[V6-12v] Re: Stainless brake lines - what's the deal?
thecyberpoet at cyberpoet.net
Mon May 17 13:15:53 EDT 2004
Actually, teflon is used because it is less porous than traditional
rubber lines, thus permits less humidity penetration. This is a
separate technology from the steel reinforcement for the exterior of
=-= Marc Glasgow
Generally, ask a motorcyclist...
Some other things for the newbies (the rest of you probably know this
Brake line hoses are made of rubber or synthetic rubber, usually with a
woven nylon integrated into the rubber for strength. Each time you hit
the brakes, the hoses expand a little bit under the pressure, kind of
like a balloon being inflated (only at a reduced rate because they are
thick, and because the nylon helps hold it in shape). Over time, this
inflation-deflation cycle causes the nylon to get stretched and the
rubber to weaken, and the hoses inflate even more. The degree of
inflation under pressure is the amount of power you are producing that
isn't acting directly on the pads, and that translates into the amount
of power that isn't giving you good feedback of what's actually
happening at the pad/rotor interface down at the wheel.
Suzuki, in all it's wisdom, has decided that after four years of
typical use, the brake lines need to be replaced, because they will
have gotten inflated and deflated often enough to both put you
seriously out of touch with the reality of what's happening at the
pad/rotor interface and because they could fail (imagine the balloon
finally popping). If you are harsh on your brakes (city riding, track
riding, putting lots of pressure on the brakes at every red light), you
need to change your brake hoses more often than the standard four year
In an ideal world, you'd be able to use actual formed metal tubing for
your brake lines, but the reality is that your brake lines have to flex
with both the up and down movement of the wheels (both front and back)
and the turning of the front wheel, so only a flexible tube will do,
one which can flex literally hundreds of thousands of times without
failure. Enter metal-shealthed or metal-shealth-integrated brake lines.
These lines are still made of rubber (natural or synthetic compounds),
but a woven/braided metal cover either runs across the outside of the
line, or is within the rubber material itself (often in addition to the
nylon weave). The metal acts as a stronger straight-jacket than the
nylon alone can, preventing the rubber from expanding as much under
inflation, and thus provides significantly better transmission of
what's happening at the pad/rotor interface than regular rubber lines
can. Note that the metal doesn't actually hold the liquid -- it just
restrains the rubber lines. Since the lines still flex lengthwise for
up and down movements of the wheels and turning of the front wheel,
even these lines need to be replaced every four years or so (but they
age more gracefully in terms of performance than stock rubber lines).
Both kinds of lines (rubber and metal sheathed) still permit some water
vapor intrusion into the brake fluid (ambient humidity, as well as
water that splashes on them and water from washing the bike). It is a
slow process, but sooner or later, some water vapor always gets
through. DOT 3 and DOT 4 brake fluids are formulated to be able to
absorb some degree of water into the fluid without permitting it to
separate into a liquid at the bottom of the system (water being heavier
than brake fluid, if it separates, it falls to the low point of the
system). Once this absorbing capability is surpassed, water separates
out within the system. The problems with this are that (a) it rusts in
the inside of your brake calipers, possibly freezing the motion, and
(b) if heated by brake friction, forms steam which becomes air bubbles
(both increasing the pressure on the hoses initially, and being a
compressible gas, removing the ability for you to put significant
pressure on the pads by squeezing the lever).
Most brake fluids change color to a progressively darker color as more
water is retained in the fluid (the primary reason that your brake
reservior has a round window instead of just a line to see the height
is so you can see the brake fluid color). Suzuki's guidelines are to
replace the brake fluid every other year. If you live in a
high-humidity environment, replace the fluid every year. If you brake
fluid is dark brown, cloudy or dirty looking, replace the fluid
immediately. Personally, I recommend replacing the fluid as soon as you
purchase any used bike as well.
=-= The CyberPoet
=-= Marc Glasgow
On Monday, May 17, 2004, at 10:07 AM, Warren Bell wrote:
> I thought the deal with SS brake lines was that the inner hose was
> teflon and the teflon hose had
> much less give when put under pressure. But since teflon is so much
> more "delicate" than the rubber
> hoses it had to be covered with something to protect it, hence the SS
> braid. Furthermore one of the
> problems with the braid is that dirt and grit can get inside of it and
> over time abrade the teflon hose
> causing it to fail. This I thought was the reason some hose
> manufacturers cover the braid in 'rubber'
> to further protect it.
> But this is just my understanding and in no way can I really back any
> of this up with quotes or facts.
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