Xantia rear end dropping cured.

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steviewonder7
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Joined: 08 May 2005, 01:02

Xantia rear end dropping cured.

Post by steviewonder7 » 16 Jan 2006, 22:20

Hi Folks,

Replacing my rear sphere's cured the xantia rear end dropping when coming to a stop.
I'll explain,when i first aquired the car I noticed that when driving the car and coming to a stop at 'T' junctions/roundabouts/zebra crossings etc etc,after a couple of seconds the rear end of the car would raise up to its normal height.This happened all the time.
After joining this forum I read that replacing the accumulator sphere may cure the rear end dropping and raising like it did.So I replaced the sphere and wadda you know rear end problem cured.
Anyway about a month ago(7 months after renewing the accumulator sphere) the same old problem reared its ugly head again..yep rear end dropping and raising again...so I thought not again!!!!! These accumulator spheres should last longer than this surely and the general opinion on the forum agreed with this.
The weekend just gone I needed to replace the rear suspension arms and hubs.I managed to renew only the offside rear arm and hub(the first time
I've done this),not an easy job by far.Anyway at the same time I decided to replace the rear suspension sphere's as a matter of course as I didnt know how long they had been on the car and they looked well old.Once every thing was back inplace hydraulics bled etc etc I took the car for a test drive and you know what, the rear end dropping and raising problem has disappeared.
There was me thinking I was in need of a new accumulator sphere.
So... I'm little confused (I dont really understand the workings of the hydraulic citroen),as to why at one time an accumulator sphere can cure the rear end dropping and raising and another time new rear sphere's can cure the same problem!
Steve :?

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Mandrake
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Xantia rear end dropping cured.

Post by Mandrake » 16 Jan 2006, 22:35

Hi Steve,

It's not entirely clear to me what your symptom was exactly, but I do know that it can't be caused by the main accumulator sphere being faulty. (And yes they should last at least 2 years)

Do you mean that when you brake at a stop the rear rises, (you may not actually notice this) and then a few seconds after you're stopped or if you ease off the brake pedal the car suddenly drops and then a few seconds later lifts again ?

If so thats just the rear brakes locking the rear suspension too high causing the height corrector to respond and let pressure out, then causing it to drop.

If I had to guess I would say your real problem was air in the rear brake lines - it relies entirely on the rear brake torque to prevent the car from lifting up at the back during braking.

As a demonstration try driving along normally (with no one behind you!) at about 50Km/hr (30Mi/hr) and then apply the hand brake as hard as you can. This is perfectly safe as it works on the same front brake pads as the foot brake.

You will notice that the rear suspension will completely lift up to the bump stops due to the torque from the front brakes. During normal foot brake operation the rear brake torque on the trailing arm applies a counter torque to (mostly) prevent the rear lifting.

If there is air in the rear brake lines this will allow enough time for the rear suspension to lift up during initial braking before the brakes kick in, and this can cause the suspension to be held too high whilst stationary after stopping.

Another possibility is that you've gone from 40 bar spheres (softer) at the rear to 30 bar ones. (stiffer) This problem tends to occur a lot more when the suspension is softer. You can check this by looking at the stamped number near the filler plug.

The 1.9TD was always supposed to be fitted with 30 bar rear spheres, but before 1996 the 1.9D came with 40 bar spheres, and I've known them to be mixed up before...

Regards,
Simon

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steviewonder7
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Joined: 08 May 2005, 01:02

Xantia rear end dropping cured.

Post by steviewonder7 » 17 Jan 2006, 20:33

Thanks for your reply Simon and appologies for not making it clearer what the fault was.I'll try and give a clearer version here:-
Imagine driving along at approx 30 mph and your approaching a set of traffic lights(these are lit up red) so you begin applying slight pressure on the brake pedal to slow you down and then you slowly come to a halt at the said traffic lights.Now,you're stationary,give it a second or two and the rear end of the car begins to raise itself back to normal height.This happened anywhere that required me to come to a halt.It's almost like ...while you're driving the car the car's rear end (body) has dropped a couple of inches and when you've come to a halt the rear raises back to where it should be.
Hope that make more sense???
Steve :)

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Mandrake
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Xantia rear end dropping cured.

Post by Mandrake » 17 Jan 2006, 21:47

Hi Steve,

What you really need to do is establish what is happening to the rear height while you're driving, by either looking in the rear view mirror as you brake (being careful to note what is in front of you :) ) or perhaps by getting someone else to drive the car for you and looking backwards, maybe even sitting in the rear seat.

Until then its hard to say for sure whats happening. It *sounds* like whats happening is that when you brake the rear is lifting, (without you noticing) due to poor rear brakes, and if this happens for at least 5 seconds the height corrector will let some fluid out, to compensate.

After you come to a stop, the body of the car, no longer under dynamic conditions, will drop and will now be too low. After a few seconds the height corrector will correct the height back up again.

Because whether the height at the back goes up or down during braking depends on the front/rear brake balance, if the rear brakes are working "too well" and the front brakes are not working well enough, you can end up with the rear actually being compressed by the brakes, rather than lifting.

On the other hand good front brakes and poor rear brakes has the opposite effect - the back lifts.

Then you have the height corrector to contend with - any error in height lasting more than 5 seconds will provoke a response from the height corrector trying to correct the "error" which will seemingly reverse the stationary stance of the car.

(EG if it was too high during braking the height corrector lets some fluid out, now the height is too low after you finish braking then it has to lift it up again)

I would suggest being a passenger in your own car and observing the stance of the rear suspension during driving and braking and see if you can notice what is happening while a driver tries gentle, moderate, and hard braking.

If you notice the back lifting up a lot during braking I think you have found your problem, and your rear brakes need attending to. (Bleeding and checking pad/disc surfaces)

Because the rear brakes don't work very hard in normal around town driving they can sometimes get surface rust, also people sometimes put in pads that are too hard and therefore not very sensitive, and the rear brakes due to their light loading can sometimes benefit from being fitted with one grade softer pads than the front brakes to keep them operating well.

If its doing the opposite and the back is going down during braking your front brakes may need attending to...

Regards,
Simon