Rear spheres for Mk2 Xantia

rmunns · Unread post by **rmunns** » 03 Aug 2010, 23:21

I've just ordered three rear spheres for my September 2000 Hdi90 Forte saloon.

Should they all be the same? If I have two of one pressure and one of another pressure then I guess it's obvious which goes where.

At present the suspension does not stay up when engine turned off, but gets up to correct height front and rear when car is started.

This will be the first change of these rear spheres. Car now done 53000miles. Front two spheres were changed at 36000miles by main dealer in 2008, but not centre front.

Any observations?

Xaccers · Unread post by **Xaccers** » 03 Aug 2010, 23:36

Forte's the newer name for LX isn't it?
So I take it you've bought two non-hydractive and one anti-sink sphere?
Easy to tell them apart, the corner spheres have a small hole, and the anti-sink has a large threaded hole.

rmunns · Unread post by **rmunns** » 04 Aug 2010, 00:39

They are from ebay.fr and cost €79 inc postage for the three.

Unread post by **citroenxm** » 04 Aug 2010, 15:12

The common mis conception there...

The rear sphere is not an "Anti Sink" sphere, but a rear brake reserve sphere... you'll possibly find changing this sphere will NOT make any difference to the sinking, as the sinking is controlled by the smaller 5 way valve thats on the side of the "anti sink" sphere bracket..

Theres other posts on here, and experiance with one of my own, of anti sink cars sinking after the engine'd stopped, when I had this on a VSX I changed EVERYTHING and I mean everything from a working car that stayed up, and it still sank!... Only things I didn't change was the rear struts... my guess is though, that your anti sink VALVE is not closing off after a system pressure drop... to shut the struts out and hold the car up....

Paul

Unread post by **Old-Guy** » 08 Aug 2010, 18:44

citroenxm wrote:The common mis conception there...

The rear sphere is not an "Anti Sink" sphere, but a rear brake reserve sphere... you'll possibly find changing this sphere will NOT make any difference to the sinking, as the sinking is controlled by the smaller 5 way valve thats on the side of the "anti sink" sphere bracket..

Paul

However, the rear brakes are powered from the rear suspension circuit (to provide load compensation). So at rest, the 'Anti-sink' sphere does provide a reserve of pressure to maintain ride height (for a while).

I would agree that the root cause of a 'non-sinker' sinking while parked is the anti-sink valve not doing its job of isolating the rear height control valve. The significance of this is that the height control valve is designed to leak internally to provide adequate lubrication as it's in constant motion when the car is moving. Without the anti-sink valve, pressure would fairly soon leak away when the engine wasn't running (as it does on BXs and very early Xantias).

But to shut smartly and positively when the engine stops, the Anti-sink Valve requires on a local reserve of pressure from the Anti-sink Sphere. So a knackered anti-sink Sphere WILL cause a non-sinker sink when parked, albeit indirectly.

Unread post by **citroenxm** » 08 Aug 2010, 19:09

Sorry Old-guy - I still have to disagree after the plavar I had with a VSX I had with anti sink...

As I said I swapped EVERYHING from a car that didn't sink, and it still dropped like a stone as soon as the engine was swapped..

What you will find with a Flat anti sink sphere is the car should still stay up with engine off, but you WILL find that when the engine is started the rear Will drop down untill the pump has built pressure up again to lift the rear..

Again, this is known from fact with my OWN TD SX with anti sink and original "anti Sink" sphere!!!

Paul

Unread post by **xantia_v6** » 08 Aug 2010, 19:18

Old-Guy wrote: However, the rear brakes are powered from the rear suspension circuit (to provide load compensation). So at rest, the 'Anti-sink' sphere does provide a reserve of pressure to maintain ride height (for a while).

My recollection from an earlier discussion is that when the anti-sink valve is closed, the "anti-sink" sphere is connected to the brakes, but disconnected from the suspension, so it can't help the suspension stay up.

Unread post by **Old-Guy** » 08 Aug 2010, 19:32

Different cars, different experiences. When I first had my 96 Sx estate, it had a habit of sometimes sinking at the rear.

Agreed, it did tend to rapidly hit the floor as soon as the engine was started and then rise back up quite quickly.

Then the N/S/R sphere blew so I replaced the whole set on the grounds that they were all original (c. 75,000 miles and 12 years). Not only did this improve the ride enormously, but it cured the intermittent sinking.

I did of course, empty the reservoir (while the system was depressurised) and then flush the brake lines. A certain amount of cr4p came out with the ancient LHM that might have been part of the problem.

Interestingly, I noticed with amazement that the dead (won't start) VSX that I'm dismantling still rose to HIGH even after a 150 mile collection trip on a trailer.

addo · Unread post by **addo** » 09 Aug 2010, 00:14

It's my belief that standing (residual) pressure in the accumulator has a lot to do with whether a car sinks.

If the regulator is duff, it may be clicking off before correct pressure is reached in the storage side. As a consequence, you then lack stored fluid energy to hold the other side of your antisink valves shut against pressure fed back from the suspension corners.

rmunns · Unread post by **rmunns** » 09 Aug 2010, 05:34

Thx for interesting replies.

But I'm not much wiser.

My car sinks on switch-off. From the service records (one previous owner, FSH main dealer) it has had just two front spheres. But fluid is clean.

Car seems not to be carpet-ride, you do feel the bumps. Seemsto be at rear.

Rear arrangement at the anti-sink sphere is coated in grease.

Main problem is not knowing whether I have a problem or not. Too many times I've tried to improve something only to find it weren't broke in the first place!

Would someone please write how we know if it''s worth changing parts or fluid or greasing or adjusting etc.

I know this is not simple, but I think a lot of us need to know which symptoms are worth investigating.

addo · Unread post by **addo** » 09 Aug 2010, 07:06

Fluid generally looks "clean" save for the brake caliper ends which can become a little brownish yellow. Overall, though, on a Xantia fluid colour is no indicator of hydraulic health.

You need to have all spheres pressure tested. There is no other test which accurately quantifies their condition.

Make sure you are not confusing "sinks at switch off" with "returns to normal height after exiting vehicle". To be more certain of rapid sinking, switch off the car and remain inside for several minutes, to see if it sinks. To check slow sinking, measure wheelarch heights a minute after exiting, and then several hours later.

Should the accumulator sphere be dead flat or near this point, I suggest having the pressure regulator and pump independently checked.