XM rear jumps up

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nino
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XM rear jumps up

Post by nino »

The XM V6 saga continues...
after replacing the flat acumulator sphere at my local garage i seem to have a new problem. Before the acc sphere went bust the rear would drop after holding the brake for about 8 sec. After the replacement of the sphere (fine steering, no droping) i get the oposite effect. After about 10 sec of brake usage the rear end rises in a second.
pete_wood_uk
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Post by pete_wood_uk »

Forgive me if I've misunderstood, but is this after you've come to a halt, and are holding your foot on the brakes? Citroens can do all sorts of strange things in that situation - the wheelbase varies slightly as the car goes up and down (due to the trailing arms) so if you come to a halt and keep your foot on the brakes hard enough to keep the wheels locked, then the car can't rise up or down because it can't vary its wheelbase. Eventually, you ease your foot, and ping! This is normal behaviour...
This may not be your problem of course.
Best regards
Pete
nino
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Post by nino »

Yes, sorry for not being more precise. It happens while idling. After some 8-10 sec it just rises and stays that way for a while.
It also corrects itself if a travel forward a bit (not sure how much since it smoothly re-levels). Breaking to a stop seems fine.
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Post by Peter.N. »

Could be that you have a sticking rear height corrector, several applications of WD40 over a few days should do it, but as Pete says, if you sit with your foot on the brake you are holding the suspension in position and it will move when you release it. otherwise I wouldn't worry about it as long as it rides at the correct height.
nino
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Post by nino »

My mechanic mentioned the break cylinder when the rear was dropping. (leaking presumably)
Could it be a different sympthom of the same problem somehow, or will i be faced with the rear going down again assuming i get the height corrector greased.
jeremy
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Post by jeremy »

Just as an observation the brake valve (doseur) gets blamed for all sorts of problems and is seldom at fault.
If the valve were leaking I would expect the back to go down. The only way the back could rise would be if the front circuit were leaking into the back one which could happen via the doseur but I would have thought unlikely.
How old is this car, has it a version of hydractive? - if so which one?
Are you sure its the back going up and not the front going down? have you done Citroebics recently to get any air out of the system?
Jeremy
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Post by nino »

By citreobics you mean rising and lowering the ride height?
Like i said the read droped before the acc sphere was replaced, now it reises, presumably if the brake valve was faulty it still is. I'm wondering if this is a new unrelated problem.
It's a '91 V6 auto
8 spheres - hydra 1 i presume
tnx.
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Post by jeremy »

Yes thats Citroebics - raise and lower the car several times to get any gas out of the system.
Jeremy
William
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Post by William »

My XM jumps up suddenly when it's back at the normal ride height after citaerobics.
Could be disasterous if it happened while in motion but I've been assured it won't.
waynedl
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Post by waynedl »

Mine does same thing, done it about 4 times in 3 months and 5000 miles of drivin'. I think when it's done it it's been after citrobatics so that could be related. mines had new spheres everywhere except accu which has been tested as new.
It's not losin' any hydraulic fluid but when it goes up it goes sooo fast I think it's gonna flip over [:D]
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Mandrake
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by waynedl</i>

Mine does same thing, done it about 4 times in 3 months and 5000 miles of drivin'. I think when it's done it it's been after citrobatics so that could be related. mines had new spheres everywhere except accu which has been tested as new.
It's not losin' any hydraulic fluid but when it goes up it goes sooo fast I think it's gonna flip over [:D]
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Is it a hydractive model ? If so, its "normal" for it to occasionally jump in the air like that when going from full height down to normal height. My HA2 Xantia does the same sometimes.
All thats happening is that when its at full height the centre spheres have full regulator pressure applied to them, so there is not enough pressure differential on the hydractive control plunger to allow it to stay in the "soft" mode.
(It relies on the pressure supply from the main regulator being higher than the pressure in the hydractive centre sphere to push the plunger)
When the suspension is lowered to normal height there is still full pressure trapped in the centre sphere until a small amount of leakage allows the plunger to move far enough to start opening the valve to the centre sphere then suddenly WOOSH! and the valve snaps open and the pressure is equalized.
More of a design mis-feature than a fault, although I suspect that any stickiness in the operation of the slide valve increases the required pressure differential to operate the valve reliably and thus makes it more likely to happen.
Regards,
Simon
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