Xantia S1 Hard Rear Suspension - it's not what you think...

[Rhothgar]

Well today I confirmed that the leak to the strut top mounts temporarily, at least, to get it through an MOT is resolved with PTFE tape...

So whilst up at my mate's I thought I would regas the rear centre sphere.

Took the bung out. NO PRESSURE whatsoever. Not even the faintest PSSST!

Screw the new Valprex valve in and proceeded to charge it up. Put 35 bar in it as I couldn't find the actual spec in the Mechanics Handbook for a 1994 S1.

It soon dropped down to 10 bar so I thought that the diaphragm has split. Put a bit more pressure in and finally got it at a stable reading and left it for 10-15 minutes.

Came back to it and the pressure had held. GREAT!

Whilst the car was up in the air, I checked the rear spheres and the front spheres. I had put 52 bar in the fronts so decided to increase that to 60 as 1995 Handbook states 55+5-20 bar.

The front is absolutely beautiful now just driving it from the ramp to park it up. However, something didn't feel right and the rear end is now rock solid!!

NOW! The usual reason for this is that the spheres are severely depleted so what has gone wrong? What could the issue?

I have no idea if a 1994 S1 1.9TD has a one-way valve in the rear line but I am left wondering if the diaphram on the rear centre sphere is shot and I have ended up gassing up the rear circuit with 40 bar pressure and that is maybe preventing a one-way from opening and allowing fluid to the rear spheres?

It's very odd indeed.

Does anyone have any ideas please?

[RichardW]

On non hydractive versions the centre sphere is nothing to do with the suspension. If the ride height is correct you have either blown a sphere, or an arm bearing is seized.

[Rhothgar]

On non hydractive versions the centre sphere is nothing to do with the suspension. If the ride height is correct you have either blown a sphere, or an arm bearing is seized.

Does it not link in any way via the supply piping then, Richard?

The spheres are all holding pressure and the trailing arms are not seized. It's all articulating as it should. UP! DOWN! UP DOWN!

I am mystified as to what it could be. I think I will remove the caps and check to see if any LHM is coming out of the corner spheres. Of course, there shouldn't be any.

Knowing my recent form of bad luck, they probably will need replacing given I have bought the gassing rig...

[xantia_v6]

I don't know what sort of lift you had the car on, but when regassing spheres on the car, the relevant hydraulic circuit must be completely depressurised.

The third sphere at the rear of a non-hydractive Xantia is a brake accumulator for the rear brakes and has no effect on the suspension.

[Rhothgar]

It was a 2 post.

System was fully depressurised prior to regassing hence why I thought the diaphragm am was split but then it holds fluid?

[CitroJim]

Is the height corrector working as it should?

[xantia_v6]

It was a 2 post.

System was fully depressurised prior to regassing hence why I thought the diaphragm am was split but then it holds fluid?

On a system with anti-sink, depressurising at he main regulator does not release the pressure in the suspension (front or rear), due to the anti-sink valves. You need to lower the suspension with the release bolt closed and engine running for 30 seconds (to keep the anti-sink valves open) before opening the release bolt.

[Rhothgar]

Is the height corrector working as it should?

Of that I am not sure Jim.

The front looks too high to me. I do need to do a full fluid change as I put some contaminated fluid in the other week that looked as though it had been opened for 15 years because I ran out and that’s all that was at my mate’s.

When MOT chap said to me to run it up and down the road, I noticed that the back was low. I may have taken a video. I cannot recall. The back did struggle to come up yesterday so I nudged into into high for a few seconds to get it moving.

I have already stripped a spare height corrector down and left it soaking in paraffin at another mate’s. I left the seal in the paraffin too and then had a thought this week that that was probably not a good idea!!!

[Rhothgar]

I don't know what sort of lift you had the car on, but when regassing spheres on the car, the relevant hydraulic circuit must be completely depressurised.

The third sphere at the rear of a non-hydractive Xantia is a brake accumulator for the rear brakes and has no effect on the suspension.

Do you know what? I cannot actually remember what I did this time. I usually do. I definitely put it on low but whether I had left the engine running U cannot recall.

I recall putting the ranp up and deciding to lower it again and up again and lower it again.

I have a feeling I did this because I wasn’t happy with something?

How would this cause the issue I now seem to have? ie if I had not left it running.

