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I hope someone can help diagnose the recent problem that's developed on my car.

Every now an then the rear of the car drops quite suddenly (to below normal drive height). When moving this is usually brought about by going over a hump. Within a few seconds it recovers to normal height.

The same thing sometimes happens when waiting in traffic - but normally only if I'm pointing downhill. For example - I'll be sitting in a queue with my foot on the brake (no parking brake applied). I won't be aware that anything unusual is going on until I release the brake at which point the rear dips down quite dramatically and then immediately recovers within a few seconds.

When the problem started (about 7k miles ago @ 65k miles) it was very infrequent but is now happening more regularly.

One other point I should mention which may or may not be related: when I park the car and apply the parking brake and am walking away from the car - there's a slow creaking noise for a few seconds as the car seems to settle slightly.

By the way all 8 spheres are new, LHM has been flushed & replaced, LHM filter has been cleaned and height adjusters greased up.

I suspect it's the rear suspension arm bearings that are going - can anyone confirm / offer an alternative? Does anyone have any experience of replacing these bearings?

Many thanks

Hi Roy.

I'm sure you'll get plenty of input regarding the hydraulics. Just a quick point on changing the bearings -- once you have the arm (s) off and the centre pin out, you're left with the issue of extracting the bearing seats. In the absence of a special tool, I used an old head bolt, the type with a small flange as an integral part of the head. I found the flange just engaged the lip of the bearing seat nicely and after moving around the seats and getting them started, a couple of good whacks at opposing points had them out in no time.

If you've got ABS, don't even think of trying to get the sensor out of the arm (unless you only put them in yesterday !). Find the connector and disconnect and bring it out with the arm. On mine, (2.1), the RH connector block was a real b*****d to get back in. Exhaust in way, axle beam in way, bad temper in way, etc. etc. etc ! Good luck.


I should add that my arms were in good order; if the seats have given out or churned around, you might have more of a struggle.

Hi Roy,

Remote diagnosis of hydraulic problems is never easy but maybe the following will spark a thought or two. I'll take your points easiest first.

As Mike and yourself say the squeak at the back end is almost certainly rear swinging arm bearings. Removal and replacement is not the worst job in the world but there is one pig to watch out for. The strut has a steel rod inside which connects the piston to the swinging arm. At the arm end it finishes in a half cup ball and socket joint (for rotation) and a small parallel protuberance with a hole bored through it. This lines up with the holes bored acrossways on the arm itself. A spring steel clip is then pushed through the first hole in the arm(alloy), through the steel rod protuberance and eventually out the other hole in the arm(alloy again). Guess what? The spring steel clip and the alloy corrode badly and the clip gets stuck in place. Its the worst part of the job getting the pin out. You could go through an entire swear box before it lets go. The second to worst part would have been getting the sphere off but since thats been off recently it should be a doddle. The third item to look out for when removing the arm is the support for the brake pipe which is bolted to the arm. The bolts 8 or 10mm A/F) are almost certain to shear unless you are very lucky. However, when the arm is out on the bench the sheared bolt can be heated and withdrawn. The final item is the bolts which hold the anti-roll bar onto the arm. They are very tight and put in with superglue. That means that after you have got them turning you'll need a socket all the way to the last thread. A real bore. If the squeaking has only just started the bearings should not be so shot that its damaged the outer race recess as Mike pointed out. I can get my struts out in 15mins from a standing start. The arm shouldn't take much longer than that (my clips are all new and well greased).

Next is the sudden drop whilst waiting in traffic.
As you approach the lights you gently press on the brake. The rear end naturally lifts due to the geometry of the trailing rear arms. After coming to a stop you continue to keep your foot resting on the brake. We all do because the parking brake is a pain to operate and its much less effort to keep your foot on the brake. The back end is too high because, with the brakes on, the wheel cannot rotate and the swinging arm cannot return to its normal position. During the time that the body is too high the height corrector is bleeding pressure (fluid) back to the LHM tank because its the only way it knows how to reduce the height. But the body does not follow the reducing presure downwards because the brakes are preventing the wheels from rotating. The lights turn to green and you let your foot off the brake. Suddenly the wheel can now rotate and there's no pressure to hold the body up since its been leaking away through the height corrector back to the tank. The body drops at the back and you pick away from the lights. Due to the increased engine revs and the fact that the height corrector now sees that the body is too low the HC admits fluid very quickly to the rear struts and the body returns to its normal height. The next time you pull up at the lights put on the parking brake and see if it happens again. If not, you've found the problem.

