Suspension Height Control Linkage

[marc61]

Hi,

I'm really pleased I discovered your site recently - lots of useful stuff here for the XM! I think I'm in the category of long term sufferers, trying various things to get my XM's suspension back to what it should be and never quite getting there.

I've replaced all spheres except the anti-sink, cleaned filters and used the flushing fluid for about 2000 miles, soldered diodes into the hydractive brain and replaced both height correctors! Each time there was a noticeable improvement for a while, but not a lasting solution. The cars a 2.5TD and has done 180,000 miles - I've done the last 50,000.

I'm not convinced its a hydraulic problem and am now starting to think that it might be the mechanical linkage from the suspension height control lever inside the car to the height correctors causing some mechanical restriction. Does that make any sense?

I've noticed the front is a lot smoother if when I start up I select high, then once it gets there I put it in normal. When I do this though I think the back stays up a little too high and the rear runs harder. Its like something is stopping the car from running at its correct height front and rear, and the problem is allowed to be either at the front or at the rear but not both! All of which makes me think its mechanical not hydraulic.

Does anyone know if the linkage can get bent or siezed up somewhere? Does it need adjustment/greasing? I've tried spraying WD40 at it but to no effect and access is a pain.

Any suggestions appreciated as I really would like to solve this before we get to the 200,000 mark!

Cheers

[noz]

Hi Marc,

Welcome to club-xm. I hope you find it a useful resource for keeping your XM on the road. You'll find it a friendly place with plenty of help and advice on offer from fellow XM owners.

Your suspension problem is a common one. But to diagnose the root of the problem we need to drill down to it via a series of questions and possibly tests. Please bear with us and don't get too despondent if we don't get to it on the first pass.

Firstly, the electrovalves which control whether the centre spheres are either in-circuit or out of circuit make a buzzing sound when they are energised. This is because the signal being sent to them is not a constant dc signal. Its a PWM signal with vibrates at approx 1000Hz. With the engine off, open the drivers door. You should hear a noticeable 'clunk' and then a constant buzzing sound. You may have to stick your head under the car to determine whether its coming from the front or the back or both. If the valves are buzzing then it suggests that the electrovalves are OK and that the ECU is OK (pending one more test). If the diodes in the electrovalves are bust then the ecu will be able to energise the electrovalves for a little while until the Solid State Relays inside overheat then they will switch off as a self-protection mechanism. When they cool back down they operate again. Therefore intermittent operation of the SSR's is symptomatic of bust diodes. I see that you've already installed new diodes. Can I just confirm (and please don't be offended) that they are fitted the right way around and that the signal is getting to the electrovalves rather than being shorted out inside the ecu?

If you open the drivers door and leave it open the electrovalve should buzz continuously for two minutes and then they will switch off so as not to drain the battery. Closing and opening the door should energise them for a further two minutes. If the buzzing sound is not there or is not continuous then you have ecu trouble (or cabling from the ecu to electrovalves or electrovalves themselves).

The height corrector linkage has no bearing on how hard or soft the suspension is unless they don't operate at all and the suspension is on the bottom bump stops.

Please let us know the results of the above and we'll tackle the next step.

Cheers

noz

[demag]

Hi marc61,

Welcome to the club, or should that be join the club!

There are a number of us on here in a similar situation to yourself. All passing information back and forth in an effort to try and resolve the suspension problem. You will find some very interesting and informative posts relating to this on the site.

Good luck and stick with it. I'm sure we'll all get sorted out.

[Andmcit]

Wouldn't an incorrectly adjusted ride height on the anti roll bar have the car
operating in an incorrect range of the the suspension travel causing harshness
to the ride as it tops or bottoms out sooner than desired?

Andrew

[wirdy]

Welcome marc61, you're joining a group of us searching for the panacea to give us the consistent soft suspension we all feel now & again.

Seems like you've done a fair bit of fault diagnosis by elimination so far and you're joining the debate at about the same point as the rest of us..........have a look at the hydraflush / hydranet discussion thread.

Andy - If the ride height was that far out it wouldn't it be obvious from just looking at the car?

[Andmcit]

Fair point and I'm joining what sounds like a long running discussion totally cold. The
comments made by Marc61 about an improvement to ride when the hight is adjusted
and the car being visibly out from what 'feels right' may have given a clue!?

One of my Xantia TD estates is prone to have a lower back end running height after
I'd changed the rear height corrector and has an effect of giving a harsher ride and
even harshness sometimes like it's bottoming out but an adjust of the selector linkage
seems to stir it into the correct attitude where it then runs OK and rides well - the room
for optimum adjustment seems very critical as it's nearly right on the car!

I'm happy to defer to you guys to nail this issue!!!

Andrew

This post has been edited by Andmcit on March 13, 2008 12:21 am

[marc61]

Thanks guys. I've got the clunk and the buzz. The buzz seems to last a long time if I leave drivers door open, but it only lasts about 15s on the front and 30s on the rear after I shut the door.

Will check those diodes.

Cheers

Marc

[marc61]

Photo of diodes I fitted in hydractive box attached.

I think I've got them the right way round ??

Cheers

Marc