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CSR owners check your rear suspension mounts


Gareth H

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As some know I suffered a lower rear damper mount failure to my CSR on the F & C run, fortunately it failed on a 50mph dual carriageway as opposed to some of the faster twisties which could have led to a nasty accident. I have just heard from Simon at Meteor who is repairing the car for me that the other side was also cracked, so a potential double failure.

if you own a CSR I would recommend an immediate check of these mounts, it's only by luck that I didn't have what could have been a serious accident.

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Gareth - I am glad to hear of your lucky escape.  

It was after my chat with @SamC that I checked my USA-based 2010 CSR this year.  One side, a cast metal (looks like iron) part was cracked.  The other side, in aluminium, was not cracked and was in good condition.  The cracked part had evidence of corrosion being the cause.  Both have were replaced this month with the steel replacement from Team Leos.  Given my CSR is almost exclusively a track car these days, the consequences of a failure on track are frightening. 

Why I had two different metal parts - one on each side led me to do some investigation.  Its fuzzy but there was a CSR production line changeover point from the cast metal part to an aluminium part around 2010-2013.  All CSRs after 2015 in the USA (that I am aware of - about 6) consistently have the aluminium part.  My 2019 CSR build has the aluminium parts.  Since my experience, a USA Caterham dealer has since detected two cracked rear damper mounts in a 2006 CSR.  

The failure point on the older cars seems to be only happening on the older style cast metal part - but I would assume all are potentially suspect given we don't really know.  

I echo Gareth - check your CSR rear suspension mounts as a matter of urgency.  

 

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Ben, it's got approx 8k miles on it, these are the photos Simon sent me, I haven't seen the failed parts, (I'm off at the Laon Historique this weekend, should have been in the CSR! Going by the size of my wife's suitcase I think she's glad we're in the Cayenne :))

C4718DF9-9BAE-41F3-BB1D-1AD551C5D2C8.jpeg.77a7e7b69e8ed8be582be3ceca5c60ac.jpeg B4E6B22E-6EC2-4342-8327-365844C2681B.jpeg.07b5c831e8326f98aae49112b474fe99.jpeg D1D138BC-9B8B-49AD-9A31-DE2060CBF52A.jpeg.b6e3feb058f320fb827eb4899349036d.jpeg

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Both of these mounts were cast aluminium.

we have since cleaned the "still intact" side up and both holes are cracked right through. interestingly it would seem that this was not down to corrosion between different metals.  Both the Stella collets were free to be phished out with fingers.

 

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  • Leadership Team

I think Sam Coates can provide the correct technical explanation of what is the root cause here.  From memory, his conclusion is that it is not related to usage (excessive hoop stress caused by the tightened tapered fixing in a corrosive environment?) but mainly time based.  So, as I recall, a potential issue for all CSRs, given time.

I'm sure Sam can elaborate.

James

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Interesting feedback.  Thanks for the info Simon.

I'll catch up with SamC tomorrow about this.

I wonder if as a matter of course, all CSR owners should be changing their mounts for the Team Leos ones.  I have been checking mine this weekend as was blatting around Wales, so far nothing suspicious.  Difficult to see the forward part of the clevis, but from the rear:

image_2023-05-29_215838921.thumb.png.cffe5241f214ffd40884814507a494ec.png  

Not sure what spec this is, it's on a 2005 CSR200 but looks in reasonable condition.  Would be interesting to compare to other CSRs out there, if people are taking photos...

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Hi all, when I discovered mine failed I brought it to the materials lab at work and got it analysed.  It failed from stress corrosion cracking as a result of the preload hoop stress generated by the tapered spacer as James says.

The alu they have used is very brittle so they evidently didn't want to clamp across the lugs, and instead used this rather crude expanding collet solution.  To be honest, it is just a horrible design…!

SCC causes tiny pits on the surface of the component where sustained stress is experienced (effect is vastly increased where permanent strain is induced - i.e. material is taken beyond yield – in this case if someone has done it up without a torque wrench because ‘they’ve been tightening bolts since you were in nappies’ and therefore know better!).  This isn’t necessarily the same as the kind of corrosion that you’d imagine on steel etc, it can be barely visible to the naked eye and just cause miniscule surface pitting.  Not saying the two aren’t linked, but they aren’t necessarily the same hence I agree with Simon, I don’t think it is necessarily the steel corroding that has caused the bracket to fail, I think the bracket has done that on its own.

That being the case, it appears that time under load is more important in this case than the actual load seen by the bracket, that just polished off the job, and of 90% of the tails I’ve heard, the force required to finally ping it was small (I broke one of mine open with a screwdriver…).  That would also correlate well with the fact that we are now seeing a raft of these failures (I’m now aware of double figures – I think someone was trying to keep a log somewhere, but can’t remember where).

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Yes, it is truly a horrible and unnecessarily over-engineered design with that collet arrangement, Sam.