Lastly - the sudden drop after a bump.
This is hardest to diagnose but here's my theory. You've replaced all 8 spheres (presumably with known pressure new ones?) so that eliminates some possibilities. The fact that it happens just after a bump leads me to believe that the rear struts or strut seals are worn. My hypothesis is that going over a bump the compressed fluid in the strut suddenly increases in pressure since the displaced fluid cannot pass through the jet in the sphere fast enough. This temporary rise in pressure exerted on the seals causes the first seal to temporarily pass fluid. I say the first seal because if it was the second seal also then you'd find LHM all over the road. As such the fluid is jetted back to the LHM tank usually causing spillage at the tank end. After the bump has passed the fluid can only be replaced relatively slowly so temporalily the back end drops quite low. The low body height is sensed by the HC and more fluid is admitted to the circuit thus correcting the deficit. Anyway, thats my theory. Check the LHM tank lid for signs of splashing out due to the bursts of pressure release back to the tank.

Hope thats given you something to think about.


noz cool.gif
See this link for some pics of the bearing replacement job.

Unfortunately rolleyes.gif I cannot help with the rust issues that you will have in the work area as we do not have that problem in Aus. Salt on roads? Only if someone dropped their chips unsure.gif

There are some ex UK cars in Aus and the owners continually face corrosion challeneges.

BTW - some of the symptoms you explained, including creaking noises were evident in my car before the bearing job. They have gone now. wink.gif
Thanks Mike, Noz and Craig,

OK then rear swinging arm bearings need replaced - we seem to agree.

Thanks for the tips on this job Mike and Noz - and for the excellent photos Craig. I don't have anywhere indoors to do this job myself though so I've asked the local indy for a price!

Noz - thanks for explaining the sudden drop at the lights issue.

I'm a bit more worried about your suggestion that the seals in the rear struts are gone though (as you might imagine). I've had a quick look at the LHM tank and there doesn't seem to be any sign of leakage at all. I had hoped the sudden drop might also have been the arm bearings. I may need to pay a bit more attention to the circumstances under which it does this. The problem is it doesn't happen very often. I've noticed it as I said when going over a hump - but I don't think it's the only time.

I'd better get to the bottom of this if the indy is going to have the struts out anyway. What's the solution if the strut seals need replaced? Is there a kit or is it a case of recon units (sounds very expensive)? I remember a rear strut going on my Mk1 2.1TD about 7 years ago - lots of LHM on the road - but the car had done about 300k+ at the time! It wasn't cheap to repair if I recall - and I had to get it recovered on a low loader of course.

Craig - you said:

BTW - some of the symptoms you explained, including creaking noises were evident in my car before the bearing job. They have gone now.

I don't suppose sudden drop at the rear was one of the symptoms your rear arm bearings sorted out (ever the optimist)?

Thanks again,

Hi Roy,

The seal thing is only a theory based on your description of the symptoms. I realise that in such a new car it's probablility is low. Maybe with closer study another option may present itself. The seals are a doddle to change if you need to get the strut out anyway. Pleiades sell them individually. To install, simply remove the concertina boot of the strut and pull the piston out. Just make sure the nylon 'o-ring' / rubber o-ring combination goes in the right slot and in the right order. Just take note from the original locations.

Considering what they are they were expensive. Pleiades charge £3 per seal. In my case they sent the wrong ones the first time (wrong diameter). When I phoned them to tell them that they were wrong they just shrugged their shoulders and sent me the right ones. They didn't ask for the other ones to be returned. I guess they have so little value in reality that it wasn't worth the postage to send them back.

Watch the diameter though. I think there's a difference between the estate and saloon and between the V6/2.5 and all the other models.

Cheers and best of luck.

noz cool.gif
Hi All

I have one car that exhibited in a big way the back dropping symptoms at lights and rear end bouncing on speed humps and big dips. It has been SORN now for a couple of years so I did not join in in the early stages because of no recent experience. There is one thing about this that worries me and that is car mileage. Mine with the problems is the 2.5 car with only 50k on the clock. Now it also had one of the rear cylinders replaced (leaking LHM) when I bought it at 30k miles.
I am concerned that substantial work with an indy at cost is proposed an I am not sure we know the cause of real problems.


