There are three reasons to install stainless-steel brake lines:

They look racy.
They don't swell like rubber lines, so they can potentially firm up your brake pedal.
If you're doing a lot of off-road driving, the stainless-steel braid may protect your lines from being punctured by rocks or whatever.
Here's the thing, though: Since stainless-steel lines don't bulge as they age, and since the inner Teflon lining is hidden behind thebraid, there's no easy way to inspect the lines for warning signs of imminent failure. This is no big deal on a race car, since the lines are (or should be) replaced at least once a season. On a street car, where most people are likely to let YEARS go by without even looking at their lines, it can be an issue.

I define "correct" hose-ends as Earl's Speed-Seal (the new name for Fluor-O-Seal) or Aeroquip Super Gem, and "real" hose as Earl's Speed-Flex (the new name for Fluor-O-Flex) or Aeroquip.

Anyway, Speed-Seal hose-ends work just like Earl's Swivel-Seal ends; the hose-end can swivel after assembly. The nipple/cutter assembly on these ends (and on Aeroquip Super Gem ends) was specifically developed to prevent blowoff of the hose-end..

THIS IS IMPORTANT: The lines that your performance-parts distributor will sell you are made with no-name hose from God-knows-where (probably Taiwan), and the hose-ends are just swaged-on fittings that are an invitation for disaster. I won't run these on my car, and I don't recommend that you run them on yours, either.

There are now "DOT-approved" stainless-steel lines. I have no idea what they are, but I suspect that they STILL use cheap-*** crimped-on hose ends. Until my suspicions are disproven, I won't run THEM on my car either.

New information that I just received: Stainless steel lines have been known to fail when dirt gets between the outer braid and the Teflon lining... As the braid moves back and forth, the dirt abrades the Teflon and can make it rupture. If you look at stainless-steel lines on motorcycles, you'll see that many of them are encased in plastic tubing, apperently in an effort to eliminate this problem. If I don't sell my car before it's time to replace my lines, I'll probably put heat-shrink tubing around the new ones.



Reasons To Avoid SS Braided Lines
[BDV] Well it happened. Someone in a Buick tried to terminate his wife's life and my NSX. I panic braked, downhill, at 35 mph and managed to stop just before my two year old Comptech stainless brake-line ruptured. The pedal went to the floor. The failure was right where the plastic support is near the caliper, which is supposed to stop these kinds of things from happening.

I remember the FAQ discussing this issue, and thinking it would never happen to me. Thank God it wasn't at the end of the back straight at Road Atlanta.

For all you our there with stainless lines. Beware. My braiding actually burst.



[DH] ...it turns out that my aftermarket steel braided line purchased 3 years ago (can't remember the vendor name, I got the lines from Rod Millen Motorsports) separated at the caliper. The line goes into a screw on the caliper which has a hollow fitting for the hose to go over, and apparently I blew it off the fitting.



[FG] [the lines bursting] is the risk that you take with stainless lines. Otherwise, don't you think all manufacturers would have made them standard? Among the BMW and PCA club members I talk to, most shy away from stainless lines unless they are religous about changing the lines every year or two.



[NM] I too thought that stainless steel lines / fittings were the important to high performance braking and was considering it too. After talking to Randy M. at RM Racing I was convinced this was not a good idea for a production car.

Randy told me he does not recommend these NOR does he use them in the RM Racing NSX. The braking and rumored flex are not affected by the plastic brake lines. He said that one person who had them installed had them come apart right after leaving the installer and was in an accident in their NSX. Maybe this is why Ferrari uses the plastic lines in their production cars too. BTW - I can not recall a single member on this list ever experiencing a problem with the plastic lines failing. A few have suspected (right or wrong) that some perceived braking problems were the result of the plastic lines - but that is another story.

I may not have all the details, but I bet if you private Randy you will get the whole scoop.



[HPA] My $.02 again (long winded as usual): SS lines are tough to a point and are a special application product (i.e. for racing and usually replaced between races just as tires are replaced regularly throughout a race). The SS braiding not only protects the "rubber" beneath from outside physical damage but also act as a girdle that lessens brake line flex (swelling).

On older OE lines with a partner applying the brakes I can see the lines flex, tense and swell slightly. The SS braiding lessens the amount of this flex and you notice it as a firmer pedal feel (fluid type contributes to this as well). They look good, last awhile, then once you get it out of your system you usually wind up going back to OE lines, unless track events are your life and you don't mind this short coming.

