Hi,

my XM needs a new accumulator sphere and whilst replacing that, I'm thinking maybe of replacing others too. Particularly, the front is rather in need of replacement. Apart from the 2 suspension spheres, I believe the XM has a 3rd sphere on the front suspension. I'm not sure what this is about and wonder whether someone could explain it to me and recommend whether I ought to replace that as well.

Thanks

Andrew

Also, I believe gsfcarparts.com is a good source on the internet, any other recommendations would be much appreciated..

Thanks

Andrew

Hi Andrew,

The number of spheres you have and the exact function depends on the model and year of your car. Why not add the details of the car to your signature so we can give you some accurate guidance?

The 3rd sphere is the additional one added to the suspension system when Hydractive suspension came about. Prior to that, each wheel had an associated sphere. The pressurised gas inside acts like a spring in a normal suspension system and in the neck of each sphere there is a series of holes which act as the dampening function just like a shock absorber on a normal car.

When they invented Hydractive they needed a way to be able to switch the suspension from a nice soft mode for cruising to a hard mode for turning corners quickly (soft suspension is no good for turning corners, you'd end up in the field or worse, through Sainsbury's front window). To achieve this they added another sphere in parallel to the exisiting ones on each axle. The middle one is separated from the hydraulic circuit by an electrically actuated valve (an electrovalve). When the valve is open all three spheres together provide the soft suspension mode. When the cars brain (ecu) detects that you are turning a corner it quickly shuts off the center sphere by closing the electrovalve. Only the two wheel spheres remain open. These now have a much higher damping effect than the wheel spheres before Hydractive came in. The suspension behaves much stiffer with only two spheres open. Once around the corner the ecu opens the valve again and the suspension returns to soft mode. Its equally important for the center, hydractive, sphere to be fully charged as it is the wheel spheres.

Each axle has an additional sphere for hydractive suspension.

GSF certainly gets a good report for spheres although I cant comment directly never having bought any from them. Are you relying on mail order?

Where in the country (or world) are you?

Cheers

noz

Hi Noz,

thanks for the information. Presumably the same is the case for the rear suspension?

I live in Andover in Hampshire. I'd prefer mail order really unless I can buy locally.

Thanks

Andrew

Hi andrew,

Yes the Hydractive theory is the same for both axles.

Do you intend to fit the spheres yourself? Do you have a sphere removal tool? Are you aware of the procedure to depressurise before removal?

Cheers

noz

Hi Noz,

no, my local garage has said they will fit them for me. They're not bothered if I buy them - they suggested it actually. I'm not really a diehard car freak, I look after making sure it is properly cleaned, especially at the end of winter to get salt off, and regularly serviced and but I leave it at that. Thankfully so far, work has been mostly limited to servicing, I see all sorts of horrors of people spending thousands on goodness knows what!

Thanks

Andrew