Sinking xantia

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Bobcat
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Sinking xantia

Post by Bobcat »

Hi All although i am a Nissan master tech , i have recently taken ownership of 2x xantias one was my father in laws 1996 1.9td with 250116 on the clock runs like a dream, the other was a trade in at work & is a 1998 1.8 16v with 134000 on the clock this one has a problem i think when left standing over night it sinks to the lower suspension setting but when started rises reasonably quickly and remains there the ride is smooth and the brakes work fine.
Any help appreciated Tim :?
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Post by AndersDK »

Hi Bob -

Welcome on board and grats with 2 comfy cars ... :wink:

I'm pretty sure the rearsink on the 1.8 is caused by a nearly flat rear anti sink sphere.
Its located somewhere under rear of the car, recognised by its single small 3.5mm outer dia pipe connecting to the center of the sphere base.

That is - if this Xantia is equipped with Anti-sink (mostly they are).

You will need either a pit or ramps working under the car, as it must be depressurised in low setting on the height selector knob, while engine is running.
Once its low you can stop engine.

You will need to remove the pipe from the sphere as the first task, before trying to remove the sphere. Otherwise you will most certainly shear the pipe.
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Post by Xaccers »

Hi Bob, with the engine running, can you hear any ticking from the front of the car?
If it ticks more than once every 30 seconds then you have a flat accumulator sphere.
Like the rear sphere we call the anti-sink sphere, it stores pressure in the system. The accumulator holds enough pressure when new for about 50 uses of the brakes.
When it's pressure gets low, the regulator works harder, hence the more rapid ticking.

The age of your cars means they'll have an anti-sink sphere at the back. If they're LX or SX models then they'll have 6 spheres (one for each corner and the two accumulators).
The corner ones are for the suspension, and normally they're the only ones that get changed because it's obvious when they're flat.
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Post by bruno »

Please someone correct me if I'm wrong but shouldn't the brake doseur valve close up the rear hidraulic circuit when the anti-sink sphere is flat? If so, the rear shouldn't drop until the next morning when you turn the car on and the system pressurizes again...
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Post by AndersDK »

bruno wrote:Please someone correct me if I'm wrong but shouldn't the brake doseur valve close up the rear hidraulic circuit when the anti-sink sphere is flat? If so, the rear shouldn't drop until the next morning when you turn the car on and the system pressurizes again...
Yes -

It SHOULD - but does not always do so ...
Thats basically why the antiisnk system was incorporated in the first place ... :wink:
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Post by Xaccers »

With regards to the doser valve, how would you test it and how difficult (and costly) is it to replace?
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Post by FrenchLeave »

Bobcat wrote that the car rose reasonably quickly when the engine was started. This suggests that his car has the older 5 piston pump with its full output available to lift the suspension - and in that case the car won't have anti-sink and its behaviour is as expected. The overnight sinking is caused by pressure from the suspension leaking through the height corrector and the brake control (doseur) valve.

Presence of the older pump is easily checked by lifting the bonnet and seeing if the pump has one or two high pressure pipes coming from it, the older pump has only one.

When Citroen introduced the later 2+6 piston pump its output was split with only the 2 piston part supplying the suspension (and rear brakes) whilst the 6 piston part supplied the steering. This did away with the need for a priority valve, but pumping the suspension up took forever. Hence the need to isolate the suspension from the leaky height control and brake valves and this is the sole reason for fitting the anti-sink valve.

This in turn created another problem. If the car suffered hydraulic failure whilst driving, the rear anti-sink valve closing caused the rear brakes to be cut off from the rear suspension, so they lost their supply of pressure fluid. The answer that Citroen came up with was to fit an additional store of pressure fluid (another accumulator sphere) that would be available for the rear brakes when the A/S valve closed. Because this sphere was needed as a result of fitting the antisink valve they called it the antisink sphere, it would have been better to call it the rear brake sphere - it would have saved a lot of confusion.

So if, when Bobcat checks his pump, he finds it has two pressure pipes then he has antisink and an antisink sphere; but a flat sphere cannot cause the car to sink because it's isolated from the rear suspension by the A/S valve, as are the HC and brake control valves. A flat antisink sphere does mean there is no supply to the rear brakes if you suffer hydraulic failure.

There are I believe only three items that can cause sinking on a car fitted with antisink: The A/S valve itself, but it's a simple mechanical pressure valve and failure is almost unknown; the hydractive control valve; leakage past the piston on the suspension cylinders (I know of three cases, one being my own V6).

Any internal leakage is returned to the reservoir, so check the return lines with the engine running to identify the leaky component.

