Xantia strut wear, proof ?

[Mandrake]

Thanks for the very informative post Peter,

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.

I agree entirely. Having owned a GS for many years (which quite possibly has the closest to ideal suspension mechanical design of any Citroen) the McPherson strut is indeed a very poor substitute which has many failings in both geometry, operation, and reliability.

Not the least of which is excessive parasitic friction which is greatly increased during increased side thrust induced by cornering, braking, and accelerating - something which is a non issue with the seperate ram and pivoting parallel arms of the GS/CX.

They should never have combined the jobs of hydraulic piston with geometry supporting strut.

Unfortunately we are stuck with struts in the Xantia, so I'm trying to make the best of the situation....

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).

Interesting, I don't recall having seen a fine crosshatch on hydraulic rams before, maybe I just havn't seen the right kind. What prevents excessive leakage across the pressure seal with the crosshatch ? Or is it just an extremely fine one like a microturbine on a camshaft seal ?

Given your background would you say that my photos show serious damage to the chrome surface in some places on the shaft ? The ride characteristics are certainly those of excessive parasitic friction. (harshness, fidgeting, increased harshness and fidgeting during cornering etc)

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.

I thought about doing a similar thing myself by attaching a felt washer to the top of the strut cylinder housing and soaking it in oil (probably LHM), however I'm very wary of gearbox oil due to it's sticky nature.

I actually tried some gearbox oil on the shaft recently (possibly a bit too much) on the theory that because it was sticky it would cling to the shaft and last much longer than LHM, unfortunately I now regret it as it has definately made the ride considerably worse, presumably due to the extremely sticky nature of gearbox oil inhibiting free movement over small bumps, effectively increasing the low level parasitic friction even further. After removing as much as the gearbox oil as possible and relubricating with LHM it has improved again but is still worse than it was to begin with, so I wouldn't recommend anyone use a sticky oil like gearbox oil...engine oil might be ok but I havn't tried it.

I found that LHM gives the most improvement but is also the shortest lasting, better is Lithium L2 grease, not quite as much improvement as LHM but quite long lasting even without a resoviour, an no detrimental effect like the gearbox oil.

Unfortunately my struts seem to be at the point where the wear is simply too much for any amount of lubrication to fix, so I'll be replacing them soon, but I will definately be looking at ways of trying to lubricate the new ones effectively so they last...

Regards,
Simon

[Peter Mannn]

The crosshatching is very fine, much finer than in a cylinder liner. This was on servoactuators, which were engineered to minimize stiction (breakout friction) so as to optimize the ability to position the device or apply a force with the finest achievable precision. These actuators were extremely durable, in part because side loadings were sustained by a long bronze bearing, which kept the side bearing pressures relatively low. There was no appreciable leakage across the pressure seals unless the rod had been damaged.
In the suspension of a car, normal actuator friction is of much less significance, and what you report sounds more like mechanical binding or severe damping, rather than normal seal/bearing friction. As such, I think the differece in viscosity between LHM and gearbox oil is relatively trivial. I consider oil superior to grease (as others have used) because the soap content in grease may possibly taint the workings of the hydraulic system .. just playing it safe.
Yes, the surface on the worn part of the rod is less than lovely, but generally one might choose to leave that in place until an external leak became apparent, although the dents could draw some dust into the system and with the primitive filtration in the Citroen, dust would accelerate wear in the pump.
My own Xantia (which, alas, is not hydractive) gives a fairly firm, sporty ride with all components shipshape. It is only on larger and lower frequency road deformities that the loping gait of the Citroen is apparent. That is until one rides in a car of different lineage, when one is convincingly reminded that the Xantia ride is 2 to 3 times smoother. And of course, the faster you go, the better she rides.
Hooray for speed.

[Mandrake]

Hi Peter,

The crosshatching is very fine, much finer than in a cylinder liner. This was on servoactuators, which were engineered to minimize stiction (breakout friction) so as to optimize the ability to position the device or apply a force with the finest achievable precision. These actuators were extremely durable, in part because side loadings were sustained by a long bronze bearing, which kept the side bearing pressures relatively low. There was no appreciable leakage across the pressure seals unless the rod had been damaged.

Ah.... sounds like that would have worked better in the struts than what they did then. Because IMHO "breakout friction" or static friction as I call it, that has to be overcome before the suspension can move at all over a small movement is the number one reason for ride harshness (and a tendency to fidget over small bumps) in most cars.

Conventional coil sprung McPherson struts are among some of the worst in this regard because of the high mechanical friction of the shock absorber towers and the lack of arm leverage to help overcome that friction.

This is where older Citroen's with parallel arm geometry really shine - pivoting bearings instead of slide bears reduce the friction, the leverage of the arm (at least 3 to 1) helps overcome any static friction of the hydraulic ram, and the ram design itself all contribute towards extremely low static friction and I think that plays a major part in the "magic carpet" ride and stability that older models are reknowned for.

In the suspension of a car, normal actuator friction is of much less significance, and what you report sounds more like mechanical binding or severe damping, rather than normal seal/bearing friction.