Remember, this race inspired product was invented to protect brake lines from track debris left by accidents the driver sometime has no choice but to drive through. The firmer pedal and faster piston actuation was a side benefit. The "look" is just that. If you want long lasting (relatively speaking) stick to OEM lines. If you want more protection and performance try synthetic cloth braided lines (if anyone is specifically marketing them for the NSX I don't know; if not, custom made by a fluid fastener maker is an option if you can find someone willing to make them for you). That last comment is an option not a recommendation.

If I wanted more protection I'd just place a plastic braided sleeve over the OE lines during a line change. OE brake lines are really good quality for what I've encountered under Honda's and Acura's thus far. If you drive hard and brake hard just inspect your lines regularly and plan on replacing them about every 2-3 years or whenever the fluid is recommended to be flushed and replaced. Might as well get the Speed Bleeder replacement fittings (www.speedbleeder.com) while you're at it and get some Motul or Lockheed fluid.

Note: Used to be that rubber composition allowed you to guesstimate the wear of various belts and hoses with warning signs such as fraying, cracking, mushiness or brittleness. New rubber composition still looks good past its recommended change interval. You wouldn't take a chance on missing your timing belt change interval and having the valve service
missed either, would you? That's a very expensive chance.

No matter how good (or excellent in Honda's/Acura's case) a product is the manufacturer recommendations are there for a reason. Some stretching of guidelines are forgivable by the car while others are not. Common sense should rule that no matter what go-fast improvements are made stopping should always be more important. With the emphasis there proper preventive maintenance is the key. Forums such as this help to fill the knowledge database when experience is unavailable.



Inspecting SS Brake Lines
[BH - 98/8/24] Assuming they are installed properly with appropriate slack in the lines, all you can do is to inspect them visually, and make sure there are no obvious kinks or damage to the lines. I make sure the fittings on the ends of the lines look securely attached to the lines. The stainless lines commonly fail at the fittings because there is not enough slack in the line to absorb the wheel's full range of motion from steering input or suspension travel. I also make sure there is the normal amount of slack in the lines.



[BSD - 98/8/24] Look for any fluid leaks of course, plus for any frays, or crimps or anything that doesn't look perfect with them.




What Are "DOT-approved" SS Lines?
[AWN] A few people have asked me to explain the difference between "DOT-approved" and non-approved stainless-steel brake lines. This explanation is pretty long, but I think it'll explain everything so I won't ever have to post another message on the subject... I'll just refer anyone who asks to the Porschelist searchable archives.

First, a quick explanation of what stainless-steel brake lines ARE:

The brake lines we're talking about are the flexible ones that connect between the hard lines (i.e., the inflexible tubing) in the car and the brake calipers on the wheels.

They've traditionally been made from rubber tubing, with steel or aluminum connectors crimped onto their ends. Nearly all passenger cars are shipped with rubber brake lines, and they hardly ever fail.

"Stainless-steel" lines are made of Teflon tubing, not rubber. Teflon has a number of advantages over rubber; the chief ones are that it doesn't expand under pressure and it doesn't deteriorate with age. It also resists high temperatures and is chemically inert, so it's compatible with all brake fluids.

However, Teflon is pretty fragile, so it has to be protected from physical damage (chafing, flying rocks, etc.). Although some manufacturers armor their Teflon hoses with Kevlar, most protect the Teflon with an external sheath of braided stainless-steel wire... So that's why armored Teflon hose is usually called "stainless-steel hose". There's no such thing as a stainless-steel brake line that's "not lined with any material"; ALL stainless-steel brake lines are really Teflon lines with a protective stainless-steel-braid cover.

The ends of the hoses have to be securely attached to the brake calipers and the hard lines, so each hose is terminated by threaded hose-ends.

Those hose-end fittings can be attached to the hoses a couple of ways.

The cheap way is to crimp or swage them onto the hoses, like the fittings on rubber hoses. The more-expensive way is to use a two-piece replaceable hose end that captures a portion of the hose between an inner nipple and a concentric outer socket. These hose-ends (often referred to generically as "Aeroquip fittings" because they were invented by the Aeroquip Corporation) are used EVERYWHERE on aircraft and race cars.

