Rear drop

silverback · Post by **silverback** » 06 Jun 2005, 02:12

Hi all. My '99 Xantia Hdi rear end drops when it is started up after it has been standing for a few hours. The car will 'stay up' all night, but when I start it in the mornings, the rear end will drop to the floor, then raise after a few seconds.
I have read that it may be the acumulator sphere, but I would be grateful for any advice.
The suspension on the whole seems a bit hard as well. My Renault Kangoo van rides over rough roads better than my Xantia, so something isn't right.
Any advice would be appreciated.
[:)]

Post by **martyhopkirk** » 06 Jun 2005, 02:58

Likely the rear accumilator (anti sink sphere) is a bit flat. Sounds like the right symptoms there. If they are original spheres tehn they are getting a bit past it age wise now.
Bite the bullet and get all 3 rear spheres replaced (or set aside a saturday afternoon to do it yourself) In fact if your feeling flush do all 6. Flat spheres do ride hard. Do a hydraflush too whilst your about it and give the system a good clean (use the search function to find a more detailed desscription of hydraflushing).
Good Luck

silverback · Post by **silverback** » 06 Jun 2005, 03:35

martyhopkirk, thanks for the prompt reply.
I have in fact changed the LHM about 3 months ago, but didnt Hydraflush.
The suspension is softish when I press the corners, but isn't what I would expect on the road.
I get a few 'rattles' as well from the front end over rough roads (drop links?) and a bit of a wobble when accelerating hard from rest.
Would just fitting new spheres and maybe droplinks cure the 'hardish' ride.
Regards
Pete

adamskibx · Post by **adamskibx** » 06 Jun 2005, 03:54

Hello
I would change as many spheres as you can giving priority to the anti sink sphere and rear spheres. Then bleed the hydraulics if the problem persists. The rattle you mention could be the droplinks-they may just need tightening but the wobble you mention is more likey to be something like ball joints or lower arm bushes worn out, I dont think a loose droplink could cause the wobble as such. There are a few components like this that could have worn out if the car has done much more than 100000 miles I suspect. The best way to test if its the suspention bushes or ball joint is to brake in a straight line, then reverse up to 5/10 MPH and apply the brakes- If you hear a clunk a fraction of a second after hitting the pedal it will be the suspention bushes-or ball joints- Check the ball joints by jacking the car up and trying to move the wheels etc to see if there is any play- Im no expert but from my few years of Citroen ownership, this is how I would approach it. Id take Martys advice and change the spheres before tackling the rattles etc.
Adam

JohnT · Post by **JohnT** » 06 Jun 2005, 04:18

Have I got things wrong? The anti sink sphere is there to stop the car sinking when the engine is inactive? When you start up the system then relies on the accummulator to maintain pressure to the system from the start up until the system re pressurises. If this is faulty the rear end will drop? Have I got this wrong?

adamskibx · Post by **adamskibx** » 06 Jun 2005, 04:24

I think this is what goes on JohnT- In this case perhaps the cars rear is sinking only once the driver gets in the car???, and it might be hard to notice, so you only notice it go up when the engine is started. If somethings sticking a bit it might well stay up all night then sink when someone gets in. Im not a Xantia owner so I only know about anti sink spheres from what ive read on here.

JohnT · Post by **JohnT** » 06 Jun 2005, 04:39

Ummmm. very interesting! What does seem to be a consideration here is that the pump will take the least form of resistance, in that it is easier to lift the back than the weight at the front? not sure what that means yet but will sleep on it!

JohnT · Post by **JohnT** » 06 Jun 2005, 04:44

Adam....back again....is the system responsive in the non engine running mode? Surely if the system recognised the extra load on start up it would rise to compensate for that weight? Going to kip! Good night.

adamskibx · Post by **adamskibx** » 06 Jun 2005, 05:13

From what I undertsand the anti sink valve and sphere only operates when the engine is off. Think there is a valve which remains closed until the pressure from the suspention struts reduces to a pressure below that of the accumulator supply due to slow leakage into the low pressure return circuit through the small tolerances in the struts and height correctors. When the valve opens it lets out pressure that should be built up in the anti sink sphere if its OK and this compensates for the amount of fluid between sphere and strut. Tecknically then, yes the car should raise as soon as the engine is started even if the anti sink has gone flat- Im just wondering if the car looks normal and then sinks when the driver gets in rather than when the engine is started- Im sure Silverback is eithernot noticing it sinking as he sits in it, or, he's dead right about whats happening, in which case, ive no idea-all id do is check LHM levels and bleed the system thouroughly.
Regards, Adam

silverback · Post by **silverback** » 06 Jun 2005, 12:03

Just to clarify, the car will sit straight and level all night. I can sit in it and it doesn't sink much. When I start the engine the rear end drops to the ground (minimum height/bumpstops), then after a few seconds, it will pump up to normal ride height.
It's only just started doing this and behaves normally the rest of the time apart from feeling a bit hard when driving.
I did press each corner and it feels soft. It's only when on the move it feels hard.
Incidently, passengers have commented 'what a lovely ride the car has', I just know it could be better, like my previous Xantia, or my mates C5.
Regards
pete

Stempy · Post by **Stempy** » 06 Jun 2005, 12:42

If the anti sink sphere is flat then you will find that the back will drop as you start the car. I know this as it happened to me. Technically I'm not 100% certain but I think what happens is the anti sink valve opens when pressurised by the pump and the lack of pressure in the sphere causes the sudden drop. This happens as rear hydraulic pressure is lost for an instant filling up a flat sphere, the height corrector will then compensate and the rear pumps up.

DoubleChevron · Post by **DoubleChevron** » 06 Jun 2005, 12:58

Hi Guys,
the only thing that will influance the back dropping to a great extend is the anti-sink valve (even it will leak slowly).
The 'anti sink' sphere really has nothing to do with the sinking ability of the car, it is infact a rear brake accumulator. If the Xantia is riding poorly and has a fast cycle time I strongly suggest you get all the spheres (including) the H/A spheres regassed ASAP.
seeya,
Shane L.

silverback · Post by **silverback** » 06 Jun 2005, 13:05

New spheres it is then!
Thanks guys.

Post by **RichardW** » 06 Jun 2005, 13:44

I think by parts you guys have got the story!
The anti-sink valves (one front, one rear) are what stop the car sinking. As mentioned when the system pressure drops below the suspension pressure they close, isolating the suspension, and making the only leak path the suspension struts (unless it's hydractive, in which case I think there are others associtated with the hydractive valves). The main function of the rear anti-sink valve is to act as a brake accumulator - since the rear brakes are fed off the rear suspension, when the anti-sink valve is closed, there is no pressure to the rear brakes. In the event of a system failure, the A/S valve would close, and the rear brakes would have no pressure. It may also provide some back pressure to keep the A/S valve closed, although I am not how and why. What happens when it is flat is that as the anti-sink valve opens, the pressure equalises in the rear suspension components - including the anti-sink sphere. If the pressure in the sphere is very low, when the anti-sink valve opens, all the LHM rushes into the sphere and the rear suspension collapses, then raises back to normal height.