I'm sure its a combination of high static friction and mechanical binding under thrust. A few months ago the first time I lubricated the strut with LHM I was simply amazed at how good the ride became - it really was the "magic carpet" ride you would expect of a Citroen, no harshness, no fidgeting, however it didn't last. What it did give me though, is a glimpse of what it COULD ride like if the struts were in perfect working order, and showed me just how important elimination of static friction and binding is to the ride.

As such, I think the differece in viscosity between LHM and gearbox oil is relatively trivial.

It's not the viscocity I think, but rather the stickyness of gearbox oil. There was no doubt it made the ride worse, I noticed it immediately when I went for a drive, and immediately regretted doing it.

I consider oil superior to grease (as others have used) because the soap content in grease may possibly taint the workings of the hydraulic system .. just playing it safe.

Soap content ? I don't believe there is any in Lithium L2 but I would have to check up on that. The reason why I used that grease in particular is that it is known to be compatible with the LHM and the seals used on Citroen hydraulic systems, and if a small amount of it finds its way into the system it won't do any harm, unlike some other greases. Much less likely to do harm than sticky gearbox oil.

Yes, the surface on the worn part of the rod is less than lovely, but
generally one might choose to leave that in place until an external leak became apparent, although the dents could draw some dust into the system and with the primitive filtration in the Citroen, dust would accelerate wear in the pump.

I'm not thinking about replacing it due to leakage (it's not leaking at all) but rather due to harsh ride problems.

My own Xantia (which, alas, is not hydractive) gives a fairly firm, sporty ride with all components shipshape. It is only on larger and lower frequency road deformities that the loping gait of the Citroen is apparent.

My Dad and Mum both have SX Xantia's without Hydractive 2 and I know what you mean - relatively firm ride as Citroen's go, but still a lot better than the average car. The Hydractive 2 (at least when the struts were well lubricated) is easily twice as smooth as the standard model.

I am curious, have you ever owned a DS, CX, or GS before to have a comparison of what a Citroen should ideally ride like ? (I've owned a GS and my Dad has owned both a GS and a CX, all sadly now off the road due to the ravages of time....)

That is until one rides in a car of different lineage, when one is convincingly reminded that the Xantia ride is 2 to 3 times smoother. And of course, the faster you go, the better she rides.
Hooray for speed.

Yes, I've noticed that the better a car rides, the more you take it for granted, the more fussy you become, and the more intolerant you are of any slight irregularity in the ride.

Then you hop into another "conventional" car and you come crashing back down to earth and realise just how good the Citroen is, even though you dont think its riding to the standard it should be

Regards,
Simon

[citronut]

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

that cant be a BX strut because it has the drop link mouting bracket,and BXs dont as there link rod ataches to the lower arm
regards malcolm

[AndersDK]

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

that cant be a BX strut because it has the drop link mouting bracket,and BXs dont as there link rod ataches to the lower arm
regards malcolm

Agree with Malcolm here. The bracket seen is the XM style. The Xantia struts have a simple vertical plate welded on.
Apart from that the XM & Xantia struts are the same design internally.
I have not yet browsed the PR-net for available info on Xantia & XM struts to see if any types are used acroos XM & Xantia models.

Since the BX was discontinued - it seems that every bit (well - almost) on later Citroens are model & series specific over the production years.
Which also fits the general impression of owners sometimes reporting very differently on driving experiences in (different series) of the same car.

[Peter Mannn]

Yes. I drove and maintained a 1974 D Special for 14 years. Of all my cars, this was the one I loved most. Yet, the suspension in this was much firmer than the 1972 DS21 with which I had a brief and expensive affair, and was not a lot more compliant than my Xantia. Although I lack the motive to find the Xantia's limits of adhesion cornering on a dry sealed road, I suspect that the D would acquit itself similarly, given comparable tyres. During our 14 years together, the limits of adhesion in the D became well known to me, and the much greater level of freedom back then allowed me to routinely work close to those limits as a matter of personal preference.
I also had a 1974 GS, which endeared itself to me through its valiant performance, comfort and economy. Only regret was lack of airconditioning.

Given your description and comments, I suspect mechanical binding where the wear in rod and top bearing match ; this would explain the improvement when running 10 mm higher. Not having seen a strut dismantled, cannot comment on whether a modification might serve better than straight replacement ... but anticipate that replacement would be more pragmatic.
No substitute for making it right in the first place. Entertaining a romantic hope that the C6 heralds a return to original values.
Somewhat baffled at how UK cars deteriorate so much faster than mine. At 128,000km, mine still drives and looks like new. Put in my first set of brake pads this year, and have just purchased the bearings for rear suspension ... although they failed only because they are absurdly small for the task ... this is the first mechanical failure so far, although I had a near miss with head gasket and heater matrix. Touch wood, she will continue to be kind to me.

[Peter Mannn]

PS: I agree with your comments about the lower friction in a pivot bearing. The older cars had the additional advantage of higher profile tyres and larger wheel diameter for absorbing chatter from small profile irregularities on road surface.