[V6-12v] Re: Stainless brake lines - what's the deal?

The CyberPoet 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 
the lines.

=-= Marc Glasgow

Generally, ask a motorcyclist...
--------REQUOTED -------
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.
> W.Bell
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