Xm suddenly drops while sitting still?

[robbocop33]

Hi,i bought a 2.1td XM(mk1) a couple of months ago and something is quite strange.The suspension goes up and down great,really quick,but say if i put it all the way up,then back down to the normal riding position,switch the car off,the car will sit there,then suddenly will drop quite violently a few inches,then maybe again a little and will end up where it should be?anyone any ideas?All spheres are new on the car,new LHM fluid.

[NiSk]

Sounds like either the front struts are a bit sticky at the extremes of upper travel (if it's the front) or that the rear suspension arm bearings are starting to show their age (if it's the rear). The front can be dealt with quite easily by pulling the plastic gaiter down when at highest setting and lubricating the piston shaft with some LHM. The rear is quite another problem.

//NiSk

[andmcit]

Hi,i bought a 2.1td XM(mk1) a couple of months ago and something is quite strange.The suspension goes up and down great,really quick,but say if i put it all the way up,then back down to the normal riding position,switch the car off,the car will sit there,then suddenly will drop quite violently a few inches,then maybe again a little and will end up where it should be?anyone any ideas?All spheres are new on the car,new LHM fluid.

Now I may have this all wrong, but as nobody else has posted a view yet I may as well have my pennesworth and generate some discussion!!

The drop of the car is a result of a step in the pressure between the corner spheres and the middle ones [one each end] that add the hydractive extra damping. What effectively is happening is the pressure is being maintained in the normal corner spheres and the pressure is released into the full circuit when the electrovalve that controls the hydractive opens.

Suddenly the pressure that OK and managing to cope with holding the car up opens into an extra circuit with low pressure - thus what's holding everything up is reduced...and it drops down very noticeably.

When you say you'vE had ALL the spheres done, does this include the difficult to see centre pair on the subframes?

It may be hocum but that's what I've gleaned along the way and as a theory it does explain things a bit better than other suggestions!!

Andrew

[NiSk]

Ahh- I was assuming it was a no-hydractive (early series I td). Perhaps you can tell us robb? (does it have a "sports" button to the left of the gear lever).

/NiSk

[Peter.N.]

..Or it could just be that the height control valve linkage is sticking.

[robbocop33]

Its a series one car with the sport/normal switch to the left of the Autobox lever,incidentally the car just drops at the front,not the rear.

[andmcit]

For the car to effectively lose pressure so suddenly allowing it to drop at one end only suggests a loss of high pressure in the front circuit. As the car raises and lowers smoothly I recon the strut will be fine though there could still be a leak of fluid from it - worth checking the returns from both.

I'd expect the accumulator would have been changed being easy to access but the middle sphere and electrovalve at the front would still be my key suspect. The front does have pretty much 60-70% of the car's weight so if the hydraulic pump isn't up to it will feel any ill effects in the hydraulics first though.

Sticking Flow distributor valve? As you mention new fluid has been used it still wouldn't hurt to change the reservoir for hydraflush in case there is crap blocking the feed/return pipework though that's more clutching at straws.

Andrew

[AndersDK]

We have had this discussion before.

The HC can not dump the pressure fast enough to make the car "jump" down. The HC would only make the car calmly sink down - and so would any antisink valve.

The only part of the circuit which have internal capacity to move such pressure so fast is the Hydractive suspension system. Its got 10mm dia piping - and an extra sphere to dump the pressure into.
Its typical of a failing hydractive block.
My guess its the infamous O-ring seal at the valve.