Citaerobics oddities

Toby_HDi · Unread post by **Toby_HDi** » 10 May 2010, 20:17

For a while now my Activa has made soft knocking and groaning sounds when doing Citaerobics. At first I thought was air but 10 healthy spheres, Hydraflush and a brake bleed later it still does it.

It is more prounounced when moving from high to low but does it to some extent when going the other way.

Today, whilst doing a second session on moving the height lever back to normal from high the front end just collapsed down with a bang before bringing itself up to normal height. Quite alarming! :shocked:

Any ideas? All I can think of is maybe sticky correctors and wear in the guide rods, but I would have thought the latter would only affect Activa balancing part of the system.

Unread post by **CitroJim** » 10 May 2010, 20:24

You're on the right lines there Toby. If you have read my blog lately you will see from my trials and tribulations that the Activa system can have funny effects on ride height and the behaviour of the front height corrector.

Was the car leaning rather appreciably when it collapsed?

Toby_HDi · Unread post by **Toby_HDi** » 10 May 2010, 20:59

Can't say I had noticed Jim, I think it does lean slightly.

It just collapsed suddenly about a second after I moved the lever from high to normal.

I do recall you saying yesterday about it all being interdependent.

I fear I may need to look at the lean, as well as the HC's, roll corrector and the guide rods.

Unread post by **CitroJim** » 11 May 2010, 20:47

Toby, I've been thinking about this issue for a while and this evening I did some tests. My project Activa had spent some time on high this evening whilst I bled the brakes and gave it a final check-over before MOT.

When I set the height lever back to normal, it was a little reluctant at first to drop at the front and then, all of a sudden it did what yours did but it did not crash down. It fell from full high to about mid-way between low and normal and bounced softly at the bottom if you see what I mean. It did not crash down. It then quite quickly assumed normal ride height and level. It fell more or less level.

I'd say that as the engine was running and it was in soft mode that the bounce and soft landing was due to the cushioning effect of the centre hydractive sphere. Have you had your centre sphere checked/replaced as I'd be tempted to suggest it may be a bit flat perhaps. Else that or the front corners are a little flat.

So why does it happen? I cannot offer any concrete explanation but I've seen this before on Activas but I cannot recall having seen it on a normal hydractive or ordinary Xantia.

On full height, the Activa rams will be well extended and I know from my trials of setting the level that a ram can hold the front high due to how the ram operates on the anti-roll bar and on the front height corrector. My thought is that as the rear starts to fall, the rear ram starts to compress and sends pressure to the front ram. This has the effect of keeping the front high but putting the front HC into a lower position as the ram and drop link assume unequal lengths. Also as the front starts to fall, this will have an effect on the roll corrector and all of a sudden the small movement applied to the roll corrector will cause the ram pressures to equalise and then the front can fall further. because the height corrector was already in the lower position, pressure will already have drained from the struts so as soon as the rams equalise themselves there is nothing to prevent a sudden fall.

As I say, if the spheres are good at the front, it should result in a soft bounce.

Therefore I have to say a sudden, well damped fall is a normal Activa quirk.

Having said that, do check the spheres and check that the roll corrector quadrant mechanism and front height corrector mechanism is well lubricated and operating freely. The roll corrector quadrant has a habit of seizing up if not kept lubricated and in regular use.

I'd also give the front strut pistons a bit of lubrication as well.

Hope that helps Toby...

Toby_HDi · Unread post by **Toby_HDi** » 11 May 2010, 20:52

Excellent Jim, thank you very much.

Seems that my thinking on the sticky correctors could be the cause. It is disconcerting though. I'll look into giving them a clean and a grease.

All spheres are healthy, they were tested at Richards and flat ones replaced about 2 months ago.

Maybe with some more use it'll be fine. Its been stood uninsured for the last month or so. Hopefully that'll be rectified this week.

