Xantia strut wear, proof ?

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Mandrake
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Xantia strut wear, proof ?

Post by Mandrake »

Hi All,

Those of you that have followed my posts for the last few months will know of my attempts to track down harsh ride problems on my HA2 Xantia, which is also somewhat intermitant and also very sensitive to ride height. (The ride is very harsh and fidgety at normal height but a lot better 10mm higher than normal but still not what it should be)

I've already pretty much determined that wear of the strut shaft/bushes must be the problem, (especially given that lubricating them makes such a big, albeit short lived improvement, and other possibilities like spheres and balljoints have been eliminated) and today I decided to take some pictures of the shaft as I had noticed the surface didn't look too good.

With the magnification of a good quality digital image I can see what looks to me like pitting/scouring of the surface of the shaft where it seems to have worn through the hardening in some areas and I wanted some opinions on these pictures: (note, somewhat large filesize)

http://homepages.igrin.co.nz/simon/imag ... strut1.jpg

http://homepages.igrin.co.nz/simon/imag ... strut2.jpg

http://homepages.igrin.co.nz/simon/imag ... strut3.jpg

You may need to click on the expand image icon if you use IE6 as otherwise it will shrink it to the size of the window...

The first and third pictures in particular I think are quite revealing. The line up the middle is the reflection from the camera flash and at the bottom it is relatively smooth and you can even see a mirror image of the wheel arch to the right hand side, but further up the surface becomes very rough and diffuse.

The picture was obviously taken at full suspension height and the wear mark begins approximately at the position where the shaft would be touching the top bronze bush at normal ride height. Also the wear marks do not go right around the shaft, but appear only on certain rotational angles of the shaft. (Mainly in the 4 primary directions - forwards, backwards and sideways, where most thrust would occur)

Comments anyone ? (Especially anyone who has worked on the struts before and/or replaced/reconditioned any)

I should also point out that when I first looked at the car before buying it that the strut top rubbers were distorted (cracked and sheared) such that the gaters could not clip onto them, thus the gaters were both down and probably had been for some time (a year or more ?) before that so that in hindsight, water entry/damage of the shaft is highly likely. The strut tops were replaced just before I bought the car, however they didn't replace the strut cylinders....

Regards,
Simon
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Post by xantia_v6 »

I am no metallurgist, but a couple of questions arise when I look at the photos:

I think that the pistons are chrome plated rather than hardened in the classical sense?

It may be an artifact of the flash, but I am surprised to see the small but prominant horizontal markings on the pistons?

Is the wear due to contact with the bushes? I would expect that they would be designed such that an oil film prevents metal to metal contact under normal circumstances.

Could the wear be due to the rubbing of the oil seal, rather than the bushes (in the same way that on a crankshaft, the oil seals often wear a deep groove, even though the main journals are unworn)?

If the pistons have worn this much, if the wear is due to contact with the bushes, would expect there to be much more wear in the bushes, I would think that it should be measurable.

Do you think that this wear may be a result of prolonged running with the wrong hydraulic fluid in the system?
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Post by Mandrake »

xantia_v6 wrote:I am no metallurgist, but a couple of questions arise when I look at the photos:

I think that the pistons are chrome plated rather than hardened in the classical sense?
You could be right about that... I'm no metallurgist either... but usually the surface of a precision finished shaft like that is "special" in some way to be hard wearing and low friction, whether it be hardened or plated etc...perhaps if its plated the dull areas are where the plating has worn through ?
It may be an artifact of the flash, but I am surprised to see the small but prominant horizontal markings on the pistons?
You mean right near the top of the first picture ? Yes it looks like that to me too. It is an artifact of the flash in the sense that the flash exagerates the surface contour along the centre line of the flash, but it is showing up something which is real nevertheless. Hence my description of the shaft being "pitted". Most likely those little horizontal marks exist all across the dull area, but are only shown up by the flash along the central line where the flash reflection is at the right angle.
Is the wear due to contact with the bushes? I would expect that they would be designed such that an oil film prevents metal to metal contact under normal circumstances.
Surprisingly the struts seem to be designed so that the topmost bush just below the top of the strut (a bronze bush of some kind I assume) runs dry... something which I feel is a big mistake. The bottom bush(es) and piston are lubricated by the low pressure leakage however.

