how soft should the rear be?

[chinkostu]

recently had the rears done on the car, the old ones weren't flat but were definately past best. new ones on and its soft, but almost comically soft, sitting in the boot it hits the bump stops... i'm assured the spheres are right but theres not tell-tale marks, short of taking them off and checking them against a known rear sphere. HC works beautifully in bringing it back up though so no real issues with people getting in and out


i've obviously been used to the not so soft spheres and the ride is definately comfier but this seems almost overly soft, or do we reckon theres a catastrophic air pocket that needs bleeding out?

[CitroJim]

It should be soft but perhaps not that soft Stu...

It's worth checking he damper element leaf valves (the discs visible on the end of the sphere). I've known these work loose on regassed spheres and cause exactly this fault. At first it had me scratching my head for ages...

This really affects the damping and makes the rear-end very boat-like!

Also, check the pressures... They may be blown up too high... Known that on regassed spheres too...

Finally, advise the diameter of the centre hole...

[chinkostu]

It should be soft but perhaps not that soft Stu...

It's worth checking he damper element leaf valves (the discs visible on the end of the sphere). I've known these work loose on regassed spheres and cause exactly this fault. At first it had me scratching my head for ages...

This really affects the damping and makes the rear-end very boat-like!

Also, check the pressures... They may be blown up too high... Known that on regassed spheres too...

Finally, advise the diameter of the centre hole...

need to find someone with a sphere tester then

guessing if its the valves they have to go back as I can't see any way of repairing them!!

The only thing I can think of is them being front spheres, although i'm guessing they would be even worse (higher pressure aren't they?)

i'll have to whip them out and see, time to get mucky

[CitroJim]

Stu, there's a thread on here somewhere with those of us with sphere testers...

Shame I'm so distant from you...

[chinkostu]

Stu, there's a thread on here somewhere with those of us with sphere testers...

Shame I'm so distant from you...

I've done that distance and back before once in a day, don't think I can do it again

I'll have a mosey Cheers!

[white exec]

Also try bleeding the rear suspension (on the XM - Xantia same? - this is done by bleeding the rear brakes) - air in that part could cause excessive softness as it compresses.

[CitroJim]

Yes, good point Chris

Same method as on the XM exactly...

[chinkostu]

Also try bleeding the rear suspension (on the XM - Xantia same? - this is done by bleeding the rear brakes) - air in that part could cause excessive softness as it compresses.

brake bleeding is on the cards with the hydroflush, so will try that thanks! I always forget the two are connected

[CitroJim]

Yes, always when swapping rear spheres always bleed as they are effectively at hydraulic dead-ends, unlike the front spheres..

A really good dose of Citraobics may help too...

[chinkostu]

Yes, always when swapping rear spheres always bleed as they are effectively at hydraulic dead-ends, unlike the front spheres..

A really good dose of Citraobics may help too...

Good job i've got some free time I thought the rears would still get some fluid movement at least?

Can actually do the bloody dogbone finally as well

Cheers again guys, i'll try bleeding and a good citroebic session before pulling things apart.

[Mandrake]

IMHO it won't be air that needs bleeding - there's no way that air in the system would cause it to be comically soft or affect how far it sinks when you sit on it. In fact air in the system would make the ride unbearably harsh over potholes.

Check that you don't have 40 bar estate spheres fitted on the rear of a hatchback - this will make it comically soft. Hatchback rear spheres should be 30 bars. (Post a part number if you can find one)

However in my opinion depending on how heavy you are (I'm about 90Kg) its normal for the rear suspension to bottom to the bump stops if you sit on the edge of the boot, even in a non Hydractive model.

A Hydractive model is even softer - I can bottom the rear suspension just pushing it down with my hands! This is normal...

Maybe you have never seen the suspension perform with good spheres ?

[CitroJim]

Air is compressible though Simon. Think of spongy conventional brakes that need bleeding and how they feel.. Soft and squidgy..

A bleed is always a good idea, if only to get air out of the brake lines. Don't forget a lot needs to be bled as the piping goes from back to front (to the dosuer and ABS) and then back again so don't be afraid to bleed a lot. Save on LHM by attaching a long tube to the blood nipples and piping it straight back to the reservoir.

Bleed then until you see no more air and always bleed on high with the rear suspension loaded. You cannot over-bleed...

[Mandrake]

Air is compressible though Simon. Think of spongy conventional brakes that need bleeding and how they feel.. Soft and squidgy..

Sorry but I can't agree in this case Jim. Yes air is compressible, but you can't get enough air into the suspension during a sphere change to cause the suspension to compress down to the bump stops when a person sits on it when it otherwise wouldn't have.

Brakes are a different situation because they are not under pressure all the time so when there is no brake pressure the air is able to expand to its normal volume and then must be compressed down again next time you press the brakes, and because they're a dead end circuit this compression and expansion of the air will keep happening every time you apply the brakes.

The suspension is completely different - when the car is up there is always pressure in the suspension. Imagine that 20cc of air got in when the spheres were screwed in place - the air in the end of the cylinder and sphere neck. As soon as the suspension is pressurised it will be at about 100 bars (80 for the rear, 120 for the front) which will compress that 20cc of air down to about 0.2cc when under normal suspension pressure - an infinitesimal gas volume compared to the approx 200-300cc of active gas volume in a 450cc sphere, so it can't contribute anything significant to the springing compliance of the suspension. (But it will cause ride harshness due to causing cavitation between the piston and damper valve)

Also I assume that the car has been up and down a few times since the spheres were fitted so the suspension should have self bled by now but it sounds like it is still just as soft.

A bleed is always a good idea, if only to get air out of the brake lines. Don't forget a lot needs to be bled as the piping goes from back to front (to the dosuer and ABS) and then back again so don't be afraid to bleed a lot. Save on LHM by attaching a long tube to the blood nipples and piping it straight back to the reservoir.

Bleed then until you see no more air and always bleed on high with the rear suspension loaded. You cannot over-bleed...

Yes its important to bleed the system but it's not going to make any difference the suspension bottoming when sitting in the boot.

I await chinkostu's post that confirms this after he has bled everything.

[chinkostu]

However in my opinion depending on how heavy you are (I'm about 90Kg) its normal for the rear suspension to bottom to the bump stops if you sit on the edge of the boot, even in a non Hydractive model.

A Hydractive model is even softer - I can bottom the rear suspension just pushing it down with my hands! This is normal...

Maybe you have never seen the suspension perform with good spheres ?

I'm not the lightest of people

[CitroJim]

It's good to give this subject a good airing (sorry, no pun intended ) and debated.

Like you Simon, I'll be most interested in the outcome. Always happy when it's proved I've just talked a right load of old bollocks (or should that be spheres? )