Koukku · Unread post by **Koukku** » 12 May 2010, 10:16

CitroJim wrote: On full height, the Activa rams will be well extended and I know from my trials of setting the level that a ram can hold the front high due to how the ram operates on the anti-roll bar and on the front height corrector. My thought is that as the rear starts to fall, the rear ram starts to compress and sends pressure to the front ram. This has the effect of keeping the front high but putting the front HC into a lower position as the ram and drop link assume unequal lengths. Also as the front starts to fall, this will have an effect on the roll corrector and all of a sudden the small movement applied to the roll corrector will cause the ram pressures to equalise and then the front can fall further. because the height corrector was already in the lower position, pressure will already have drained from the struts so as soon as the rams equalise themselves there is nothing to prevent a sudden fall.

Therefore I have to say a sudden, well damped fall is a normal Activa quirk.

Took me a while to wrap my brain around that explanation

My Activa sometimes does the opposite while going down from full height... at about half way down the front jumps up a bit, and then continues to fall normally. I guess it's also caused by roll corrector movement while the front is falling.

Unread post by **aerodynamica** » 12 May 2010, 17:54

Today, whilst doing a second session on moving the height lever back to normal from high the front end just collapsed down with a bang before bringing itself up to normal height. Quite alarming! :shocked:

I should say: All hydraulic Citroens can do this - if the car is set to high height then moved back or forward, the tyres become wedged against the outward force of the suspension moving down (the front track width changes you see) and causes the height to lower slower than the height corrector wants, result: the LHM pressure is still flowing out when the car is still up and causes it to fall suddenly below the normal running height.

It can also result in the front suspension doing a crazy up-down-up-down cycle caused by the wedging of the tyres making it overshoot and correct but never find the middle position until you either move the car forwards (resolving the wedging effect) or turn the steering (resolving the wedging by torque thru the wheel hub.

Anyway, I'd check this first in case it is simply this phenomenon.

KevMayer · Unread post by **KevMayer** » 14 May 2010, 18:07

I have a theory:- See what you think....

Could the front stuts being a little bit sticky and needing to be greased be the problem.

As you move the height lever to a lower setting the height corrector will call for LHM to leave the front truts. Sphere diaphragm compression would normally be unchanged as the height changes. The diaphragm deflection will just depend on the car's weight. But, if the creaking struts aren't free to slide then the front end could be held up on the struts. The sphere diaphragms will then begin to move out as the car lowers and will provide decreasing contribution to support the weight, until the contribution of the spheres reaches a point where the struts suddenly slide resulting in a sudden drop.

Unread post by **CitroJim** » 15 May 2010, 21:46

That sounds very reasonable to me Kev, especially as the struts are up in a position they rarely see in normal use so will be a bit sticky at the extreme end of its travel.

And coupled with what Graeme so clearly describes, I reckon the full answer...

aerodynamica wrote:I should say: All hydraulic Citroens can do this - if the car is set to high height then moved back or forward, the tyres become wedged against the outward force of the suspension moving down (the front track width changes you see) and causes the height to lower slower than the height corrector wants, result: the LHM pressure is still flowing out when the car is still up and causes it to fall suddenly below the normal running height.

The problem of McPherson strut type suspensions. I imagine this was never a problem on Citroens pre-BX with double wishbones.

I just cannot ever recall seeing it of a non-Activa Xantia though.

6speedmanual · Unread post by **6speedmanual** » 22 Dec 2012, 18:27

Hi
(bit of a thread resurection, but can add.....)

I have seen this "drop" behaviour on my SX - basic spec suspension.
The car is high mileage 160k and may not have see "high" for a while.
I cleaned the front strut rams and removed a build up of gritty clart from under the gaitors. Lubed with ACF50 and reinstalled the gaitors. The rams were in vgc without scoring or wear marks.
A few up down cycles showed problem to have gone.
It also creaked and lowered in series of slight judders. This was simply the FARB bushes. A squirt of WD40 got rid of the noise.
I have since rebushed front end. Up and down now smooth.

Peter

French Car Forum

Citaerobics oddities

Citaerobics oddities

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