Hi Guys,
I've had an R-reg 3.0V6 Exclusive for around 18 months. When I first got it, it was a dream to drive. A while ago the car developed a bouncy (hard) rear end esp. when going over speed humps (lots round our way). Not as it mounted the hump but as the back end comes off. The car seems to drop like a stone off the smallest of humps. It can take quite a while for this to recover leaving you with an unconfortable journey. Sometimes this happens at the start of a journey, (my drive is on a slight slope and the car faces down the slope) and you can feel the backend drop a few hundred yards up the road, then a nice smooth ride (until the first speed hump). There seems to be no LHM leaks and it's topped up ok. I'm not sure about the switch near the gear selector. The light on it doesn't come on and I don't seem to notice any difference when it's pushed.
Any ideas please?
Xantia Exclusive Rear Suspension Bounce
Moderator: RichardW
Garry -
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">and I don't seem to notice any difference when it's pushed<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
- you mean caning the car, or the push down test on the suspension [:o)]
I remember we had a previous thread on this mysterious rear end dropping on a Hydractive XM I believe.
Your descriptions on symptoms are exactly the same ...
- i.e. sudden rear drop on minor road obstacles.
Unfortunately we never did come to conclusion on this problem.
A few facts :
Your V6 is pr def. a HI-end model, and then would have both the hydractive (HA) and rear anti-sink system fitted.
The HA system spheres are recognised by their 2 un-usual large diameter rigid pipes connected, and these spheres are found under the rear and in the corner of the engine bay.
The rear anti-sink sphere is recognised by a single standard 3.5mm diameter rigid pipe connected, and this sphere is also found under the rear.
So much for the fitting.
Now to the function :
Let's roughly finish off the rear anti-sink system.
The anti-sink system has a hydraulic operated valve fitted to the rear suspension circuit. This valve is ONLY controlled by the hydraulic pressures present in the rear suspension circuits - no external controls.
It's function is to isolate the rear suspension when car is parked.
When engine is running with normal system pressure present, this anti-sink valve has no function, i.e. it's constantly kept open by the present system pressure. Only when car is parked and then the system pressure after a while has dropped, this valve closes and then isolates the rear suspension circuit, preventing the rear drops by pressure loss while parked.
The anti-sink sphere has no influence on the rear suspension while engine is running with normal system pressure present. It's only provided as a rear suspension "memory storage" for the rear suspension pressure, once the car is parked. Thus it provides an isolated separate rear "suspension pressure memory" feed for the rear brakes, in the event the system pressure is lost during drive (as then the antisink valve THINKS the car is parked and isolates the rear suspension).
Let's roughly finish off the HA suspension system.
The HA suspension is in principle working by very simple means : it provides an extra suspension element which can be switched in or out - as simple as that.
An extra suspension element is then provided for each axle.
Thus you overcome the dilemma by having a soft supension, which makes the car dangerously unstable at speeds, by selecting either a comfortable suspension for LO speed, or a stiffer stable suspension at HI speed.
The complexity comes in WHEN this switching happens. This is decided by the HA computer, which in turn make decisions on sensor signals from several places on the car. It even overrides the drivers setting on the "mode" switch.
For safety means, the default (rest) mode is hard suspension, isolating the extra suspension element, thus leaving the suspension stable.
The extra suspension element (HA sphere) is switched in by an electrovalve in soft mode, controlled by the ECU.
Basically the soft mode is activated when the ignition is turned on, and then at speeds below approx 20mph. When ignition is turned off (parking) the soft mode is timed for approx 30seconds, then reverts to (non-powered inactive) default hard mode.
What could make the HA suspension fail ?
This has no definitive answers, as the hydraulic control elements involved are very complex.
Note : when talking leaks, I mean an internal leak back to the fluid reservoir, not external leaks dropping from components.
As the problem here is seen as a TOO soft rear suspension dropping down after bouncing over a road obstacle, it seems that somehow the rear suspension hydraulic pressure instantly is dumped somewhere.
This seems however unlikely to be possible, as no hydraulic connections OUT of the rear suspension system can provide for such instant pressure dumping, because of the small diam. 3.5mm pipes.
This in turn leads to the assumption that some of the pressure, from part of the system, is slowly leaking constantly during drive by a leaking control valve.
Then the HA hydraulic control valve instantly comes in as suspect part. This is contained within the sphere base for the HA sphere.
Let me try an argument for this :
The problem could be a leaking valve fuction, which isolates the extra suspension element, the HA sphere, during drive at speeds beyond approx 20mph. At such speeds, this valve is SUPPOSED to keep the HA sphere isolated, providing hard suspension mode.
on top of that, if we assume the faulty valve provides a constant slow leak path for the HA sphere, then this sphere is never kept charged to the rear suspension pressure.
If then, still assuming a faulty leaking valve, the HA valve block allows for a faulty continous soft mode, we then have the possible pressure dump path providing the rear intantly dropping.
This thought situation could be caused by one single function in the HA sphere valve block : the electrovalve leaking. Not by faulty electric control means, but purely by faulty hydraulic means.
From decades of DIY Citroen owners experiences, it's widely known that Citroen hydraulic valves are prone to faulty leaking operation, simply by dirt in the hydraulic system's fluid. This is a known consequence from ignoring hydraulic fluid services, or such work done ignorant by garages.
The valves themselves are known as incredible reliable components, rarely developing mechanical wear problems.
Overhauling/cleaning a Citroen hydraulic function valve is however prohibitive by professional means, because of the high garage rates, and doubtful warranty on the work.
