glider
10-27-2007, 08:19 PM
Some facts about brake fluids.
DOT 5 brake fluid is a silicone-based fluid and is not compatible with DOT 4. It is also less suitable than DOT 4 for ABS systems, because of its higher compressibility.
DOT 5.1 brake fluid is a low-viscosity, high-temperature fluid compatible with DOT 4 and DOT 3. Its low viscosity makes it ideally suited for ABS systems, where it helps the system modulate the braking pressure more easily. Its higher wet and dry boiling points should make it more resistant to brake fade under heavy use. I have had no problems with the braking system since installing this fluid.
DOT 5 and DOT 5.1 are very different standards, confusingly named by the US Department Of Transportation. Of the two, only DOT 5.1 is compatible with DOT 4. Do not use DOT 5 fluid unless you have a good reason and know how to purge the system of all DOT 4 fluid before hand (this usually requires complete dismantling of the braking system and cleaning of the individual components with a suitable solvent). Mixing DOT 5 fluid with any traces of DOT 4 will form precipitants that will clog the braking system.
Harley sells DOT 5 Brake Fluid with the following disclaimer: "Fits all models (except '05-later Touring models, '06-later VRSC™, Dyna®, Softail® and '07 Sportster® models)."
Harley sells DOT 4 with this disclaimer: "Fits '05-later Touring and '06-later VRSC™, Dyna® and Softail® and '07 Sportster® models."
Here's an interesting read on the fluids.
D.O.T. 5 Brake Fluid (http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html)
DOT 4, like DOT 3 and DOT 5.1, is a polyethylene glycol (http://en.wikipedia.org/wiki/Polyethylene_glycol)-based fluid (contrasted with DOT 5 (http://en.wikipedia.org/wiki/DOT_5) which is silicone (http://en.wikipedia.org/wiki/Silicone)-based). Fluids such as DOT 4 are hygroscopic (http://en.wikipedia.org/wiki/Hygroscopic) and will absorb water from the atmosphere. This degrades the fluid's performance by drastically reducing its boiling point. In a passenger car this is not much of an issue, but can be of serious concerns in racecars (http://en.wikipedia.org/wiki/Racecar) or motorcycles (http://en.wikipedia.org/wiki/Motorcycle).
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DOT 5 brake fluid is a silicone-based fluid and is not compatible with DOT 4. It is also less suitable than DOT 4 for ABS systems, because of its higher compressibility.
DOT 5.1 brake fluid is a low-viscosity, high-temperature fluid compatible with DOT 4 and DOT 3. Its low viscosity makes it ideally suited for ABS systems, where it helps the system modulate the braking pressure more easily. Its higher wet and dry boiling points should make it more resistant to brake fade under heavy use. I have had no problems with the braking system since installing this fluid.
DOT 5 and DOT 5.1 are very different standards, confusingly named by the US Department Of Transportation. Of the two, only DOT 5.1 is compatible with DOT 4. Do not use DOT 5 fluid unless you have a good reason and know how to purge the system of all DOT 4 fluid before hand (this usually requires complete dismantling of the braking system and cleaning of the individual components with a suitable solvent). Mixing DOT 5 fluid with any traces of DOT 4 will form precipitants that will clog the braking system.
Harley sells DOT 5 Brake Fluid with the following disclaimer: "Fits all models (except '05-later Touring models, '06-later VRSC™, Dyna®, Softail® and '07 Sportster® models)."
Harley sells DOT 4 with this disclaimer: "Fits '05-later Touring and '06-later VRSC™, Dyna® and Softail® and '07 Sportster® models."
Here's an interesting read on the fluids.
D.O.T. 5 Brake Fluid (http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html)
DOT 4, like DOT 3 and DOT 5.1, is a polyethylene glycol (http://en.wikipedia.org/wiki/Polyethylene_glycol)-based fluid (contrasted with DOT 5 (http://en.wikipedia.org/wiki/DOT_5) which is silicone (http://en.wikipedia.org/wiki/Silicone)-based). Fluids such as DOT 4 are hygroscopic (http://en.wikipedia.org/wiki/Hygroscopic) and will absorb water from the atmosphere. This degrades the fluid's performance by drastically reducing its boiling point. In a passenger car this is not much of an issue, but can be of serious concerns in racecars (http://en.wikipedia.org/wiki/Racecar) or motorcycles (http://en.wikipedia.org/wiki/Motorcycle).
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