Citroen XM Forum

Then I have sucesfully opend centre holes up with a 1.1mm NEW drill bit holding the sphere upright this too also made a nice soft ride from the spheres.

Must've been written in a hurry, but never mind. I've used precision drills to increase damper holes successfully on a BX 19GTi to make the damping a little smoother/softer. Holding the spheres upright/upside down is not really necessary. Gravity won't help a lot. Apply some grease to the drill bit and the metal particles adhere to it.

Once I have my charging rig up and running, I intend to play with the sphere pressures a bit.

As for the dampers, the spring washers are for sharp impacts , the centre hole is for longer duration bumps.

70 Bar pressure front spheres are for non-hydractive units. All UK cars are Hydractive.

I've got a sacrificial Xantia front corner sphere. I should cut a section to show the damper discs and centre hole so people appreciate better the role each plays. It's something I haven't found clearly illustrated online; there exist a few of the old Dee type removable damper blocs which are totally different but otherwise it's vague theoretical diagrams.

One thing worth bearing in mind is that the spring energy for a sphere can be measured in bar-litres, by multiplying the sphere's pressure by it's volume. So a 400cc sphere at 50 bar will behave similarly to a 500cc sphere at 40 bar. Replacing the 400cc sphere with a 500cc one at 50 bar will make things feel smoother on a good road, because the stored energy has been increased from 20 to 25 bar litres. So it's worth working out the bar-litres value if playing around with different spheres. I've used this to save money on the rear of my SM which should be running 700cc spheres at 26 bar (about 18 bar-litres), but is running with 400cc XM non-hydractive front spheres at 48bar (about 19 bar-litres). I've found you can't tell the difference providing you keep the bar-litres value about the same, and the damper hole sizes similar.

On the XM I've run with a 500cc centre sphere on the rear, makes it smoother and dive at the back when pulling off. But it bugged me and I went back to the normal 400cc. Ive never tried fitting 500cc corner spheres, suspect they're not available with the very small damper hole sizes for hydractive?

Final thought is it's the step change in both spring energy and damper area that makes the XM hydractive so good. On the front there's about 75 bar litres in circuit on a smooth road (40 bar litres for the 2 corner spheres plus 35 for the centre sphere), then suddenly when the centre sphere is taken out it drops from 75 to 40 and fluid can only access the spring energy via those tiny holes in the corner spheres. Hydraulically switches from limo to sports car in a split second, clever stuff!

Thanks for that Marc, sounds like youve done some work in this field : )

Addo you make a good point, i have access to a re gasser through work...i might give him a shout tomorrow...

Dieselman wrote:iirc, Your car is to be a 2.1Td, so, 62 Bar for the accumulator, 450cc-50bar-0.8mm damper for the fronts, 400cc-30Bar-0.7mm damper for the rears, 450cc-50Bar for the front centre and 400cc-50Bar for the rear centre.

Increasing pressure reduces the spring rate, making the damper larger alters the damping frequency.

Hi diesel man
Is there different pressures for the 2.5 estate? I'm doing one now and next a 2.0 CT turbo
Is there a pressure difference between models?
Thanks
Huw