One of the things preventing an easy switch is that DOT 3/4 and DOT 5 cause
different rates of swelling in the seals, so a switch in fluid will lead to
an almost immediate failure in sealing of the system. DOT 5 also seams to
be able to find points to leak from that DOT 3/4 will not, but since every
other fluid in MGs leaks I don't consider this a factor.
----- Original Message -----
From: David Randall <firstname.lastname@example.org>
To: james <email@example.com>; <firstname.lastname@example.org>
Sent: 26 March, 2002 11:25 AM
Subject: Hydraulics -- DOT 4 (glycol) vs. DOT 5 (silicone):
> I replicated this from the Volume 3, Issue 2, 1999 issue of "Battle 2win"
> magazine (regarding the '00 model Buells):
> 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
> 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
> of street motorcycles, we continue to stand by that assertion. So why DOT
> We have to delve a little into the technical side to explain that.
> Manternach is, of course, correct. Most, if not all racing vehicles,
> of the braking extremes they employ, use DOT 4 -- or in some cases DOT
> 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
> it a nuisance for street use. First, it is hygroscopic. That is, it
> 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
> happen. Secondly, glycol will corrode paint and powder-coat. This becomes
> 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
> 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
> is friendly to paint, and has longer service interval. Good stuff, uh?
> 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
> 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
> brake line; the old one was powder-coated, the new one -- recognized by
> dark green color -- is zinc dichromate plated, precluding the possibility
> 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
> 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
> 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)
> a new cap that spells out the fluid to be used...
> 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