Hi XMexc,

I agree with you - and I certainly don't want to be paying the indy unless it's really necessary. However - one of the things that's pushing me to get this checked out is that I need 4 new tyres and if the bearings are gone the rears are likely to wear on the inside. (Can't really tell from the tyres that are on now because they came off my previous car that went to the breakers, and they've been swapped around too - although there are some signs of wear to the inside.)

I had another suggestion too - that it might be the firmness regulator valve (onto which the rear centre sphere goes) sticking and suddenly releasing that's causing the drop. The suggestion came from someone with a Xantia VSX who found this same problem - but only first thing in the morning - the rest of the day the car was fine. I notice mine tends to drop quite often when the car's cold - but does it at other times too I think. As you and Noz rightly say a bit more careful attention to the circumstances in which it does this is needed before making a decision to spend money with the indy.

Perhaps the centre sphere valve sounds more promising though. What do you all think?

I had the car at Marsh Citroen when on holiday in the summer and Dave Alstin had a good look at it and couldn't find anything. He also has a Xantia that does exactly the same thing - and he's never got to the bottom of the problem himself either!

I also need to pay more attention to the creaking noise coming from the car when I park it up - i.e. to establish exactly where that's coming from - that would help! It's been suggested that rear bearing failure would likely cause creaking when starting the car up in the morning - as it rises, and perhaps when going along the road too - and I don't get either.

As a slight aside - I discovered Pleiades do replacement rear suspension arms @ £135+VAT. However - they machine out the apertures where the bearings sit and fit collars as they say when the bearings go they almost always damage the arms too. In addition when they re-assemble the bearings the tube between the bearings is oil filled to prevent the possibility of them going again.

Indy estimates £230 to do both rear bearings. This based on 4 hours labour plus 2 bearing kits.

I've checked as best I can to see if there's any sign of the rear wheels leaning in at the top / out at the bottom - but can't detect any.

More careful checking needed then!

Thanks to all for your input so far.

Hi Roy

I have just been out in the V6 auto (135k) and stood on the brake at the traffic lights. I noticed the back rise slowly but there was no sudden drop on pull away, it just softly resumed normal height. This car has no recorded rear suspension work in its history and is not fitted with antisink. Now antisink can cause sudden drops when the car is stationary even when the system is working correctly. It would be interesting to know if the Xantia with problems has antisink fitted.
I will repeat the brake test with the R reg 2.5 estate (135k) when I get the chance. If the rain stops I will put the second set of HID's on it later today. I have a drivable scrap P reg 2.5 estate (135k) and if I can start it I will take that round the unit roadways, hold it on the brake and play on the speed bumps.
With the low mileage 2.5 I have always had a problem with speed bumps that I do not notice to the extent of making back seat passengers heads hit the roof. This is at speeds that I expect a normal XM to glide over and with a brand new cylinder fitted to the passenger rear by a Citroen main dealer. I know they fitted new because it went up on the ramp to show me the work done and all removed parts were laid out on the new parts boxes in the boot. They felt I was a most untrusting individual and only stopped my complaining by offering to take the car back and refund all my money.


Hi John,

Thanks for your message. I'm not really that worried about the drop when at the lights - it's probably within normal range - as Noz explained to me. I mentioned it though in case it shed any light on the "sudden drop when in motion" issue.

My car has anti-sink - but I don't know about the Xantia.

I don't even think there's a problem with speed bumps - it seems to glide over them OK - although it's the kids who're normally in the back - and if anything they'd be urging me to go over (the tummy bumps) faster - so not very discerning passengers as far as diagnosing this problem goes I'm afraid.

The problem seems to be on the open road. I've been thinking about when I can recall it happening and I'm pretty sure it tends to be 1) as I'm pulling away, 2) when going over a (gentle) hump in the road and 3) probably tends to happen more when the car's cold. I'll be paying more careful attention over the next few days to see if I can narrow it down more - and I'll investigate the creaking when I park up too.

I appreciate your help again.

Best wishes

Hi Roy and all.