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Post by DickieG »

Just to clarify a few issues here where some threads have inadvertently gone off track, the relevant car is a 1998 Xantia 1.8 16V which will definitely have been fitted with a 6 + 2 pump complete with anti-sink, but not with Hydractive suspension.
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Post by AndersDK »

Xac wrote:With regards to the doser valve, how would you test it and how difficult (and costly) is it to replace?
Check the leak off from the valves 2 return lines while the brake pedal is not touched and engine idle.
The leak off should ideally be nil, but really bad valves may show a constant leak off flow - i.e. not just dripping.

If you remember that the rear suspension circuit feeds the doseur valve rear brakes circuit, you also know why a leaking doseur valve will cause rerar sink.

That said - its more often the main feed (i.e. front brakes) that leaks from the doseur valve - and then the rear suspension cylinders themselves that leaks and causes the rear sink.
Then you should check the leak off flow from the rearmost plastic pipe in the rear cylinder bellows- each side - to conclude where the leak is.

PS : have no idea how bad it is to replace on a RHD, but it certainly aint easy ... :roll:
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Post by CitroJim »

AndersDK wrote: PS : have no idea how bad it is to replace on a RHD, but it certainly aint easy ... :roll:
Some are OK and some are very difficult due to poor access and the presence of an aircon pipe.

The easier ones are the 8V petrols, the non-turbo diesels and remarkably, the V6!

The difficult ones are the Activa, and the TDs. I reckon the 16V models, with their wide heads will be somewhere between the TDs and 8V petrol models in terms of access (i.e. not that easy).

The basic test is can you easily see the dosuer? If not then it'll be tricky.

Luckily, the leakage return pipe from the dosuer is readily accessible in all models and can be identified as a thin pipe that runs from the LHM reservoir across the bulkhead to the dosuer. It can easily be disconnected at the reservoir end to conduct the Anders's test.
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sinking xantia

Post by Bobcat »

:? :? :? :? Well Friends im con fused where is and what is a doser valve what does it do what does it look like? as for difficulty i have a full nissan w/shop at my disposal as i am in charge so please explain as to my next move if i find the return s leaking.
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Re: sinking xantia

Post by AndersDK »

Bobcat wrote::? :? :? :? Well Friends im con fused where is and what is a doser valve what does it do what does it look like? as for difficulty i have a full nissan w/shop at my disposal as i am in charge so please explain as to my next move if i find the return s leaking.
Bob
Sorry about that Bob -

My first check would be the leak off pipes on the rear cylinders bellows.
Its the rearmost (towards rear of car) plastic pipe that carry the cylinder leak off.
The frontmost pipe is simply an air vent pipe for the bellow.

The plastic hose unplugs the bellow and then you can insert a length of suitable dia PVC hose, as when you do a brakes bleeding job.
Note that the unplugged hose may leak considerable amount of LHM (from the opposite side). Better lead it into some sort of a container.

Observe during 10 mimutes the leak flow while engine idle and car in normal height, AND the wheel (or suspension arm) under load.

A flow will evidently make the rear sink fast.
But even a slow dripping will also cause rear sink - after longish time.
The cure is to replace the rear cylinder seals - or the cylinder.

However ; if you dont find any significant leak off from the cylinders, then the doseur valve is the suspect candidate.
(The doseur valve takes place of the master brake cylinder on ordinary cars).
Its located clamped between engine block and drivers footwell, just behind the pedal box.

As Jim explains the return hose is rather simple to access at the reservoir.
Testing is as described earlier.
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Post by lexi »

So to simplify : are the thin hoses on reservoir simply returns from faulty seals (Doseur and suspension) that should not have any fluid coming through them? Pull off hose and watch it?
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Post by Old-Guy »

Bobcat

Welcome to the forum.

As an expert vehicle technician, you'll have to get your head around the fact that a 'hydraulic' Citroen isn't like the 'conventional' cars that you're used to. On Xantias, the hydraulic system powers brakes, steering and suspension. Only Liquide Hydraulique Minerale LHM), which translates as mineral(-based) hydraulic fluid, must be used. All other brake and hydraulic fluids are incompatible and will wreck the entire system making the car a write-off.

The Doseur valve is what the brake pedal operates - it allows high pressure LHM into the braking system and provides 'feel' by being designed so that the force required to open the valve is proportional to the pressure in the braking system.

The PAS is the one fairly conventional part of the hydraulics. The basic Xantia hydraulics seem complex, until you consider that there's no brake servo (or vacuum pump on a diesel) and the suspension spheres (£20 each) take the place of springs and self-levelling dampers.

BTW, the powered brakes makes bleeding brakes on a Xantia an absolute doddle, don't be mean with the LHM (unlike the rest of the hydraulic system, the lines to the calipers are dead-ends that get full of dirty old LHM that got very hot. To avoid cross-contamination, a separate bleeding 'kit' is essential - a length of suitable polythene pipe and 1L mineral water bottle or similar.

IMHO a Xantia, with suspension and brakes in good condition, rides
and stops like nothing else.
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Post by vince »

Hi Bobcat, are you by chance the same Bobcat off Edition 38 forum?
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