My guess is that the wear occurs between the shaft and the top bush (based on the position of the wear relative to the suspension travel) and has possibly been accelerated by water getting in. No doubt the bush itself is worn too.
Could the wear be due to the rubbing of the oil seal, rather than the bushes (in the same way that on a crankshaft, the oil seals often wear a deep groove, even though the main journals are unworn)?
Don't know about that one. I havn't been able to find enough information about the internal construction of the strut yet, the nearest I have is a drawing of an XM strut, and naturally although it shows a seal theres no way of telling what it is... the ease of getting oil/grease past that seal when lubing the strut suggests that its not a particularly good seal though.
If the pistons have worn this much, if the wear is due to contact with the bushes, would expect there to be much more wear in the bushes, I would think that it should be measurable.
Well strictly speaking the shaft is not the piston, at the bottom of the shaft there is a small head screwed (or pressed?) onto the shaft which forms the hyraulic piston, but I know what you mean. As to measuring the wear in the bushes, as far as I know the Xantia struts unlike the BX ones cannot be dissassembled, at least not in a way that won't wreck them in the process. Having said that there does seem to be a pressed on cap at the top that could possibly be removed...

Have a look at the following diagram which is an XM strut which is as close as I can find, and while there are a number of detail differences it gives the general idea:

http://citroeny.cz/servis/xmser/predni_vzpery.gif

(If someone has the Xantia version of this diagram please let me know :) )
Do you think that this wear may be a result of prolonged running with the wrong hydraulic fluid in the system?
Yes that thought crossed my mind too - in fact this car came with red hydraulic fluid in it, most likely some kind of ATF, and when I changed it for LHM I noticed that there was a lot of black particulate in it, which makes me suspect it might have been Dexron III type fluid with "friction enhancers" in it, and that could lead to accelerated wear.

I've already had to give the front height corrector a strip down and clean as the damping valves in the height corrector were clogged with this grit, and no doubt the back height corrector will need doing too.

The needle valves in the hydractive control blocks also have leakage in the "on" mode that I need to investigate which could also be attributable to wear/grit in the tapered needle seat.

I think water damage is more likely for whats shown in the photos though, since the top bush runs dry the wrong oil shouldn't be able to damage that section of shaft although it may wear the bottom section. (Not visible)

Regards,
Simon
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Post by citronut »

i would think that it is from when the gaitor was not atached and the dust seal has become impregnated with dirt and grit,im also suprised with that much damage the strut is not leaking presurised fluid,because that part of the shaft must be running in and out of the presure seal
regards malcolm
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Post by jeremy »

Interesting. Myown experience is that good struts make a world of difference.

I wonder - probably too difficult to do on yours but quite easy on a BX - could you rotate the siding (piston?) 180 degrees by removing part of the top fitting and turning it? - so that an unworn part of the sliding piston is presented to the worn face of the bearings?

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Post by Mandrake »

citronut wrote:i would think that it is from when the gaitor was not atached and the dust seal has become impregnated with dirt and grit,im also suprised with that much damage the strut is not leaking presurised fluid,because that part of the shaft must be running in and out of the presure seal
regards malcolm
Hi Malcolm,

No sign of leakage whatsoever. In fact after lubricating the shaft with oil and/or grease only a few days later the shaft is completely dry to the touch again.

I don't think the wear marks I've photographed would reach the high pressure seal point at the bottom even with the suspension right down, but I could be wrong.

There is also no excessive leakage - the front suspension stays up without dropping at all for 8 hours, and over a couple of days it has only lost about an inch.

So do you agree that is a significant amount of surface damage that could affect the ride ? Or could the real problem be hidden inside the strut unit ?

Regards,
Simon
Last edited by Mandrake on 24 Dec 2005, 10:43, edited 1 time in total.
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Post by Mandrake »

jeremy wrote:Interesting. Myown experience is that good struts make a world of difference.
My own experience is the same too - a bit of lubrication of the struts makes a world of difference even when they're this badly worn (or perhaps BECAUSE they're this badly worn) and helps convince me that the struts are indeed the source of the problem, unfortunately the effect of the lubrication doesn't last, at least on my car.