I was also distracted by the fact that although the engine had been idling for over half an hour when I came to restart it (probably to depressurise?) it literally started and died immediately. I must have tried 15 times to start it and it just died every time as just as it had started. In the end m, I held the key in the start position after the engine had started and it then kept running.

Looks like I’ll have another problem to resolve soon enough.

[Stickyfinger]

Start at the beginning again.

On high, lube the correctors, check the dog bones etc....then..

As was said above, get the car down and running to depressurise correctly.
Pull off the corner spheres and check pressures.
Whilst it is down check the movement in the height corrector.
Then restart and check full body up/down movement/bubbles disappear from the LHM tank (ensure you bleed the steering by moving it 4/5 times --do not hold it at the extreme)---
Check road height after some forward/back movement.

[thorter]

My recollection of depressurising the rear suspension of an anti-sink Xantia is that it can be quite confusing. This is because the anti-sink valve remains closed until such time as the main hydraulic pressure exceeds the pressure in the anti-sink sphere, which may have “peak charged". So it can take a while with the engine running and the suspension lever at low before the rear pressure is released. Further, with the rear wheels hanging, it is even more difficult to understand what is happening.

[Rhothgar]

Well I am a little bit more confused now.

For the avoidance of doubt, this is on my S1 1994 1.9TD.

The official handbook states none of this. Leaving the engine running appears to be only relevant for cars with SC/MAC and SC/CAR and which it doesn't seem to define what either are but it is clear that SC/CAR appears on the cars with active suspension ie Activas.

So all the manual says is put on LOW and undo the screw. It makes no mention about keeping the engine running to depressurise anti-sink valves? Then again, as an official Citroen handbook, it even fails to give a pressure rating for the rear centre sphere which is no. 3. It only refers to Sphere 3 on hydractive so clearly you cannot even rely on Citroen's own documentation. If it was Haynes then you'd expect it to be wrong...

Let's say this is the procedure I followed (other than the heightening and lowering of the ramp to bring the car onto its wheels - for whatever reason I did that...).

I did fail to actually repressure it according to the manual. Normally I just nip the bleed screw up which is what I did. That would probably explain why even after 1 minute the suspension had failed to move!

And I forgot to mention also that the fluid is now ABOVE the highest mark when the suspension is on high because the rear centre sphere had NO gas in it so regassing it and pushed 400cc of fluid back into the system because I had correctly filled it on high beforehand. There's a lesson!

As far as I recall, the car only has 6 spheres. 2 front, 1 accumulator, 2 rear and one anti-sink denoted by 2, 1, 3 and 5 respectively in the following snip:-

[thorter]

I managed to find Citroen diagrams for anti-sink operation. You can see it is a bag of tricks. It is prudent that there is weight on rear wheels to be sure the suspension is fully depressurised.

Here is a bit more explanation. To reduce pressure regulator cycling, the cut in pressure (thus main accumulator pressure) is quite a lot less than the cut out pressure. If the rear suspension was put on high in the course of working, the pressure in it can reach the maximum cut out value. Then if the main pressure falls, the anti-sink valve operates to isolates the rear suspension from the height corrector. I found sometimes it could take several minutes before the main accumulator pressure was again enough to release the anti-sink valve. Indeed, it is not very clear why the anti-sink valve will necessarily open when the two pressures are exactly equal.

I would also suggest that it is best to remove the sphere before re-pressurising. As hydraulic fluid is more or less incompressible, consider the case when the rear suspension has become isolated, and say the residual gas in the sphere to be filled is compressed down to 100ml. This is released, then refilled to 50 bar, but this in fact will become 12.5 bar actual fill pressure at the full 400ml.

[Rhothgar]

That's really helpful seeing those diagrams Thorter.

Thanks for digging the information out.

So I take it that 8 and 9 are the anti-sink valves which according to the next page are actually SC/MAC despite that also saying that it is for hydractive cars only.

I think I have been confused about this before now. I always thought hydractive were the cars with the 8 mm pipes. I think on the later cars that might be the case but my S2 also has 3.5mm pipes. I know I have seen the aluminium blocks on one of the cars but cannot recall which one. They may even be on both.

I can now see that the SC/MAC valves can appear on both hydractive and non-hydractive versions.

What is item 4 then at the front please? That looks as though it might have an electrical connector attached to it.

Could I have the description of the non-hydractive SC/MAC valves which I assume is Page 7 please?

[thorter]

Yes, SC/MAC is just the anti-sink system. Here are rhe other relevant pages, including hydroactive for comparison.