Citroen XM Forum

You could argue the early tops shouldn't be used at all.

That is a bit alarming Russ as I have this type on all but one of my cars! Nevertheless all but one set are original and do not appear about to fail. With regards, Matthew T.

I don't think they fail without warning. What happens is the dimples fail to provide sufficient grip and start to rattle in the upper housing.

iirc, Dean had a later type failing, which rattled and allowed the upper section to move vertically when the wheel was raised off the floor.

MTXM wrote:

You could argue the early tops shouldn't be used at all.

That is a bit alarming Russ as I have this type on all but one of my cars! Nevertheless all but one set are original and do not appear about to fail. With regards, Matthew T.

An extreme reaction I admit. But if Citroen updated them in such a way, it does point towards them not being 100% fit for purpose.... Fault in that argument is your have lasted all this time!

I thought this and the strut type restrictions were common knowledge.
I guess it may be some years ago that I wrote the details up.
Perhaps it was on the old forum.
If you change early heads for later Mk1 thin rod heads Citroen mandate changing the struts as well.
The position of sealing rings and oilways were altered.
New type heads and old type rods were the combination that interfered with oil flow.

Adding security bolts is an option but the bolt position is above the rain shield so will be visible.
I guess four bolts placed between the four dimples would be ideal.
Drilling the cast metal could be difficult and risk introducing cracks in the grain structure.

Very important not to run four dimple heads with flat spheres or suspension on high.

As I understand the problem started very early on first with V6's.
I do not believe there was a general recall but some FOC repairs.

The failure mode is the same as axial tearing of the rubber cone.
Even more difficult to examine for and predict though.
Having recently suffered axial tearing at 20 mph on a straight road it is not an experience I would recommend.

John

That is very helpful advice as ever John and I think I shall have a particularly careful look over my cars!! With regards, Matthew T.

Yikes! that's alarming having a strut top go whilst driving. They tend to wait and surprise you over night!

The strut head failure that causes the rattling noise is not the dimple failure.
This is caused by the top of the rubber cone delaminating from the underside of the steel baseplate cone.
This is the least serious mode of strut head failure.
The rubber cone remains fully intact and just bounces gently under the steel cone as the load comes off that strut.
It makes a rattling noise because there is usually a thin layer of rusted steel still stuck to the top of the rubber cone.
I believe the original cause to be using poor manufacturing methods in forming the steel baseplate.
Had two XM's with this mode of failure over the years.
Each time both strut heads were similarly affected.
That tends to confirm manufacturing rather than service degradation as the root cause.

I do not think dimple failure will give any warning at all.
The contact projection into the ring slot is less than 1mm.
The length of contact is around 3 to 4 mm top and bottom only.
Only four of these contact points to resist pull out.
So I estimate it is held together with a steel contact area smaller than 4 finger nail clippings.

John

That is alarming. That little?

I think I'll do a strut top info page at some point and that way all the important info regarding them will be in one place and easy to find. I might need your help with this John if you don't mind.

The contact point may be small, but it creates an interference fit, whereby the lower tube, with dimples, is larger than the upper tube. I can only see two ways this could be overcome; 1. the front spheres are flat and large forces are being transmitted to the joint, 2. there is wear over time and eventually the dimples wear enough of the casting away to be able to slip through.

It's worth considering that as the two parts corrode, they make the intereference fit even tighter.

I don't think a car fitted with these is in danger as long as the spheres are not allowed to go flat.

Interesting. Will bear this in mind when putting all the strut top info together.