> It was my opinion that copper should not ever be used as brake lines and was
> in fact DOT illegal.
Common copper tubing, like those used for water or refrigeration lines, is
definitely not suitable for brake lines.
However, there is a special copper/nickel/iron alloy that has been specifically
developed for brake lines, that seems to be OK. Sometimes known as Cunifer
(since Cu, Ni and Fe are the symbols for the main alloy elements). It's been
used in other countries for some time now, and seems to work quite well,
particularly in areas where salt, moisture and sand are found. (The tin-plated
steel we use in the US may rust through if the tin coating is abraded away by,
for example, gravel thrown from a gravel road.) Although Cunifer does have some
"copper" color to it, the color is noticeably lighter than that of pure copper;
more like the color of a new US penny.
But you are quite correct, even Cunifer is not approved by the DOT. I expect
that will change in coming years, but AFAIK it hasn't changed yet.
> Something about the high hydraulic pressure and the copper be easy to be
> mechanically damaged and cause failures.
I believe the main issue (assuming you use tubing rated for the pressures
involved), is that copper can work-harden if it is repeatedly flexed, as might
happen from vibration in a car environment. The work-hardening weakens the
tubing, and of course any weakening would be discovered at the worst possible
moment, during a panic stop. The Cunifer alloy reportedly does not suffer from
this problem ... but good design dictates that all brake lines should be
adequately secured to ensure they don't flex due to vibration.
Another advantage of Cunifer is that it's somewhat softer and easier to bend
into shape without crimping. Probably also easier to form the proper flares
(offering a higher chance of success at making a good one), but I haven't tried
that myself (yet). In retrospect, I wish I had used it the last time I had to
fabricate a brake line.
Randall
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