Copper-nickel brake lines on unsprung suspension components?

[IndyIan]

Any worry about copper-nickel brake lines on unsprung suspension components? On my Focus, I replaced a hard line to one of the rear wheel cylinders. The Focus has a trailing arm rear suspension so they use a flex line to the front of the trailing arm and then a 13" steel hard line down the arm to the wheel cylinder. The hard line has some bends but is only supported at each end by the fittings. Its a 3/16 line so it's not that heavy but its going to get a lot of vibration pounding down the road on the unsprung part of the suspension.
Copper-nickel line sure was nice to work with but that softness has me thinking about how much it might flex and its fatigue life.

 

[WyrTwister]

I have done very few brake hard lines ( years ago ) . A few brake flex lines . No copper - nickel hard lines .

If I were you , and I was concerned , I would create some more attachment / supports for the copper - nickel line . Even if they were like theese , attxched with twk self drilling screws ;

https://www.google.com/search?client=firefox-b-1-d&q=wire+ties+sith+hole

Hopefully some one , that knows a lot more than I do , will chime in .

Best of luck to you ,

 

[Dave9]

If you legitimately feel that extra flex will decrease lifespan, put more slack in the line and secure it so it doesn't bump against any (harder metal) surface.

However I doubt it will be a problem. While the copper makes it softer and more flexible, it can flex much more before the fatigue you'd see with standard steel alloy lines.

What was the failure mode of the line it replaced? Rust? If so I wouldn't worry about it, as the CuNi line should resist this earlier failure mode for longer than steel line would.

If you're just not going to be at ease until you have steel line there instead, do that and get it over with - it's not worth losing sleep over.

 

[slacktide_bitog]

You should be more concerned about the wiring in the tailgate

 

[Trav]

No problem whatsoever.

 

[IndyIan]

Originally Posted by Dave9
If you legitimately feel that extra flex will decrease lifespan, put more slack in the line and secure it so it doesn't bump against any (harder metal) surface.

However I doubt it will be a problem. While the copper makes it softer and more flexible, it can flex much more before the fatigue you'd see with standard steel alloy lines.

What was the failure mode of the line it replaced? Rust? If so I wouldn't worry about it, as the CuNi line should resist this earlier failure mode for longer than steel line would.

If you're just not going to be at ease until you have steel line there instead, do that and get it over with - it's not worth losing sleep over.

The line was replaced when I replaced the leaking brake cylinder and the fitting was siezed to the steel line and the line twisted off as the fitting was undone. It was also starting to rust.
I'm not super worried about it, but I believe pure copper lines aren't used for brakes anymore as copper work hardens more than causing them to fail. This line isn't touching anything and should never flex but will be vibrating with road impacts.
https://www.copper.org/applications/automotive/brake-tube/brake.html In table 1. in this link that I think shows that Cu-Ni line starts out about the same strength as steel but reduces to half the strength as steel line after a fatigue cycle test, but I guess its still good enough? A quick search on a Focus forum seems to show lots of people have used copper for this and no one has reported a failure, so I'm probably good!

 

[IndyIan]

Originally Posted by slacktide_bitog
You should be more concerned about the wiring in the tailgate

Yes, I have dealt with that a couple years ago... It seems my splices are holding up so far...

 

[IndyIan]

Originally Posted by Trav
No problem whatsoever.

Excellent! I was hoping to hear from you. I read lots of european cars have used cu-ni lines for a long time, so the "kinks" must be worked out by now.

 

[Trav]

Some of the best car in the world use it, it is really the best unless you off road, in that case stainless is a better option. From the article.

Quote
Users of copper-nickel brake tubing in addition to Volvo include world-class vehicle manufacturers like Rolls Royce, Lotus, Aston Martin, Porsche and, most recently, Audi. Copper-nickel is also used in military, fire fighting and other heavy vehicles