I'd take issue with the view that the arms will nearly always be damaged if the bearings are gone. I've done the job a few times on the BX and twice on XMs and only in one instance was there any significant arm damage. I think if you act in good time, it's normally OK. Got my last kits from GSF and they were very reasonable - can't recall exactly, but under £40 for the two arms, I think. A long, long way off £130 odd a shot.
The real weakness is in the basic design. If you think about it, the wear is continually on less than a one quarter segment of the track and rollers, yet they use a device designed for rotation at umpteen thousand rpm. I suspect it doesn't really matter how much oil or grease you refill them with (I use oil, too), the basics are just wrong and they will periodically need changing. It should have been a proper fulcrum shaft with a proper full length, greasable bronze bush in the arm. Still, don't suppose they'll modify it now !!

Hi Roy et al,

Rear arm bearings
Personally I would not entertain the 'kit' which consists of two taper roller bearings, the distance tube, the long bolt and the nylock nut. Unless you have run the car a long time with knackered bearings enough to damage the alloy (a common sight in CX's) then most of the kit will not be required. The last time I bought the bearings they were £6 each. Even today they are about £9 from GSF. But they are a standard bearing and can be bought from any bearing stockist. The distance tube, bolt and nut will all be reusable.
To diagnose the bearings jack the car up and depressurise (or the other way around). The wheels should be hanging under their own weight. Remove both road wheels to reduce the slung weight. Now lift each wheel in turn. This will be slightly difficult at first until you have pushed any remaining fluid out of the strut. After that it should be fairly easy. Both wheels will tend to lift because they are connected by the anti-roll bar. Through your hands you should be able to 'feel' the bearing as the trailing arm rotates about the centre bolt. You should also be able to judge how freely the arms move both up and down. If the races are pitted or badly worn you should feel the ridges as the hub rises and falls.

Sudden Drop (forgive me...thinking out loud)
OK lets take this logically. The body remains at a given height due to the perfect balance between gas pressure and fluid pressure. On the basis that the gas can't escape easily lets assume its fixed. Now, if the body suddenly (or otherwise)falls then fluid must be removed from the system somehow. IF the LHM doesn't appear on the drive it must return to the tank. Therefore the paths which the fluid can take or limited. Anti-sink valve, Height Corrector, Centre Electrovalve, Strut Seal failure.

Seal Failure
We talked about that before

Height Corrector
Known to be pretty simple and reliable devices the HC has only a limited capability to allow depressurisation 'quickly'. A fair judge of this is when you move the height control lever from high to low. The speed at which the body falls is limited to the rate at which the HC can spill fluid back to the tank. Is a 'Sudden Drop' faster or slower than this. If faster then it suggests the HC is not to blame unless very badly worn inside.

Centre Electrovalve
For the back end to 'suddenly drop' when the electrovalve opens it presumes it was empty during the time when the wheel spheres were fully pressurised. Upon the opening of the electrovalve the fluid int he wheel spheres rushes across to the empty centre sphere and thus fluid is subtracted from the wheel circuits causing the body to drop. What would cause the centre sphere to be empty? Possibly after sitting all night the spheres do depressurise. When the engine starts in the morning the wheel spheres are filled. However a fault in the circuit which feeds the electrovalve may keep it closed whereby its pressure remains low. You drive away and at some later tim ethe electrovalve decides to open. The back end drops due to the sudden lack of fluid until the pump recovers the situation. This should happen only once per journey though if this is the problem. A contiuously running pump should not allow this to happen mid-journey.

The anti-sink system consists of a one way valve and an additional sphere. The valve is purely mechanical and has no associated electrics. I don't understand this system well enough to think through the logic of the sudden drop but it doesn't seem likely.

No answers but more food for thought.


noz cool.gif
I have just come back to XM ownership after around 5 years without. I had the back drop while sitting with foot on brake at the lights symptom on my last 1996 XM. Nothing to to with letting the wheels move - the back just drops then rises again. I would swear I fixed it last time but can't remember how - so annoying as I have it on this XM too. A good night of sipping wine and I am sure it will come back to me.

As for rear bearings. I did these on my previous 1991 Si. They were so bad that the tyres were rubbing on the inner "boot" wheel arch. The bearing sockets were all eaten away in places by what was left of the old bearing but still held the replacement bearing fine.
Been reading a Technical Spec for Citroens and when it came to brakes it said that the ABS system can open a valve to take pressure of the brakes very quickly. I think this is what causes the back to drop so suddenly. I had ABS problems on the last XM with the rear dropping and fixed them so perhaps that is what I did to stop the problem. Will find out shortly as I have the car going in for a diagnostics reading on Monday partly for the ABS and partly in the hope that there is a software update available for the Autobox.
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