On my Dad's car which from memory doesn't have any wear marks on the shafts (I only looked at them once) the one greasing session that I did on them several months ago is still lasting well. (It was doing the classic creaking and groaning before that)
I wonder - probably too difficult to do on yours but quite easy on a BX - could you rotate the siding (piston?) 180 degrees by removing part of the top fitting and turning it? - so that an unworn part of the sliding piston is presented to the worn face of the bearings?
Yes it could be turned around, it would just be a matter of loosening the nut at the top, breaking the taper, rotating it and tightening it again. (While depressurized and supported of course)

The main reason I havn't tried it is because the shafts will have already been rotated a random amount by the mechanic who replaced the strut tops just before I bought the car, as there is no identity on which way to face the shafts during reassembly.

Because of this and the seemingly heavy amount of wear I doubt that turning them will give any real benefit, and may actually make things worse depending on how the different wear areas line up...

Regards,
Simon
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Post by AndersDK »

Anyone with a decent knowledge on mechanics and cars can tell it's not right to have this surface running dry against anything else ...

Thats why I keep telling DIY owners to lubricate exactly this part of the strut. Nobody seems to believe it helps - other than the few owners who DID try it in fact.

The strut internals are designed to keep an oil film on protruding parts to prevent they eventually lock up.

Those of you with experience on the BX front struts knows that it is the felt washer inside the strut at the top slide bushing that keep the strut film intact.
Later investigations (i.e. from Tom) showed that the BX struts could be re-wetted on the felt washer from outside using the seeping method described some time ago.
Unfortunately this method does not work with Xant & XM struts because of a different internal design.

It is no different from any other hydarulic strut/ram cylinder found elsewhere in mechanic constructions.
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Hmm?

Post by neil123 »

Anders... ok, I believe you! Lubricate with what? How? How often?

Cheers

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Post by FrenchLeave »

Purely out of interest and of no use as an answer to your problem, the process used to deposit the hard chromium surface on aircraft oleos is called fescalizing. I would think Citroen use a similar or identical process.

I'm still puzzled by all this talk about lubricating the top bush. Looking at the exploded drawing of the XM strut, can someone please explain to me how the leakage LHM gets to the return pipe on the rubber bellows without passing through the top bush?
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Post by Mandrake »

AndersDK wrote:Anyone with a decent knowledge on mechanics and cars can tell it's not right to have this surface running dry against anything else ...
I agree entirely. And yet the Xantia struts seem to be designed without any specific or long term way of lubricating that top bush. They probably have a felt washer at the top too, but thats not enough IMHO.

At one point I considered (mainly as a thought experiment) the possibility of modifying the top bush to have an oil feed hole and groove in the middle of it fed by the leakage pipe. If the struts had something like this from new its possible they would hardly wear out at all and never have the creaking, groaning, and harsh ride problems they now get quite quickly with age. (Well under 10 years)
Thats why I keep telling DIY owners to lubricate exactly this part of the strut. Nobody seems to believe it helps - other than the few owners who DID try it in fact.

The strut internals are designed to keep an oil film on protruding parts to prevent they eventually lock up.

Those of you with experience on the BX front struts knows that it is the felt washer inside the strut at the top slide bushing that keep the strut film intact.
Later investigations (i.e. from Tom) showed that the BX struts could be re-wetted on the felt washer from outside using the seeping method described some time ago.
What is the "seeping method" ? Is this where the return pipe is dipped in a jar of LHM while raising/lowering the suspension ? Or simply applying oil to the shaft at the top and raising/lowering ? (Both of which I've tried before...)
Unfortunately this method does not work with Xant & XM struts because of a different internal design.
Do you know what is different about them that causes it not to work ? By what mechanism does a Xantia strut try to lubricate the top bush ? Because I can't see any....