There is a chance that a hydracleanse cure may solve this problem on your car. But such an attempt <font color="red"><i>must</i></font id="red"> be done prior to a possible replacing of the valve, since large riscs are that the new valve may be gunked up by dirt released by the hydracleanse cure.
Unforunately most garages can not do a correct hydracleanse cure, as they are not aware of this issue, thinks it's just another fluid replacement.
Try read my LHM fluid service.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">and I don't seem to notice any difference when it's pushed<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
- you mean caning the car, or the push down test on the suspension [:o)]
I remember we had a previous thread on this mysterious rear end dropping on a Hydractive XM I believe.
Your descriptions on symptoms are exactly the same ...
- i.e. sudden rear drop on minor road obstacles.
Unfortunately we never did come to conclusion on this problem.
A few facts :
Your V6 is pr def. a HI-end model, and then would have both the hydractive (HA) and rear anti-sink system fitted.
The HA system spheres are recognised by their 2 un-usual large diameter rigid pipes connected, and these spheres are found under the rear and in the corner of the engine bay.
The rear anti-sink sphere is recognised by a single standard 3.5mm diameter rigid pipe connected, and this sphere is also found under the rear.
So much for the fitting.
Now to the function :
Let's roughly finish off the rear anti-sink system.
The anti-sink system has a hydraulic operated valve fitted to the rear suspension circuit. This valve is ONLY controlled by the hydraulic pressures present in the rear suspension circuits - no external controls.
It's function is to isolate the rear suspension when car is parked.
When engine is running with normal system pressure present, this anti-sink valve has no function, i.e. it's constantly kept open by the present system pressure. Only when car is parked and then the system pressure after a while has dropped, this valve closes and then isolates the rear suspension circuit, preventing the rear drops by pressure loss while parked.
The anti-sink sphere has no influence on the rear suspension while engine is running with normal system pressure present. It's only provided as a rear suspension "memory storage" for the rear suspension pressure, once the car is parked. Thus it provides an isolated separate rear "suspension pressure memory" feed for the rear brakes, in the event the system pressure is lost during drive (as then the antisink valve THINKS the car is parked and isolates the rear suspension).
Let's roughly finish off the HA suspension system.
The HA suspension is in principle working by very simple means : it provides an extra suspension element which can be switched in or out - as simple as that.
An extra suspension element is then provided for each axle.
Thus you overcome the dilemma by having a soft supension, which makes the car dangerously unstable at speeds, by selecting either a comfortable suspension for LO speed, or a stiffer stable suspension at HI speed.
The complexity comes in WHEN this switching happens. This is decided by the HA computer, which in turn make decisions on sensor signals from several places on the car. It even overrides the drivers setting on the "mode" switch.
For safety means, the default (rest) mode is hard suspension, isolating the extra suspension element, thus leaving the suspension stable.
The extra suspension element (HA sphere) is switched in by an electrovalve in soft mode, controlled by the ECU.
Basically the soft mode is activated when the ignition is turned on, and then at speeds below approx 20mph. When ignition is turned off (parking) the soft mode is timed for approx 30seconds, then reverts to (non-powered inactive) default hard mode.
What could make the HA suspension fail ?
This has no definitive answers, as the hydraulic control elements involved are very complex.
Note : when talking leaks, I mean an internal leak back to the fluid reservoir, not external leaks dropping from components.
As the problem here is seen as a TOO soft rear suspension dropping down after bouncing over a road obstacle, it seems that somehow the rear suspension hydraulic pressure instantly is dumped somewhere.
This seems however unlikely to be possible, as no hydraulic connections OUT of the rear suspension system can provide for such instant pressure dumping, because of the small diam. 3.5mm pipes.
This in turn leads to the assumption that some of the pressure, from part of the system, is slowly leaking constantly during drive by a leaking control valve.
Then the HA hydraulic control valve instantly comes in as suspect part. This is contained within the sphere base for the HA sphere.
Let me try an argument for this :
The problem could be a leaking valve fuction, which isolates the extra suspension element, the HA sphere, during drive at speeds beyond approx 20mph. At such speeds, this valve is SUPPOSED to keep the HA sphere isolated, providing hard suspension mode.
on top of that, if we assume the faulty valve provides a constant slow leak path for the HA sphere, then this sphere is never kept charged to the rear suspension pressure.
If then, still assuming a faulty leaking valve, the HA valve block allows for a faulty continous soft mode, we then have the possible pressure dump path providing the rear intantly dropping.
This thought situation could be caused by one single function in the HA sphere valve block : the electrovalve leaking. Not by faulty electric control means, but purely by faulty hydraulic means.
From decades of DIY Citroen owners experiences, it's widely known that Citroen hydraulic valves are prone to faulty leaking operation, simply by dirt in the hydraulic system's fluid. This is a known consequence from ignoring hydraulic fluid services, or such work done ignorant by garages.
The valves themselves are known as incredible reliable components, rarely developing mechanical wear problems.
Overhauling/cleaning a Citroen hydraulic function valve is however prohibitive by professional means, because of the high garage rates, and doubtful warranty on the work.
There is a chance that a hydracleanse cure may solve this problem on your car. But such an attempt <font color="red"><i>must</i></font id="red"> be done prior to a possible replacing of the valve, since large riscs are that the new valve may be gunked up by dirt released by the hydracleanse cure.
Unforunately most garages can not do a correct hydracleanse cure, as they are not aware of this issue, thinks it's just another fluid replacement.
Try read my LHM fluid service.