Need Help!, '92 V6 injection signal

This isn't all my own show and I'm perfectly happy for listers more qualified and directly
experienced in this aspect of McStrut Citroens to give chapter and verse on this. I am fully
aware (only too painfully) of the rubber tearing on the crown as much as rust issues on the
mounting plate!

I've personally found it IS indeed rare for the rubber to perish (in the UK at least!!) but only
too easy for rust to finish off the the strut mounting; accepted more so on a Xantia than an
Xm. In the instance of this original thread a Xantia strut head appears to have been fitted to
an Xm which I personally don't believe is such a great idea and why I'm at pains to bring this
design weakness/defect to everyone's attention!

If folk throw away perfectly useable strut tops I just wish I ran the company that makes
new ones! At the end of the day, it's their call - all I've tried to do is raise awareness of
this problem that won't go away anytime soon...

Andrew

This post has been edited by Andmcit on June 30, 2008 08:31 pm

Hi Andrew,

I notice in your thread to FrenchCarForum that Anders warned of the dangers of a strut top letting go at speed.

I also see that yours let go in the car park. As Max Miller used to say, now there's a funny thing; I've never heard of a strut failure at speed, they all seem to happen during slow speed manoevring or when parked.

I wonder if failure is instigated by large steering angles? We do know that the strut takes up some very funny positions as you go from lock to lock. I also wonder if it will be worth while knocking up a simple retaining strap for each leg. I visualise a top hat section made from, say, 3/16" (10mm) thick steel, bolted to the existing leg studs and fitting over the crown of the leg. It won't stop a faulty leg from failing but it may save the bonnet.

Derek

Hi Andrew

Sorry if my poor choice of words caused offence, was not meant personally. Have been away a couple of days while delivering a car with two V6's to the far north west of Wales before the tax ran out. Just picked up on this and dashed off a holding reply, will now try to give it a bit more meat.

Hi All

With Xantia strut heads there are three separate causes/risks of failure. XM's are fortunate in only suffering from two of these problems. I will attempt to describe the mechanics of each failure mode and the method of examination. Being fairly inept with computers I will start using words and try to add photos/diagrams later.


1-Axial Rubber Tearing

This can happen to both Xantia and XM Strut Heads and can occur even where no rusting is present. The main working component of the strut head is a large almost mushroom shaped block of cast rubber (part A ). If you imagine the strut rod as the stalk of the mushroom, this rod actually continues through the mushroom head. There is a very large thick circular metal ring (part B ) that sits on the outer half of the mushroom head. This metal ring has horizontal projecting ears that bolt the strut head to the car chassis. The rubber mushroom lets the strut rod twist and rotate slightly. These movement rates and limits need to be very accurately controlled to get the very precise steering geometry correct and consistent. It is perhaps for this reason that Citroen specified the rubber composition and designed the two deep quarter circle grooves in the underside of the rubber mushroom. These quarter circle grooves are almost vertically below the inside circle (central hole of part B ) in the mounting steel ring. If the rubber mushroom is overstressed the rubber tears at the points of maximum loading and this is at the ends of the quarter circle grooves. All four ends will eventually tear forming a full circle. The tears will then progress upward until a virtually free narrow tapering cone of rubber is just waiting to be forced up through the hole in the centre of the mounting ring.

Examination

This fault can only be checked for by detailed examination of the rubber of the underside of the strut head. Any tearing that has reached the top of the rubber mushroom is covered by a thin fixed metal skirt and anyway by the time the tear has reached the top of the mushroom the risk is high of one big bump poping the strut through. In examining the underside of the strut you need to look specifically at the ends of the quarter circle grooves for tears continuing the ends of the grooves towards forming a full circle. To get a complete examination you may need to pull down the rubber bellows covering the strut rod. If you find this cracking REPLACE the strut head as quickly as you can even if the rest if it looks pristine.


2 - Rusting of the Top of the Strut Head Mount

This problem can also happen both Xantia and XM strut heads. The outer top edge of the mushroom is a layer of rubber extending as very thin flaps over the top of the mounting steel ring (part B ). This rubber is (when new) bonded to the top of the mounting steel ring. Unfortunately for possibly various reasons this flap of rubber tends to debond from the bottom edge and bubble/crack due to rust under the bond.
This is initially no more than cosmetic surface rusting of a fairly thick structural steel section. Because it bubbles and cracks the rubber the appearance can be quite horrific when first spotted. All that actually matters is the residual thickness of the structural steel. Unfortunately this is both quite difficult to determine and the cracked/debonded rubber actually sucks water in by capillary action which accelerates the rusting process. If the rusting is allowed to continue then eventually the metal will thin and the central hole enlarge. This will put progressively more load on the quarter circle lands of the rubber mushroom until it tears into a circle and fails in exactly the same manner as Failure 1.

Examination

The rubber flap on the top of the strut head can easily be examined on the car for bubbling and cracking. The extent gives a fairly clear indication of the progress of any surface cracking but will not tell you very much about the actual condition of the steel strut mount. Carefully removing the loose and debonded parts of the rubber flap will both retard the rate of corrosion and expose the structural steel for examination. It may even stop the corrosion, on some of my strut heads it has allowed rust treatment of the steel. It is not possible here to give a visual guide on steel assessment but it may be that one of our club members has experience of ultrasonic steel thickness measurement. There have been some suggestions that Mk 2 XM strut heads were redesigned to reduce this risk. I have found no evidence in the two strut heads I have compared and think we are just seeing the start of the Mk2 struts rusting through. This form of strut head failure is at the end of a long and slow process with clear visible signs on the way so should not catch anyone out once they know what to look for.


3 - Rusting of the Underside of the Strut Head Mount

Added for completeness as this is an Xantia only problem.

