Russ's 2.1 SED Auto now in Mandarin

[Dieselman]

A third point worth considering is that the failures were in very early production versions of this type of strut top. Rather thant he number of dimples being the issue, I suspect it was just a manufacturing tollerance defect, with thenumber of dimples being increased as a safeguard, but not a necessity.

[russ92xmsed]

Do we know when they changed to 10 dimple? 1990?
John has mentioned the early tops tended to fail on V6's too. Wonder if that's down to weight, or other stresses.

[Dieselman]

I believe the change was RP5439, September '91.

V6 will impart greater stress due to using spheres with lower gas pressure and smaller damper orifaces, coupled with the heavier engine, though I'm not convinced that would cause a greater failure rate of the strut tops.

My understanding was it was only very early stut tops that failed in this fashion, hence I suspect a manufacturing fault.

[russ92xmsed]

That's very useful information. Surprisingly later than I thought.
I will make a note of that and include it in the strut info. It's good for owners to understand which strut tops they have, if it comes to replacing them.

[xmexclusive]

The Citroen Technical Bulletins never mention the change from 4 dimple to 10 dimple so the change date is unknown.
I have never seen a 10 dimple straight sided (original) strut head or a 4 dimple step sided (later) strut head.
So the date suggested above is in all probability correct.
The more recent designs of strut head I have examined (Xantia & C5) are of similar construction.
They all use 10 dimples on the heads.
It would be interesting to know about the earlier BX ones.

In my posts I have tried to define each mode of failure, risk when it happens and preventive measures.
There is a wide range of modes, risks and measures.

Here is my assessment from low risk to high risk.

Rubber cone peeling from baseplate will typically run to next MOT and be spotted on the shaker rig.
Cone rusting would pop the bonnet but is a slow process and easy to inspect and spot.
Axial tearing will pop the bonnet, grows with increasing rapidity and is quite difficult to inspect for.
Top head separation will pop the bonnet even with protection rings in the rubber and cannot be inspected for.

Some years ago the NZ MOT raised serious concerns about the safety of the Citroen strut head as a component.

The actual failure rate of each variation may be low but the results of individual incidents could be very serious.

As far as I know there is no factual evidence that strut heads usually fail while the car is parked up.
So until we obtain and can quote that evidence we could be repeating myth or unsubstantiated opinion.

With 4 dimple heads I am of the opinion that they are best avoided if possible because of the risk on failure.

The recent experience of axial tearing is still being evaluated.
There is no way of knowing the prior history of a pre-owned strut head, it may have run long on flat spheres but show no outward signs.
Strut head rebuild with protection rings is most likely for all mine.
Elastomer rather than rubber as strength rather than appearance suits my use of XM's.

John

[russ92xmsed]

That's great John, thanks. I can use all this on the diagrams I'm putting together.

I have always been intrigued as to why BX's don't seem to suffer from strut issues. No one ever talks about them. Maybe it's because they are lighter cars and suffer less stresses.

[xmexclusive]

Hi Russ

Citroen have run into service trouble with most of their rubber based strut heads.
They fall broadly into two groups, standard and ultra compact.
All the ultra compact designs of strut heads (XM and C6) have suffered some early service failures.
As Dieselman suggests these failures are virtually certain to be due to manufacturing issues.
The limited design options to fit the available space will have been a key factor generating this situation.
For both these models that reduced space was predetermined by car body shape.
For those cars with the earlier design of full size strut heads it is always long term component degradation that causes failure.
A good example of this is the excessively rust prone Xantia strut head baseplate.
Here a simple design change added to prevent rusting proved to do the opposite later in service life.

If anyone wants to donate a scrap BX strut head I would be pleased to investigate one.
Same with service life reports as any such information would be useful.

John

[White Exec]

John, Russ

I think there were very few reports of BX strut tops giving out.
Some folk here (? xantia_v6, Gabor . . .) might know more.
BX hpn system was the last of the "long-travel" wheel movement Citroens, which must have helped, along with having no Firm mode (unless it was a GTi!).

Found this just now. Contains a cross-sectional drawing of a BX front strut.
http://www.imim.pl/files/archiwum/Vol1_2016/17.pdf
A 2016 paper!

C.

[xmexclusive]

Hi Chris

Thank you for finding and posting.
That BX strut head cross-section tells all.
The design change for the XM reduced the rubber contact area by a dramatic amount.
The Xantia despite available space had a similar reduced rubber contact area.
The C5 got steel plate angular reinforcement built into the rubber.
Anyone got a C6 strut head cross-section diagram?

John

[russ92xmsed]

That is interesting. The BX strut is quite different.

It does seem quite counterintuitive to reduce the rubber contact and design a suspension system with less travel. It almost, to me at least, seems obvious these early failures were going to happen.
The result of wanting a less body roll it appears.