Xantia TD Hydraulics

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paul2309
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Xantia TD Hydraulics

Post by paul2309 »

Hi All
Thanks to this site I've solved quite a few probs, but am a bit stuck on this one.
I'm about to change all 4 spheres on my Xantia TD, even though they appear OK doing a bounce test, as the ride has become very hard and rattly.
However, sometimes when I'm sat with my foot on the brakes, at traffic lights for instance, the back end will suddenly drop, then rise again when I take my foot off the brake to pull away.
It has also started to drop at the back end with a whistling sound when I stop the engine, but does not drop when the car is fully loaded with all my disco gear in it.
So, do I also need to replace the rear accumulator sphere, or is it more likely to be the anti sink valve.
Any help much appreciated before I spend more money than I need to.
Paul
peter1138
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Post by peter1138 »

Are you holding the brake pedal constantly after slowing? If so then it will hold the back end of the car up, the suspension will adjust for this, and then when you release to pull away it will rise again. (At least, in my experience)
Try using the handbrake :-)
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Kowalski
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Post by Kowalski »

Before you go replacing spheres, check whether the suspension height is correct. If it is correct and the ride is hard it needs new spheres. The suspension on a Xantia can get stuck too high or too low, its usually obvious if this has happened.
The sinking when you hold the car on the brakes is normal for a Xantia, the reason why is complicated but I'll try to explain why.
The wheelbase of a Xantia varies with suspension height (it gets shorter when the rear suspension goes up) and when you brake it makes the rear suspension go up. When you stop and hold the car on the brakes, you are using the brakes to keep the wheelbase "short" and keep the rear suspension high, the height corrector will try to compensate for this and get the suspension height back to the right height. As the height corrector releases rear suspension pressure, it expects the rear of the car to fall, but it cant fall because the brakes are holding it. One of two things will then happen, either the brake pressure won't be enough to hold the suspension height i.e. far too much rear suspension pressure is lost and the brakes can't hold up all of the weight of the car so it falls. Or you take your foot off the brake and the suspension falls again because it has lost too much pressure. In either case this is normal behavior for a Xantia, the solution is to not hold the car on the foot brake, and use the handbrake instead (you'd fail your driving test if you did't use the handbrake).
I'm not sure about the car sinking when you stop the engine, this could be a problem with an anti sink valve, brake valve or a height corrector rather than being a straight forwards accumulator sphere problem. Sometimes when you've got this sort of valve problem it can be remedied by having the LHM system flushed (replace LHM with Hydraflush or equivilent, drive 1500miles replace with new LHM).
paul2309
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Post by paul2309 »

Cheers folks
The dropping on brakes sounds right to me, excellent explanation, so I think I'll just have a look at the anti sink valve.
The suspension height is correct and moves freely from low to high with the lever inside the car so I think I'll risk the money on replacement spheres.
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Post by paranoid »

Kowalski......I have tried to put that into words since I got a Citroen Well done!!!!!!!
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Post by oilyspanner »

That sounds exactly like a diagnostic test for BX rear brakes being OK,
Stewart
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Kowalski
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Post by Kowalski »

It'll tell you that one of your rear brakes works and it'll maybe give you some idea of how well too.
If one rear brake didn't work at all and the other one worked well would you get the car leaning over at an angle because that side was held up at the rear and the other side wasn't?
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