chance, try to perform the tests I suggested in my first reply involving the regulator bleed screw as well.

Regards,
Simon

Stempy · Post by **Stempy** » 20 Feb 2006, 11:47

Thanks again. I'll bleed the brakes first then try the various tests and see what happens. Probably won't be until the weekend though.

I did try the bounce test. With the fuse in place the rear is very bouncy as you would expect, then removing the fuse makes it much stiffer for a while, but then it goes back to bouncy again all on its own which I dont think is quite right.

The front seems quite stiff whatever, but it is due for a pair of corner spheres, only the centre one has been replaced, but I'd like to get the rear sorted first.

AndersDK · Post by **AndersDK** » 20 Feb 2006, 23:45

Its known that the electrovalve may suddenly start leaking - because of a bad O-ring seal.
Defo with Simon here : first go is to ensure the system is vented and brakes are bled properly.

I dont recall we have had a HA2 discussion with a symptom like a ratcheting sound. This clearly must be the electrovalve trying to tell something ...

It could in fact be a bad (intermittent) coil in the electrovalve - Simon ?

Mandrake · Post by **Mandrake** » 24 Feb 2006, 09:36

AndersDK wrote:I dont recall we have had a HA2 discussion with a symptom like a ratcheting sound. This clearly must be the electrovalve trying to tell something ...

It could in fact be a bad (intermittent) coil in the electrovalve - Simon ?

I don't know unfortunately, as I havn't had it happen or heard of it happening, but I suppose it is possible.

One slight posibilitiy that could make that noise is if the back EMF clamping diode built into the electrovalve went open circuit. This happened to bernie's car so perhaps he can comment on whether the electrovalves made a chattering noise when the diodes were faulty ??

(It certainly stopped them from working properly, if nothing else)

Regards,
Simon

bernie · Post by **bernie** » 24 Feb 2006, 11:23

Mandrake wrote:
AndersDK wrote:I dont recall we have had a HA2 discussion with a symptom like a ratcheting sound. This clearly must be the electrovalve trying to tell something ...

It could in fact be a bad (intermittent) coil in the electrovalve - Simon ?
I don't know unfortunately, as I havn't had it happen or heard of it happening, but I suppose it is possible.

One slight posibilitiy that could make that noise is if the back EMF clamping diode built into the electrovalve went open circuit. This happened to bernie's car so perhaps he can comment on whether the electrovalves made a chattering noise when the diodes were faulty ??

(It certainly stopped them from working properly, if nothing else)

Regards,
Simon

Yes, it did make a ratchet sound before I fitted new diodes.
It was the valves oscillating.

Stempy · Post by **Stempy** » 24 Feb 2006, 15:20

What type of Diode did you use Bernie? I suspected there may be something wrong with the rear valve as it seems to have a mind of its own as to whether it would be hard or soft.

bernie · Post by **bernie** » 24 Feb 2006, 15:44

Stempy wrote:What type of Diode did you use Bernie? I suspected there may be something wrong with the rear valve as it seems to have a mind of its own as to whether it would be hard or soft.

I used 1N1004 but I've been advised that 1N4004 is a better bet.

My 1N1004 diodes are still working but I'm leaning towards my HA2 valves playing up (ala Simon)

Stempy · Post by **Stempy** » 24 Feb 2006, 17:51

Thanks Bernie, looks like I might also be in for a complete rear end strip down then

bernie · Post by **bernie** » 24 Feb 2006, 18:19

Stempy wrote:Thanks Bernie, looks like I might also be in for a complete rear end strip down then

Try the diode first, you never know

Stempy · Post by **Stempy** » 24 Feb 2006, 18:42

I'll do that, but just one more thing, which way round does it go?

AndersDK · Post by **AndersDK** » 24 Feb 2006, 18:46

Stempy wrote:I'll do that, but just one more thing, which way round does it go?

One of the coil wires would be at (or nearly at) chassis potiential. Test out with a VOM. This is where the Anode of the Diode should connect. I.e. it should be reverse connected not to shortcircuit the RF pulsing.

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Anti sink not working

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