Short Life on Rear Spheres

[Gregg1100]

Hi All,
This last May, I changed rear spheres. This week I have found rear end getting very bumpy. I didn't change rear hydractive sphere or the anti sink (wasn't sinking) at the time.
Should I have changed the hydractive one at same time as the other two?? Rear end hard to push down at corners and no bounce back. Accumulator changed a bit before May, but hardly hear it ckick at all.

Car is 97 Xantia 16v, 2 litre VSX Hydractive
Regards,
Greg
Ps. 94 Xant TD nearly ready for road (1st Nov ). No hydractive, no aircon, no all but useless front fog/spot lights. Just a common old Lx with 201,337 miles under belt.

[AndersDK]

Brandnew or recon spheres ?

Antisink sphere is for rear brakes safety spare pressure accumulator only.
Even if the hydractive (center) rear sphere was dead flat - you should still have the basic suspension from the wheel spheres. Meaning the press down test would perform as it should.

NOTE : It is imperative to do the Citaerobics extensively from time to time (every 2-3 months) - to ensure any trapped air is drawn back to the reservoir.

[Mandrake]

Even if the hydractive (center) rear sphere was dead flat - you should still have the basic suspension from the wheel spheres. Meaning the press down test would perform as it should.

I think thats a bit misleading.

Even though the outer (wheel) spheres in a Hydractive 2 model have similar gas pressures to those in non-Hydractive 2 models, the damping valves are calibrated to be VERY stiff, and so those spheres can't really be evaluated by a simple bounce test -

Simply pressing the body down by hand can't exert enough dynamic force to open the threshold valves in the dampers so the movement is heavily restricted by the very small bypass hole (which is only this small in Hydractive spheres) - the result is that it feels very stiff like there is little gas even when the gas is fine. Also the rebound will be very slow taking as much as second or two to return to the nominal height.

Because of this it is the centre sphere with its lightly calibrated damping valves and high pressure that provides the majority of the "soft" feeling when doing a manual bounce test, so if this sphere is flat it will make a big difference to the feel of a bounce test.

So in answer to the original question - yes you should have changed the Hydractive centre sphere at the same time as the outer two - the 3 spheres work together as a team in the soft mode, and if either the strut spheres or the centre sphere are flat it will have consequences on the ride quality.

A quick test to check the centre sphere is to try a bounce test in both hard and soft modes.

So first let the engine idle and try bouncing the rear suspension in the "soft" mode - it should be extremely soft allowing you to press it down to the bump stops with ease, and if you bounce it up and down it will feel quite lively.

Now turn the ignition off and make sure all doors including the tailgate are closed for at least 30 seconds and it will switch to hard mode - now try the same bounce test at the back with it in the "hard" mode and you'll find it will be MUCH stiffer, on the order of 3x or more, and will feel more like the suspension in a sports car.

If it seems stiff in both "soft" and "hard" mode, or the soft mode is only a little bit softer, the centre sphere needs replacing.

As Anders says, the anti-sink sphere should have no effect on ride.

Regards,
Simon