Hydractive Suspension Height Correction Speed?

Unread post by **CitroJim** » 25 Mar 2007, 10:48

Yesterday I gave our Xantia SX TD a good checkover ready for its first Caravan tug of the season next weekend. All was perfect

I was flabbergasted, nay staggered, at how quickly the suspension rose up to max height on the lever (checking LHM level) and how quickly it went down, up again and back to normal height whilst doing citarobics. It was RAPID. the TD is a very early non-anti-sink non-hydractive non-anything.

In comparason, my Activa is positively slow and pedantic at responding to height changes on the lever. It does it fine but it is so slow to do so, almost painfully

The STOP light oftem comes on during citarobics.

Is this due to the 2 piston pump (vs 6 piston on the TD) or do I need to go and give the height correctors some TLC as discussed in other posts?

DickieG · Unread post by **DickieG** » 25 Mar 2007, 11:00

Jim it's a combination of looking at extreme's here.

The early model Xantia's positively leap into the air compared to anti-sink models due to a much larger output from the pump being totally directed towards the suspenion via the flow direction valve, whereas anti-sink models only have two pistons on the pump to pressurise the suspension.

Then add up that the early model has only five sphere's whereas your Activa has ten, in addition to a high pressure 'balancing' circuit, should say it all really.

Unread post by **philhoward** » 25 Mar 2007, 11:20

I was going to reply to this one, but Dickie has said it all!

Mandrake · Unread post by **Mandrake** » 25 Mar 2007, 12:22

The early model rising much quicker is definately due to the single output pump vs the two output pump. As well as my 1997 with Hydractive 2 we also have a 1993 (with one output pump) and a 1994 (with two output pump) both non Hydractive 2 and the difference between the two for lifting speed is stagering.

I really think Citroen dropped the ball with this one - no reason why they couldn't have done anti-sink WITH the single output pump! (Resulting in a car that is topped up and ready to drive VERY quickly!)

From fully depressurized an anti-sink Xantia takes longer than a GS to lift, and the GS although lighter only had a one piston pump!

Does anyone know the reasoning behind the move to a 2 output pump and elimination of the FDV ? Was there something inherantly unreliable about the FDV system ?

However falling quickly seems to be related to (lack of) Hydractive 2 - both the non-Hydractive 2 cars drop very quickly at the rear when lowering the height, but my Hydractive 2 is positively pedestrian at going down at the rear, and that can't be the pump...(and no, the height corrector is not seized)

Regards,
Simon

DickieG · Unread post by **DickieG** » 25 Mar 2007, 13:31

Mandrake wrote:Does anyone know the reasoning behind the move to a 2 output pump and elimination of the FDV ? Was there something inherantly unreliable about the FDV system ?

However falling quickly seems to be related to (lack of) Hydractive 2 - both the non-Hydractive 2 cars drop very quickly at the rear when lowering the height, but my Hydractive 2 is positively pedestrian at going down at the rear, and that can't be the pump...(and no, the height corrector is not seized)

Regards,
Simon

As far as I recall FDV's weren't the most reliable item's, taking a look through some older post's may confirm this.

I have noticed that its quite common for anti-sink Xantia's to be quite slow dropping right down onto the bump stop's at the rear. I wonder whether it's due to a combination of the rear arm bearings becoming stiff and the running surface on the rear struts becoming dirty due to the lack of movement across the full range of movement, due to anti-sink. Hence why I regularly perform 'Citerobics' on mine.

Unread post by **CitroJim** » 25 Mar 2007, 14:11

Thanks all, I really do enjoy it when a thread really goes into good technical depth

I really think Citroen dropped the ball with this one - no reason why they couldn't have done anti-sink WITH the single output pump! (Resulting in a car that is topped up and ready to drive VERY quickly!)

Simon, I agree with that statement very strongly, it does seem strange. Had they used the big pump with an FDV we would then enjoy the best of both worlds and maybe even Citroen would have fully removed from peoples minds the twin criticism of waiting for the suspension to rise AND waiting for the STOP lamp to extinguish. Who knows, the system might have survived into the C5 and beyond then.

I cannot imagine the two-output pump was any cheaper to produce nor that dropping the FDV was cheaper for them. In my opinion, it was a good system.

Thinking, maybe the two-output pump is a little more reliable in that a failure of the PAS system does not impact upon braking and suspension as it can on an FDV equipped car. Imagine if the PAS took all the pressure and denied the braking and suspension then with anti-sink you'd not feel the suspension go down to warn you and next thing, no brakes. I don't know, just a theory. You'd have to studiously ignore the STOP lamp of course in such a scenario but what if it was blown anyway. I guess car makers have to take every eventuality into account where there could be a compromise to safety.

deian · Unread post by **deian** » 25 Mar 2007, 16:06

I agree, i've seen my friends N reg 1.9td VSX (with old spheres) and old pump fly up, and fall down before you could say 'hydractive two', I was amazed! And quite jealous.

Mine is 'more graceful'... more than a minute to go from low down to high up, you couldn't do the up/down thing as traffic lights with the later ones, if it was down and it changed to green then it's not safe to move (no brakes or scuff tyres on corners and lack of comfort).

Total stab in the dark here...

Could it be something to do with the need for lighter steering on the later pumps? So if there is an extra output (which goes to the power steering on the later pumps) doesn't this suggest they may have wanted to enhance the feeling, reliability or handling on the (later) cars that came with the 6+2 pump?

Maybe they wanted to dupe the returning potential 'citroen' customer into thinking... the the steering 'does' feel lighter (therefore making the car 'feel' more reponsive?) compared to their older citroen. Maybe it was supposed to be a special selling point. Or thinking even further, the lighter steering would affect the body roll more therefore making the sensors (i.e bodyroll sensor) react quicker and making the car feel sportier on the corners (another selling point)?

Could it be something as vague as that?

jeremy · Unread post by **jeremy** » 25 Mar 2007, 16:33

Its like a BX - and if it rises rapidly you've got flat spheres - simple as that!