Hi,
All info in these posts is OK - strap wrench, release pressure beforehand etc, just like a hydropneumatic Citroen. I'd like to add:
- the release torque on the sphere will be around 40 lbs-ft-f - not very tight, but enough to call for a 1' lever for comfort;
- Citroen spheres are gas springs, filled with nitrogen at around 70-75 bar pressure. They lose 5-7 bar per year due to 'porosity' effects (molecular interstitial losses across the membrane), and need to be recharged every 4 years or so in order to keep the system they're fitted to in proper working order. If they lose sufficient pressure (due to neglect), the internal diaphragm gets punctured and the sphere is then a write-off (and would have to be replaced rather than refilled);
- you should check the level of the (presumably green LHM) suspension fluid before you start work on the sphere: because if the sphere's diaphragm is punctured, a certain amount of fluid will have migrated into the space previously occupied by the inert gas filler and will be lost when you unscrew the sphere from the axle housing;
- if there are other spheres on the axle (I don't know the GRx4, but there may be) bear in mind that they'll be in the same state as the accumulator sphere and will also need to be replaced;
- after seeing your website photos, I'd suggest most strongly that you consider replacing the hydraulic pipes as well as the sphere, as soon as you can, using cupro-nickel or Kunifer piping. I've found that this material works very well on Citroen suspension repairs because it's malleable and corrosion-resistant;
- if your brake pipes are in a similar state to the hydraulic pipes, I'd get those changed at the same time (using the same material - cupro-nickel). I realise that the cost of doing this work might actually be uneconomic, considering the age of the car - but it might be a lot cheaper than a sudden and unexpected MOT failure. If you feel inclined to keep your costs down by trying to do the work yourself, I can say that the only specialised tools you'll require will be a Sykes-Pickavant Flaring tool (or similar), with a supplementary die set that's been made especially for flaring the smaller-bore Citroen hydraulic piping (see below) - and a decent bench vice to hold it steady;
- if you need to buy replacement spheres, cupro-nickel piping (and the special pipe-flaring die set), and replacement hydraulic unions and rubber seals, one company that would probably help you is
http://www.pleiades.uk.com/. I've had good dealings with them on all occasions in the past, and would deal with them again anytime;
- the hydraulic suspension system on hydro Citroens is self-bleeding: you simply exercise it a few times to flush any trapped air back into the fluid reservoir (where it can escape), and that's it. However, the rear brake hydraulic circuit is usually supplied from the rear suspension hydraulic circuit (via the brake-pedal demand-valve), in order to make sure that rear brake power is regulated in direct proportion to rear-axle load. As a result, air (or gas) introduced to the suspension circuit can find its way into the rear brakes, and defeat how they should work - so it's necessary to bleed those items separately in order to make sure that all air has been eliminated. If *your* rear axle system is set up like this, you need to bear this in mind as well. Personally, I'd get the manual and see what's in store before making any decisions.
Good luck.
Regards,
Philip Andrews
(If it is not very stuck)