Regards,
Simon
Last edited by Mandrake on 24 Dec 2005, 20:28, edited 1 time in total.
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Post by Mandrake »

FrenchLeave wrote:Purely out of interest and of no use as an answer to your problem, the process used to deposit the hard chromium surface on aircraft oleos is called fescalizing. I would think Citroen use a similar or identical process.
You could be right there. Would you agree that the non-shiny dull area in my photos is where the chromium surface has worn through to reveal rough bare steel ? And would this rough steel have a lot more friction than a smoothly polished chromium surface ? (Especially under dynamic loading conditions of side-thrust ?)
I'm still puzzled by all this talk about lubricating the top bush. Looking at the exploded drawing of the XM strut, can someone please explain to me how the leakage LHM gets to the return pipe on the rubber bellows without passing through the top bush?
There is no return pipe on the rubber bellows on a Xantia front strut - it's not designed like the rear suspension cylinders. You'll notice in the diagram of the XM strut that the collection point for the overflow pipe is right near the bottom, just below the rollbar droplink bracket. There is a small hole in the side of the strut here, and the overflow pipe has a small square fitting that clamps on to this with a steel band strap.

Due to gravity there is no way for the oil to travel up the shaft to the top bush - and the shaft doesn't move enough even over full suspension travel to wipe the oil up there...(or only barely, and rarely does the suspension travel fully down on an anti-sink model)

Regards,
Simon
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Post by Clogzz »

Mandrake wrote:If someone has the Xantia version of this diagram please let me know :)
Could this be part of it ?

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Post by Mandrake »

Hi,

That looks like a BX strut to me unfortunately. Also I already have an exploded assembly diagram like that for the Xantia struts, what I'm after is an internal diagram like the XM one...

Regards,
Simon
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Post by Peter Mannn »

From a background as an hydraulic engineer, it is my opinion that the changes Peugeot instigated in the front suspension are inferior in both design and implementation. The original Citroen system (where the rod/piston is kept clean and lubricated by being sealed within a boot) is ideal.
Having exposed the rod in the fashion of a macpherson strut sets us up for problems down through the years.
In a top-quality industrial hydraulic actuator, this exposed rod is normal practice. However, the hard-chroming is laid onto a hardened rod, and then is honed to give a fine crosshatched surface (rather than the shiny finish one sees on cheap-and-nasty actuators). The crosshatching allows a film of oil to remain on the rod as it passes out through the pressure seal and the wiper seal. This oil film facilitates wiping the dust from the rod, and lubricates the wiper so that it does not chatter and bounce while the rod is being retracted (I suspect that it is the wiper that groans when the front sinks).
I made a simple modification to the front struts on my 1994 Xantia, which has done a tolerable job of keeping the struts lubricated ; what I did was to take a strip from the rolled/stitched end of an old towel, soak it in gearbox oil (which is less inclined to evaporate) and then fastened a ring of the oiled towel onto the external rod using a nylon cable tie. This is then pushed up beyond the range of stroke, where it remains, and from it a slow weeping of oil onto the rod helps to keep the wiper seal lubricated and working optimally.
This has been in place for a couple of years, and the suspension has remained reasonably quiet and smooth without further intervention. And at 130,000 km, there is no apparent degradation in the suspension.
And while I on the subject of maintenance innovations, I have found it worthwhile to make an injector device to put SAE 85-130 Limslip differential oil into the CV joints, the triax, and through the rubber boots that seal the suspension and steering knuckles.
This I made by taking a common spray bottle, removing the spray adjuster and drilling the spray orifice out to make an interference fit with the stem of a cotton bud. The stem can be flared (as in a plumbing fitting) by briefly passing the cut end through a flame, and the plain end inserted through the enlarged hole, so that the flared end prevents it being spat out under the pressure from the trigger pump. On the other end of the cotton bud stem, a small diameter flexible tube can be retained by interference fit. This tube can be sealed into the plastic end of a hypodermic needle (available in a re-inking kit for inkjet printers).
On mine, each stroke of the trigger pumps about 0.2cc. For the boots on the driveshaft, I remove the ring clamp and slide the needle between the boot and the shaft, to avoid making a hole (which might grow bigger), and then re-seal with a narrow hose clamp (making sure that it has no sharp edges that could chew into the boot). With the knuckles, I mark with paint on a flat surface, then inject through the centre of the mark (so I can find the hole again next time.

You may have noticed that after a number of years, the grease shrinks and goes stiff. This procedure replaces the oil that has evaporated and restores the lubricity and cushioning provided by the grease, and so significantly extends the working life of these critical components.
:D
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