DANGEROUS brake pipes

[stevep]

This a heads up to all special owners
The pictures below show the brake pipe that broke on the way back from the Cotswolds a week ago.it went with no warning at all .
It was very scary luckily we managed to stop on a grass verge with no injures or damage to the car or us just very shaken up.

This is a copra nickle pipe fitted new 4/5 years ago when I rebuilt the Lomax with the Guzzi engine.
This is the one from the master cylinder to drivers side disc and broke at the master cylinder fitting end.
I believe this failure was caused by the vibration and constant small movement of the engine in relation to the master cylinder which is obviously fixed to the bulk head although this pipe did have loop in it to try and mitigate any fatigue it did not work for the long term .talking to 2cv owners the problem may have been caused by not having the pipe clamped between the cylinder and brake
Which is the case on the standard 2cvs This could be a reason for the failure .
Moral of the story check the brake fittings and pipes regularly
I am now looking into fitting flexible brake pipes in that area.
Stay safe
Steve

IMG_6Sep2021at165511.jpg (450.95 KiB) Viewed 17360 times

IMG_6Sep2021at165652.jpg (5.23 KiB) Viewed 17360 times

and keep on revving

[2cvman]

Perhaps it should be like this.

3104D8D3-9563-455D-9851-811B5DCBD86B.jpeg (15.05 KiB) Viewed 17356 times

If system is LHM ensure the correct LHM flexible hose is used see Burton or Fransoze.

[AlanM]

I’m converting Mungo to a tandem master cylinder and LHM brakes.

Alan

[Ken Hanna]

stevep,
I'd doubt that it's the pipe which is 'dangerous', much more likely to be incorrect fitting that's the culprit.
Fwiw, I've seen more than a few Specials where this detail has been ignored...

https://flic.kr/p/2mn22sE
Ken

[AlanM]

Thanks for that Ken, all useful information for when I come to fit my brake pipes.

Alan

[cmwbob]

AS with most things like swords, knives etc they only become dangerous once a human gets involved.

[Davidm]

stevep,
I'd doubt that it's the pipe which is 'dangerous', much more likely to be incorrect fitting that's the culprit.
Fwiw, I've seen more than a few Specials where this detail has been ignored...

https://flic.kr/p/2mn22sE
Ken

I 'm sure you are correct, Ken. But - - -
I believe the standard 2cv brake pipe is steel which has a well defined fatigue limit and steel components can be designed to have an infinite life if subjected to repeated cycles below that fatigue limit.
Copper alloys will not have this property so special care should be taken when fitting such piping subject to any repeated movement.
Is there substantial experience with 2cv's where cunifer has replaced steel brake pipes using the same fixing method I wonder ?
Davidm

[Ken Hanna]

David,
if you're asking whether I've ever witnessed fatigue failure of a cupro-nickel brake pipe, the answer would be 'no'...
.
Found this document online, which seems to suggest that copper and its alloys are resistant to fatigue.
Fatigue Data Compilation and - Evaluation of Fatigue on Design
https://publikationen.bibliothek.kit.edu › ...
PDF
3.3.3 Copper and copper alloys ... in general no threat to life or other severe conditions.

.
https://flic.kr/p/2mnCXtb

Ken

stevep,
I'd doubt that it's the pipe which is 'dangerous', much more likely to be incorrect fitting that's the culprit.
Fwiw, I've seen more than a few Specials where this detail has been ignored...

https://flic.kr/p/2mn22sE
Ken

I 'm sure you are correct, Ken. But - - -
I believe the standard 2cv brake pipe is steel which has a well defined fatigue limit and steel components can be designed to have an infinite life if subjected to repeated cycles below that fatigue limit.
Copper alloys will not have this property so special care should be taken when fitting such piping subject to any repeated movement.
Is there substantial experience with 2cv's where cunifer has replaced steel brake pipes using the same fixing method I wonder ?
Davidm

[Davidm]

Ken
I could not find the 3.3.3 ref but the chart of typical endurance limit/uts ratios for different materials is very useful and in line with what I expect -
For carbon steels expect approx. endurance limit of .5 x UTS for 10^6 cycles and beyond for infinite life.
For copper and its alloys the endurance limit is shown as min. .25 x UTS and - the UTS for copper alloys is less than for steel.
As copper and its alloys do not have a well defined fatigue limit I note that a fatigue life of 10^8 cycles is chosen.

I just wanted to note that using cupro- nickel piping as a replacement for steel would require at least as much care in how it is mounted if subject to cyclic movement or stress.

I fitted cupronickel brake pipes from Bonaparte to my Pembleton and I did wonder about the fatigue life of the rear brake spiral and the pipe between master cylinder and caliper. I convinced myself that movement of the rear suspension arm and internal spiral is small compared to 2cv and a failure of the rear brake should not be too catastrophic . But I still have a nagging doubt about the master cylinder to caliper pipe.
When i looked on the Franzose site I found cupronickel piping for fixed locations but "high quality steel" for the curly pipe and master cyl./caliper pipe so I wondered if this was because of caution prompted by fatigue considerations ?
I see Burton offer stainless steel brake piping throughout.
David

[notsmartcar]

When I bought pipes from Bonapart when it was still in the uk before being sold he told me for insurance purposes he had to make a jig to subject his rear pipes to movement and ran it for months to prove their ability to not fatigue