I wrote a couple of widely-quoted and -plagiarized posts on the topic 25+ years ago, shortly after DOT-approved braided lines were first made available.
When I wrote them, I believed that the only safe braided lines had to have Aeroquip/Earl's-style swiveling nipple/cutter hose ends (which couldn't be DOT-approved), but that those lines were only appropriate for street cars if you were willing to do frequent inspections/replacements. At that time I was running custom Earl's Speed-Seal/Speed-Flex braided lines on my Porsche (and inspecting them regularly), and OEM rubber lines on my other cars (including the NSX).
Since then, my understanding has evolved, for two reasons:
- I have access to more data, or at least more anecdotes. DOT approval has led to much more usage of braided lines on street cars, and the internet has made it easy to see people's experience with them.
- I think about human error a lot more now. Even though a properly assembled and maintained braided line made with Aeroquip's reusable fittings is "better", an OEM line made with crimped fittings is safer from human error -- e.g., dumb humans can't accidentally loosen the connection between the hose and hose-end.
I now wouldn't use anything but OEM (usually rubber) brake lines on any car that is ever driven on the street. I wrote something elsewhere last year explaining why; here's a copy:
Rubber lines in good condition provide just as firm a brake pedal as SS lines. And rubber brake lines are basically 100% reliable. You should probably change them every 10 years or so, but if you let them go for 20 years they'll almost certainly still be fine. And if they're not, the typical indication of trouble is pretty benign: a pad starts to drag because the rubber hose has swelled enough to restrict fluid from being pulled back away from the caliper, or the pedal gets soft (and flushing the fluid doesn't fix it) because the hose has started to weaken and balloon.
In the USA alone, people drive 3 trillion miles per year with rubber lines. Most drivers have never ever replaced a brake line, and yet you never hear about catastrophic failures due to manufacturing or design defects.
Aftermarket stainless steel lines, on the other hand, are only installed on an infinitesimally small fraction of cars, but if you read any auto forum you'll see that they fail all the goddamn time.
And they fail with no warning, because the Teflon hose inside the steel braid doesn't gradually swell, it just suddenly cracks. Or the crimped-on fitting -- the only type allowed by the US Department of Transportation -- just blows off the end of the hose. Or the hose is the type with an external support to prevent it from flexing right at the fitting, but the support isn't installed correctly so the braid flexes at the fitting and frays, then cuts through the Teflon. Or the hose twists or kinks as the wheel moves, in a way that wouldn't be a problem for rubber hose but which fatigues the SS hose until it fails. Etc.
For a racecar that's never driven on the street, DOT-approved lines aren't necessary, so you can use real aerospace-style SS lines with two-piece Aeroquip-style fittings. And if you inspect them and/or replace them every season, those fancy lines will work fine. But if you drive on the street, it's my opinion that you should use the OEM rubber lines because:
- They almost never fail.
- They usually give plenty of warning if they ever are going to fail.
- They won't disqualify your insurance claim in the very unlikely event that they do fail.
