Folks,
I replicated this from the Volume 3, Issue 2, 1999 issue of "Battle 2win"
magazine (regarding the '00 model Buells):
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Fluid mechanics-
A further across the board change to the '00 brakes is the switch to DOT 4
brake fluid from DOT 5. According to Buell engineer Doug Manternach, Dot 4
fluid performs better "at the extreme end of braking." This is a technically
interesting change, and is sure to be controversial. In the Winter 1996
issue of Battle 2win, Tech editor Kip Woodring wrote, "...there is
absolutely no good reason not to use DOT 5 brake fluid." And in the context
of street motorcycles, we continue to stand by that assertion. So why DOT 4?
We have to delve a little into the technical side to explain that.
Manternach is, of course, correct. Most, if not all racing vehicles, because
of the braking extremes they employ, use DOT 4 -- or in some cases DOT 3 --
brake fluid. And given Erik Buell's love of racing motorcycles it is
understandable that he would want to go with the best. But, there are
definite drawbacks to using DOT 4 fluid on a street bike.
DOT 4 is an organic combination with a mouthful of names, polyalkylene
glycol ether -- popularly known as "glycol." It has two attributes that make
it a nuisance for street use. First, it is hygroscopic. That is, it absorbs
water; as much as 6 percent, by weight. Given the heating/cooling cycles
that brakes go through, inevitably moisture will be introduced to the
system, corroding the components, and contaminating and impairing the
fluid's effectiveness. Yes, this can take a long period of time, but it will
happen. Secondly, glycol will corrode paint and powder-coat. This becomes an
issue due to its water-attracting properties a reduced service interval is
necessary, therefore increasing the possibility of weepage, spillage and
other opportunities to mess up your paint when the fluid is changed.
Regarding that service interval, Manternach couldn't tell me what it would
be on the '00 models, but agreed that more attention to the condition of the
lines and fluid replacement will be necessary.
DOT 5, on the other hand, is (almost exclusively) a synthetic,
silicone-based fluid. It is not hygroscopic (or very significantly less so),
is friendly to paint, and has longer service interval. Good stuff, uh? Yes,
to a point. A point at which Buell has decided that owners pass enough to
justify the hassles of DOT 4. To explain...
One of the metrics of brake fluid is its boiling point; both "dry" (new
fluid) and "wet" (used fluid). Dry DOT 4 will boil at around 450 degrees
Fahrenheit; DOT 5 can be taken to 500 degrees F, and beyond. The wet temps
average about 120 degrees less, in each case. Higher's better, right? Yes,
but at about 275 degrees some of the additives in silicone-based DOT 5 fluid
begin to "gas off," which introduces air into the system. This, in turn,
gives a soft, spongy feel to the brakes. This is why, at the higher
operating temperatures, DOT 5 brake fluid is considered to be about four
times more compressible than glycol (DOT 4) fluids and, we believe, is the
primary reason Buell has made the switch for 2000.
Don't connect the DOTs-
This change in precious fluid also necessitated the replacement of the rear
brake line; the old one was powder-coated, the new one -- recognized by its
dark green color -- is zinc dichromate plated, precluding the possibility of
corrosive damage to the line. The front line is the same, as it is a
stainless steel wire braid. And by the way, if you're kicking around the
idea of converting your pre-'00 Buell to DOT 4, forget it. DOTs 4 and 5 are
incompatible (organic vs. synthetic) and most experts agree that it is
almost impossible to completely flush a brake system. If you're convinced
that DOT 4 is the way to go you'll have to replace all the brake components
that came in contact with brake fluid. The front master cylinder is also
new. It has an additional plate above the diaphragm (not DOT 4-related) and
a new cap that spells out the fluid to be used...
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I wanted to introduce an 'authority' into this discussion. Not that it's
correct just because it's in print, but I hope it answers some questions.
David Randall
'67 'B-GT
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