Ok... So what's required for a stainless-steel brake line to be DOT-approved?

First, I should point out that there may be lines available that meet all the DOT specs, but are non-approved only because they haven't been submitted to the DOT for approval.

Manufacturers can't legally say that their lines are approved -- even if they KNOW that the lines meet all the DOT specifications -- without actually submittimg them to the DOT.

For that reason, stainless-steel brake lines can fall into three categories:

"DOT approved" - These lines have been submitted to and approved by the US Department of Transportation.

"non-approved" - These lines don't have a DOT approval, either because they don't meet the specs or simply because they haven't been submitted for testing.

"non-conforming" - These lines are non-approved (and non-approvable) because they fail to meet the DOT specs.

Ok...

The safety standard that brake hoses must meet is called Federal Motor Vehicle Safety Standard 106; if you have a copy of the Code of Federal Regulations handy, it's in Title 49, Volume 5, Subpart B, Section 571.106.

The section that applies to hydraulic hoses is about six pages long, and it covers everything from labeling requirements to pressure and temperature testing.

One important thing to note -- this'll come up later when I explain why the "best" hose assemblies can't be DOT approved -- is that each of the requirements in the Standard carries the same weight; if a hose fails to meet ANY requirement, it won't be approved.

Hypothetically, therefore, a hose which met all the performance specs but was labeled in lowercase letters (the Standard requires block capitals) would fail to be approved.

Also, some of the features required by the Standard provide a certain amount of "idiot-proofing", but at the expense of absolute maximum strength or safety... It's the same sort of mandated mediocrity that forced Ferrari to replace the stock 5-point safety harnesses in US-spec F40s with those ridiculous motorized-mouse single shoulder belts.

Anyway...

Most of the "performance" specs in the Standard (i.e., burst strength, compatibility with brake fluids, tensile strength, expansion under pressure, etc.) are easily met by all halfway-decent hydraulic brake hoses, but there are a couple of tests and requirements that are particularly difficult for stainless-steel hoses to meet.

Those requirements are:

1. The manner in which the fittings must be attached to the hose.

FMVSS 106 specifies that "Each hydraulic brake hose assembly shall have PERMANENTLY ATTACHED brake hose end fittings which are attached by deformation of the fitting about the hose BY CRIMPING OR SWAGING." [Emphasis added]

The idea is that, since crimped-on fittings can't be loosened, a stupid end-user won't be able to screw with and weaken them.

This is a good thing from a product-liability point of view, I guess... But it means that any hose assembly which uses the very best fittings available -- like the nipple-and-cutter Aeroquip Super Gem or Earl's Speed Seal -- is non-conforming and CAN'T be DOT-approved.

2. The "whip-resistance" test.

This test involves mounting the hose on a flexing machine, pressurizing it to 235 psi, then running it at 800 RPM for 35 hours.

When steel-armored hoses were run through that test, it was found that the hoses tended to bend right at the junction between the hose and the hose-ends. After a while, the stainless-steel braid would start to tear, and the broken wires would cut into the inner Teflon liner, causing it to fail.

One brake-hose manufacturer fought to modify the whip test, claiming that their stainless-steel hose could easily comply with the test if only a supplemental support were used during testing to move the flexing-point away from the hose-ends.

The NHTSA ruled on the issue in August, 1996, deciding to allow manufacturers to use the supplemental support... But only on the condition that the same support was used when the hoses were installed on a real car.

FMVSS 106 was modified to include the use of the support, and the new rules went into effect in October, 1996.

"DOT-approved" stainless-steel brake hoses went on sale immediately thereafter.

So... Now that you know the whole story, you can make an informed decision as to whether you want to put these things on your street-driven car.

If you decide to install them, you need to be aware of a few things:

When you install them, you must make SURE that they can't kink, twist, or stretch under any combination of wheel droop, bump, or (for the front wheels) steer.

The stainless-steel outer braid will cut through anything against which it rubs, so you have to make sure that the lines don't rub back and forth over anything important.

Stainless steel lines have been known to fail when dirt gets between the outer braid and the Teflon lining... As the braid moves back and forth, the dirt abrades the Teflon and can make it rupture. If you look at stainless-steel lines on motorcycles, you'll see that many of them are encased in plastic tubing, apparently in an effort to eliminate this problem. The tubing also helps considerably with the abrasion issue mentioned above.