Assuming a standard spherical bearing in the bottom of the damper, the typical tolerance on the ball width in the bearing is 0.00 to -0.05mm, so machining the clevis width to within 0.00 to +0.05mm tolerance and using a couple of stainless steel spacer washers either side (to spread the small surface area of the ball near the hole) that should be within +/-0.01mm tolerance for stock shim material, the cumulative max tolerance of 0.00 to -0.12mm shouldn't apply too much strain to the clevis when the clevis bolt is tightened without any need for the complex collet arrangement.

I would estimate from the design that the clevis lugs would have to bend less than 1% at the root if the max 0.12mm gap is closed, well within the elastic strain limit.

The hoop wall will also be thicker within the same component external dimensions (due to the hole only being the bolt diameter), removing the main stress point in the design.

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It looks to me like they defined the kin point of the lower damper mount relative to the rear top wishbone mount and boxed themselves in from a packaging perspective with the driveshaft and wheel bearing bolt bores.

I suspect the people who did the kinematics (Multimatic) and the people that did the design (Titan?) didn't find the right balance of compromise!!

A tightly tolerances clamped joint would have indeed been a better design as you say James, and very achievable with top hats to give rotational clearance etc. 

I plan to continue with my Team Leos brackets and check them periodically. They will probably benefit being replaced in 10yrs time to belt and brace it, but that's a decision for another day!!

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Arh just found this

https://www.caterhamlotus7.club/forum/techtalk/broken-csr-rear-upright-any-experiences?page=8

 

The photo in #11 in this thread made it look different,

...in the linky above the shoulder on the cap head bolt look too short to be fully supported on both sides too, maybe look at getting a longer version and trimming the threaded portion down to suit the overal length.

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The incidence of this problem is worrying, my CSR is one of the last ones to be built 2015.  It is not exactly easy to inspect the bracket in question so I may leave it until the service and meantime source a couple of new brackets.  It is a pity there isn't a close up of the failed bracket but looking at the original thread, I assume this is the culprit which I have circled in red, I also show a graphic of the suspension.

David

Suspension01large2.thumb.jpg.3e6afc2e7694972897463a98869b530d.jpg Suspension02.thumb.jpg.bc98be82e80cc859e3c695075c4da46e.jpg Suspension07.jpg.8a75ae5f1744dc68c5b0eb126c3d1ffd.jpg

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7 Wonders, the Team Leos bracket is identical but made of HE30 which is a pretty reasonable ally without any nasty low elongations etc. it also comes with decent quality stainless bushes and collars.

Doing an effective job of redesigning it will need upright mods or a slight move of the OB damper mount bolt axis.

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David, if you look at my photo in post 11 - this was taken by getting on the floor and looking up at the bracket from behind the car.  Pretty easy to see the condition at least of the rearward part of the clevis.

I've bought the Team Leos brackets and will fit them in the near future.

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Ben, yes I have saved that photo to my dossier on the subject, your bracket looks in good condition and clean so I assume a faulty bracket would show a crack in that mounting.  Maybe a mirror would be required to see the other side of the bracket, I will take a look tomorrow if I get time.  Meantime I have ordered two from Team Leos.

David

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  • 1 month later...

I didn't see this until I did a blatchat search while I was waiting for a recovery truck on the M11 on my way home from Italy. 2,500 miles of touring Europe and then I break down 40 miles from home. That said, I don't think it would have made any difference as I don't think mine were cracked - the problem was I hit a badly repaired pothole on the inside lane which had sunk into the hole, creating a ski jump. Hitting it at 70mph resulted in a massive bang after which the car did not feel right. Seeing blue smoke behind the car meant that I pulled over as soon as I could, which meant continuing until I could safely cross the entry slip road and pull on to the hard shoulder - about 800m or so.

The damper broke free at the bottom and from what I can see so far it is a clean break - I'll know more when I get it cleaned up as the cover on the driveshaft UJ is mangled and there is grease everywhere. The tyre ended up resting on the side skin and lifted up a bit of the skin, cutting a groove in the sidewall. It would have been nasty if the sidewall had gone too!

I am now waiting to hear from the insurers to get it all fixed. That makes 2 claims in one trip (after 20 years with no claims) as someone kindly broke my fog light and dented the rear skin whilst I was parked at the top of Stelvio Pass...

nobody was hurt but it could have been a lot worse. The problem was already flagged to the Highways Agency (2 days prior) and they called me to say it would be repaired overnight  Looking at the comments, (J11, M11j it seems that the holes were huge enough to rock HGVs and cracked a windscreen on a 4x4. I might get some compensation, but it will take a long time and I am not holding my breath.

Steve

I don't know why the 1st two pictures are coming out upside down from my phone...

 

IMG_9263.thumb.jpeg.b538ed952889fc96cf3c3745c1753c72.jpeg IMG_9270.thumb.jpeg.3a40d91ffd4ac56fca9f7954e98c351d.jpeg IMG_9272.thumb.jpeg.cfc70405da8a8e87dd9d2c0e1eb9f012.jpeg IMG_9278.thumb.jpeg.2ed7653acfb72256f9c36d2d99341703.jpeg

IMG_9284.thumb.jpeg.b354276b533ead98ecb367800caa5177.jpeg

 

 

 

 

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