This is common and is not a fault only a nuisance--it is because of the way the calipers sit. When in reverse, and you brake, the force on the assembly is in the opposite direction as when you drive forwards, and the small amount of play in the calipers make them clonk the other way. This also happens on Peugeots which also have the same assembly. Original brake pads behave better than cheap pattern ones.
Martin GUTKOWSKI
With all those various spheres and damper diameter holes, for any given Citroën model or even accross models, it is difficult to see at first how and why all these physical factors influence the suspension comfort.
Changing the LHM and rinsing the system is a part of normal service and care for all hydraulic Citroëns. Don't neglect this if you want reliable and trouble-free operation from you car. Dirt in the system eventually wears out some of the components if it's not dealt with in time. Although the system is extremely robust in itself, this does not mean that you should tempt fate.
There is a product called Hydraurinçage (sometimes also called HydraFlush, the French name is pronounced as \id-ro-ra[n]-sa'zh\ or, more precisely, using the IPA phonetic symbols: ɪdrɔrɛŋ'sɑ:ʒ). It's a special cleaning liquid manufactured by Total, orange in color; your nearest Citroën dealer is sure to have it on stock. The price is more or less the same as that of the regular LHM.
To start with, these are the spheres originally fitted:
The proper Citroën workshop manual method—in contrast to what the Haynes manual says—is to loosen the suspension sphere with a chain wrench ¼ turn while the system is still under pressure. Be very careful and absolutely sure that it is really only by a quarter of a turn. The pressure in the system is huge (the force behind the sphere can reach more than one ton, that is several thousand pounds), so opening it up with all that high pressure liquid behind it can be extremely dangerous.
A sphere is only as good as the neoprene membrane that contains the pressurized gas. Occasionally, the interface between the membrane and the retaining plate inside the sphere is to blame for leakages, but usually any problem is associated with the membrane itself. Like anything that's under constant flexing, it'll break down over time.
Release the hydraulic pressure pressure and undo all the conduits leading to the pressure regulator (have a rag handy, there is going to be a lot of LHM leaking out).
Put the distributor unit flat on a surface, so that the side with the two conduit sockets points upwards and the pressure adjustment screw (between two plugs on the side of the unit) is to the right, the side with the three conduit sockets will point downwards then.
You will need a seal kit (there are two such kits, part number 95 650 941 only contains the main piston seals while part number 95 597 221 has all necessary seals) and a slide bearing (part number 96 004 372) to rebuild each front strut.