C5 Hydractive 3+ :Strange Suspension behaviour

fred1 · Post by **fred1** » 11 Feb 2009, 19:03

Hi,

Just had my rear suspension arm bearings replaced by my local garage (too cold and wet to do it myself!!).

Job went ok, they de-pressurised the system at front and rear vent points, did one side at a time so no need to fully remove the anti roll bar or disturb the rear height sensor.

However, on completion and system re-pressurised and topped up, the rear suspension "hunts" up and down about +- 15mm in the normal height position. It also does not seem to fully rise at the rear in the high position. Xenon headlights also hunt up and down on their automatic adjusters.

Have tried "citrobics" and "bouncing" on the tow bar at various height settings and their is a slight improvement in height but not stability.

I suspect air in the system.

Any thoughts or suggestions ???

Regards

John

AndersDK · Post by **AndersDK** » 11 Feb 2009, 20:13

Air would be vented by the Citaerobics, so I doubt that is the problem.

I suspect that the rear height sensor has been disturbed in some way.
Its a simple electronic potientiometer just like a throtte position potientiometer, so its not really complicated to figure out if its working correctly.

If the linkage or the pot itself is sticking you would get this symptom.
Also I believe if the pot has worn a hole in the resistor element it would cause a hunting height setting, as the correct setting might be exactly in that hole.

The pot is not overly expensive (£50ish) and quite easy to replace.

fred1 · Post by **fred1** » 12 Feb 2009, 06:54

Hi Anders,

Thanks for the thoughts, I wondered the same thing. However, not sure why it should have suddenly appeared unless the it had worn over time and the failing/failed arm bearings (and they were bad) had effectively been providing increasing damping in the system and broadened the null point? Fixing the bearings

By the way I assume the system works by a height change moving the AR bar which moves the pot and puts an "error" signal into the height controller which then moves the suspension height to cancel out the error.

So the "null" point on the potentiometer is always at the same position for any stable height and thats why the hunting takes place at both normal and intermediate height settings and only at fully or fully down is it stable.

So I assume that I can't do a temporary fix by moving the AR bracket a bit, the system will just adjust to end up with the pot at the same null point!

Perhaps I coould try a small resistor in series with the pot just to prove the point before trying to change it.

Any ideas on how else to confirm the cause?

Regards

John

In fact I have to leave it in low when not in use otherwise it would "hunt" all night!!!

steelcityuk · Post by **steelcityuk** » 12 Feb 2009, 14:27

You could connect up a Lexia and setup the suspension to a different height that may give some idea.

Steve.

AndersDK · Post by **AndersDK** » 12 Feb 2009, 20:31

John you got a point there -

The position pot can not be worn out all over the track, only at the most common position.

If continued Citaerobics does not help, I fear you will need your Citroen specialist, popping on the Lexia tester.

Could be the BSI unit at fault with a leaking rear suspension electrovalve because of some dirt/foreign material trapped in the valve.
That fits the bill of the hunting height, i.e. pressure leaking back, position sensor sensing missing height, valve opens to compensate and so on etc. etc.

The leakback plastic pipes from the rear cylinders could not possibly carry such a huge pressure loss, causing the suspension to hunt.
The plastic pipes would instantly pop off or burst.

fred1 · Post by **fred1** » 13 Feb 2009, 11:24

Guys,

Thanks for the input and thoughts

Have decided to try changing the rear sensor pot, seems most liklely cause and only £30, looks relatively straight forward to fit and local Cit garage has one available.

The problem appeared immediately after the bearings were changed, that is as soon as the car was started. So I favour a pre-existing condition that had developed over a period but was being "masked" by the extra stiffness/damping of the failed/failing bearings.

Will let you know how things progress.

John

fred1 · Post by **fred1** » 13 Feb 2009, 17:20

Success!!!!

Changed the sensor pot and problems gone away.

Very straight forward job.

Local garage that did the rear arm bearings let me use their hoist.

Disconnect battery,
Pop off linkage
Disconnect plug
undo 8mm bolt
slide pot off bracket
Slide on new pot, put bolt back, reconnect plug and linkage.
Reconnect battery

I suspect their may be a number of C5 about with "worn" pots, in fact mine "nods" occasionally at the front but does not "hunt" ! So should probably change that one some time.

Thanks for all the thoughts and suggestions

John

AndersDK · Post by **AndersDK** » 14 Feb 2009, 15:45

Many thanks for your feedback John - much appreciated $\:D/$

BTW : whats the mileage of your C5, as this could be a good future pointer for strange C5 suspension behaviour.

fred1 · Post by **fred1** » 14 Feb 2009, 16:23

Anders

Mileage is 140k - just about right for rear bearing arms.

My Xantia 1.9TD 1993 is due for a second time at 360k

Regards

John

Post by **myglaren** » 14 Feb 2009, 17:34

Mine at 127,000 doesn't seem to be having any problems. Can't say what may have occurred in it's past life of course but there was no indication in the receipts that came with it of anything other than the steering UJ.

I have had the rear screen latch solenoid wires repaired, the rear calipers done - before they needed it, corrosion was minimal.
Replaced the blower control module a couple of months ago, at the last service had the camshaft drive belt components and water pump renewed.

Apart from a slightly weepy bellows unit on the rear suspension being replaced, a couple of exhaust bits, new front discs and pads all round - all wear and tear items, plus new tyres and steering ball joints as a result of being forced off the road, that's pretty much it.

The aircon and trip computer both conked out the day I bought it, regassing the aircon fixed the first, the other is really not a problem but may fix it one day.
One thing I would like to work is the rain sensor to control the wiper speed a little more flexibly and shut the windows when I forget (all the time) but again, hardly important.

Fuel economy isn't great, mainly around 32mpg, which is partly my driving style and partly all the very short trips I do. Considerably better on longer runs but still not as good as the Xantia 1.9 TD.

Running on Shell V-Power currently and although the car is a bit more perky it certainly hasn't done anything for the economy, which is decidedly worse.

ETA:

And of course this diatribe is in completely the wrong thread, as per usual.