Not satisfied with their success in the design of the XM strut head Citroen decided to repeat the design on the Xantia strut head with a little extra twist. Having found rust causing non structural rubber flaps they added an extra one to the underside of the strut top mount as well as on top of it. No only does this extra flap also debond and suck in moisture but for part of the year because it is in the wheel arch the moisture there is also salt water spray sloshing about in some considerable amounts and under a fair pressure. This causes accelerated rusting of the underside of the strut top mount particularly affecting the change of section where the ring of steel joins the edge of the rubber mushroom. The forging to make this change of section weakens the steel encouraging rusting at this point. So the failure this time is sudden with the steel strut top mount splitting into two parts, half on the chassis and half on the strut top mounts.


Cure

Do not buy, ride in or drive near Xantias. For once the Germans have it right!!!

Regards

XMexc

This post has been edited by xmexclusive on June 30, 2008 10:57 pm

I am trying to bargain a Part ex on an L reg Black Xantia a friend here on location has. Its just to knock 200k and she keeps saying Ill get rid soon... mind you, it is too good even after 200k to sell the bonnet off...

Have to admit, not many black ones about thinking about it, and if there is, they are good... I'll keep eyes open for you..

rgds
paul

So, a big fan of Xantias then, xmexec?

I'd think one of the issues with the collar mount apart from the rubberised covering that
traps in the rust is the penny pinching in the actual thickness of the weight bearing plate
even when new. Had it been manufactured in the days of the Cx, first the car wouldn't have
had a rubbish McStrut, and furthermore, it would have had a very generously built in factor
of safety or as I like to affectionately call it; brick outshouse engineering!! Big chunky metal
everywhere that would dent concrete if dropped on the floor!!

Don't make'em like they used to!

Andrew

I also note that I had one impending fail on my first XM that I was lucky enough to spot before it became a real failure, which would also be a shear failure of the rubber dome. The central sphere mounting was actually rising into the engine bay space, leaving the rubber and the metal dome cover in situ.

Was noticeable by the silver ring that appeared above the metal dome part. There was a clonking when cornering hard with that wheel unloaded, and given it was drivers side, was quite likely down to speed hump hurdling

Had the indy replace them both, but didn't see the state of the rubber at the time as it was a quick in-fit-away job as I neded to get somewhere. KNowing the issue in more detail these days, I'd definately want to keep it to examine more closely.

Remember that german XM V6 some time back that had been rolled - any a strut was through the bonnet....? maybe that was a failure one the move.... and it's just that we've not seen/heard of one within the group, so far.

regards
Dave

PS maybe we should spin these posts off into a seperate thread, as we seem to have stolen an engine/injection related thread.....

Hi All

I note Dave's comment on theme hijack and will try to move a copy into a self help when I add the diagrams.

On Andrews point about metal strength the fact is that the XM baseplate is actually quite substantial and even over engineered for its function when new. What is very surprising is the rapid structural deterioration in service of the complete component. That the Xantia one deteriorates at an even faster rate and from the underside as well helps by confirming that failure of bonding of the thin rubber is the key corrosion initiator. I am reasonably certain that I recognise the failure method as being Mill Scale Peel. Mill Scale is where a rolled steel or forged steel component gets oxides or impurities rolled or pressed as very thin layers into the finished surface. Immediately after manufacture it is very difficult to remove from the product surface. If left for some time rusting peels it off in large patches taking any surface treatment with it. During the peeling process the flakes on the surface suck any moisture under them accelerating the rusting of the underlying metal. If only they had galvanised the forgings or used stainless steel we would only be worrying about the risk of Axial rubber tearing on strut heads.

I would not now install new XM strut heads without removing the rubber top flaps and rust treating all the exposed metal. I also think there is actually a method of repairing axial rubber tearing and have kept a failed strut head to try this with.
To put things in context to date (10 years XM ownership, a dozen cars many still kept) I have been fortunate in not having a strut head actually fail on any of the cars and have been able to rust treat and save all those damaged ones without needing to remove or change a strut head. I have recorded the condition of strut heads on a number of other XM's and collected a few failures and of course some spares. I have concluded that there is no service age or mileage guide that will predict strut head failure. Mill scale extent is variable with each individual pressing as is it positions on the metal piece. Moisture conditions under the bonnet are very variable being most likely when the car is cold and parked outside. So I suspect a car garaged from day one may have a very long rust free strut head life. On axial rubber tearing I think that running with near flat front wheel spheres may cause the initial rubber tearing and once started this will continue more particularly with the heavier engined cars and sphere replacement/recharging will just slow the rate of tearing not save the strut head.

Regards

XMexc

This post has been edited by xmexclusive on July 01, 2008 11:09 am

There was a Xantia at my Indies a while ago which had double strut top failure. It happened during an emergency brake in a driving lesson. I presume it was not at great speed as driving lessons never are, but it would probably have been at more than manoeuvring speeds.

In this case both sides let go at once and so the effect on stability of the car would at least have been fairly even. If one had been in better condition than the other and only one had gone then I would have thought it would have pulled the car one way or other fairly hard.

Hi Rowan

That is interesting, did you get a chance to look or take a photo of the detail of the failed strut?

Regards

XMexc

Nope, I didn't get much of a look at the detail or any photos of the detail. I had a quick look and I think it was rust and not rubber failure. I just got a quick shot of the car as I was driving away.

Here are some pics of '95 Xm 2.0 Turbo with Xantia strut tops



You're ganna have to drill because positions of bolts are different.





Adapter - hub ring like a wheel spacer, approx. 4cm thickness.

I'm not saying that it would work perfectly.
All I want is just to give you guys an alternative which has been done for many XMs here.

If you can afford genuine XM strut tops, well it would be certainly better for your car.