Front Top link bushes - thoughts on poly

[Kman1600]

Hi All,

Sorry but my nature just won’t let this lay, I am a Mechanical Engineer after all and kind of need to get answers to these sorts of questions.

I contacted the crash investigator for the accident in question and had a short but informative exchange regarding his findings; we engineers do tend to keep things as succinct as possible. Suffice to say that he made no direct link between this failure and the use of Polybushes, so you’ll have to draw your own conclusions regarding their suitability for use, but don’t quote this accident. He is completely satisfied that in this case the cause was excessive corrosion on this very hard to inspect but safety critical suspension component.

So I’ll reiterate my previous point. The real lesson here is one about properly inspecting our cars for dangerous levels of corrosion and “don’t judge a book by its cover” this car was very shiny, had had a lot of money spent on it, was MOT’ed etc…. As pointed out by a number of posters on this and other threads on the subject, this area is incredibly hard to inspect correctly, an MOT is unlikely to pick up the issue unless the MOTer really knows his P6’s. To be really sure of the condition you unfortunately need to remove the elbows and have them blasted, a bit time consuming but not terribly expensive when compared with the potential risks.

I hope that helps,

Tim

 

[pat180269]

I did a rear suspension rebuild over the winter and had the parts blasted. I was shocked with the condition of the O/S elbow after blasting, acid etch and zinc plate.

There were pin holes in an arc around the welded strengthening washer on the lower link and looking at pictures of those which have failed this would appear to be at the failure point. I might add that the elbow looked perfectly serviceable even when removed from the car and inspected . After processing, the metal on the outer edge was noticeably thinned by corrosion. I ended up strengthening them by making up plates as shown here :-

viewtopic.php?f=21&t=13354&hilit=gmr&start=30

I am certain the problem is one of corrosion; whether the polybushes expedite failure on a weakened part I don't know but it definitely isn't the root cause.

I have talked with Mark Gray in the past about the possibility of offering exchange elbows; where blasted and repaired elbows could be offered in exchange. The only sure thing is that the problem will not go away. I tried to buy good used elbows but decided there was no way of knowing how good they were until they had been processed in the same way as mine.

Many owners I have talked to seem happy to ignore the problem though.

 

[westOz74P6B]

Well done Tim, thats what was needed, to find out the outcomes from the actual crash investigation in which thourough analysis determines root cause, to calm down the worry over poly bushes but more importantly to share the findings so the suspension component in question can be highlighted as a case to be more vigilant when inspecting and as a warning to buyers, sellers and restorers alike. Worthy of a "sticky" thanks to Tim's findings. Maybe even worthy of instigating a separate topic on saftey issues/concerns of our P6's to highlight to other owners such as this subject and others such as engine fires caused by the ageing plastic fuel lines in our engine bays so they dont get lost in other topics?????????? Safety should always be kept to the fore. It would be a first for this forum to start such a topic in the Board index as, of the other vehicle forums I visit, none I've seen focus on safety as a stand alone topic.
Scott

 

[colnerov]

Hi, WHS ^^^ I agree that is a good idea.

Colin

 

[rockdemon]

Who feels suitably qualified to write the sticky then?

 

[sowen]

Quoting myself from this thread last year http://www.classicroverforum.net/viewtopic.php?f=22&t=17109 after I went to the effort of digging out a set of elbows which demonstrate how and where the elbows typically corrode. Feel free to use the photos.

I had a 1976 P6, bought as a spares car, which had been off the road since 1990, so roughly 14 years on the road. I've kept the elbows and had them blasted a few years ago.



In some of these pictures you can see the extent to which the rust has eaten into the metal inside, weakening the structure of the elbow, but on the outside they look perfectly good









The original metal appears to be approximately 2mm thick and not particularly substantial in design, and I estimate it has been eroded at least a third of that in places on the inner surface.

What I'm saying is they may look alright on the outside, but going by my pair here they look like they rust from the inside out.

 

[westOz74P6B]

Yes Simon, the thread you refer to is worthy of referencing to in a safety section in its entirity,

Rockdemon wrote;

Who feels suitably qualified to write the sticky then?

Methinks a qualified Mechanical Engineer :wink:


I would, though, suggest a 'Safety Matters' section be put in between the 'non technical' and 'P6' section, with a descriptor along the lines of,
"Safety related issues concerning the P6 and P6B for the awareness of forum members and guest viewers"
and then move topic viewtopic.php?f=22&t=17109 across in its entirity and maybe this thread as well????
and there was an issue/topic Ron (sydneyrover) had about the original plastic fuel lines splitting in the RV8 engine bay, the reserve tap 'O' ring etc, to name a few safety issues

Is this sounding plausable Rich/Tim/Colin/Simon without being too alarmist??

There wasn't any info Tim on the exact point of failure from your contact, was there? rather than a general corrosion being the cause.

Scott

 

[Kman1600]

Hi,

I have no further details beyond corrosion being the primary cause, post a failure like this it is unlikely that you’ll pin point an initial point of failure. It is probable that some momentary high stress situation tipped the weakened part over the edge, striking a pot hole, suddenly braking or swerving etc…. For a number of people on here the final failure has occurred at low speeds but probably still when stopping suddenly or turning tightly etc…. Having this failure occur at low speed is at least part down to luck and we really shouldn't be relying on any level of luck.

I’m very OK with a safety section but a little wary of copying large rambling threads over into it; I think the seriousness of the issues can be lost within a multi-post thread.

In response to this specific issue everyone of us should be under our cars giving this area a thorough examination, better still taking the steps of removing, blasting, examining, repairing, repainting etc… this safety critical, know catastrophic, failure point. To not do so is quite frankly reckless. As illustrated by the overall condition of Chris’s car, and others that have similar failures, this issue can affect absolutely any P6 regardless of Mileage, MOT status, perceived condition. If you haven’t checked it assume the worst, those that have check have often been horrified by what they have found.

First and foremost our cars must be safe, so before you spend your time, money and effort making it pretty, make sure is solid where it counts.

Tim