Suspension Problems, boing boing boing

sorry i havent posted for a while, self employed and all that. i have a problem with my latest 2.0i XM sx, on an N reg it pushes down on each corner fairly easily but when driving it feels like the rear spheres are completly flat . when you drive over a speed bump, the back end bottoms out then jumps, almost taking my fillings out,the front is not much better, i have noticed that when you turn the ignition on there is only one click from under the car, could the electro valv for the rear ctr sphere be faulty ,if so would it cause these simptoms,ive also noticed that if you drop the suspension right down, on raising it ,it some times comes up with a jerk : HELP,,,,,terry

Have you checked the height of the suspension? could be you have a sticking rear height corrector valve, if so, give it a good squirt of WD40, you may have to do this several times but they usually free up eventually.

Peter.N.

Terry,

As you drive over a bump the piston inside the pump pushes the fluid into the sphere(s). When the car has passed the bump and the wheel is on the way back down, this is where the damper comes in. The damper only works when the fluid is on the way out of the sphere. If I take from your description that the gas charge would seem to be OK on the surface then I suggest the one-way part of the damper in one or more of your spheres is U/S or has dirt stuck under the seat preventing it closing. This would explain the 'jump' after the bump.

However, the bit I don't understand about your explanaton is the knocking your fillings out part. This would suggest that, as you go over a bump, the wheel rises towards the car and instead of the spring part of the sphere absorbing the disturbance it is transmitted to the body of the car. You would then be propelled upwards. As the car starts coming down again, your body is still travelling upwards and you hit your head off the roof.

Does the car sit the correct height above the ground especially at the back?

There are two electrovalves for the Hydractive. They should both switch on together when standing still. It's a bit difficult to tell them apart when they activate at the same time. You need to get your head undr the car at the same time as someone turning on the ignition to determine if one or other of the valves is not working.

If the rear electrovalve is not working then this will certainly explain your symptoms. The rear suspension will feel like the kind of car lesser mortals have to put up with.

Hope this helps.

Cheers

Noz

nos/ thanks for replying ,as to my fillings ,ive been driving over speed bumps and potholes for a couple of days now at different speeds, and am coming to the conclusion that if the front wheels hit a bump at speed the back drops when it reaches the same bump then as the back of the car bottoms out it suddenly jumps, if i go over them at about 15 mph alls fine?? wha i cant understand is that if i accelerate hard from a stand still the back has no suspension and is hard but does not jump up,,,, thinking out loud,,, could the rear spheres be flat, and when stationary or driven carefully its using the ctr sphere as suspension, then when i hit a bump the ctr sphere is locked out , ie/sport mode, then sudenly come back in with a jump as the body rises at the topof the rebound????? ,,,,,,cheers terry

terry,

hmmm, a difficult one without actually seeing it first hand. The 'jumping' bit may have an explanation. Taking one axle say the rear. There are three spheres (ignore the antisink for a moment). Say they are all at the same pressure and the car is level, moving or not. Say then that the electrovalve on the centre sphere closes. The original pressure is trapped inside the sphere. Now, in the meantime say the pressure in the other two spheres drops. This could happen if the height corrector thinks the car is too high and lets some pressure out of the system. You may also have a leak in a strut which is passing fluid back to the reservoir.

Anyway, something causes the circuit to lose pressure. Now the system is at a lower pressure than the centre sphere. The ecu opens the centre electrovalve (maybe going back into soft mode). Suddenly the stored pressure is released and shared by all 3 spheres and the result is a sudden 'jump'.

Very flat spheres with almost no gas left in them may explain your symptoms. Pushing down on each corner would make everything look OK as long as there was at least some gas left in the sphere. But when it comes to the amount of fluid displacement when going over a bump, maybe you're bottoming out on a flat sphere.

This isn't really an explanation just a mind jogger to try to interpret the symptoms. The true reason for your troubles will become apparent when you analyse whats happening in fine detail. To do that, it helps to understand how the whole thing is meant to work.

Sometimes just brainstorming the problem finds the solution without necessarily understanding the whole thing. Certainly more deteil increses the likelyhood of finding a solution.

Hope this helps

noz

cheers noz im going to get under the car today if weather permits, both electro valves are working i can hear them when hanging out of the door and turning on the ignition, ive noticed the rear of the car sometims drops when turning on the ignition???? i think ill replace all three rear spheres, the anti sink seems ok as the car stays up for a couple of days, the front hight adjuster is a little stiff ,as i cant always get it to go to full hight at the front, wd40,to the ready, ill keep you all posted,,,,terry