Here is something I stumbled across and saved.Had it for a while and not sure of the author.
Beginning in 1976, Harley-Davidson used DOT 5 in all its brake systems.
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.
For model year 2005, the FL platform changed to DOT 4.
For 2006, all models except XL went to DOT 4.
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.
Click here to enlarge
For 2007, All models use DOT4.
When working with Any Brake Fluid follow these very important steps;
1. Cover the tank and fenders as an added measure to prevent any spilled brake fluid from coming in contact with paint. Beware of any fluid dripping down the frame tubes.
2. Level the master cylinder BEFORE loosening the cover to prevent spills onto painted surfaces (glycol-based fluids damage paint).
3. Determine what type of fluid is currently in the system, it may have been changed from the factory specification.
4. If glycol-based brake fluid is spilled on paint, do not use a pressure hose to spray it off, as the paint will have softened. Use soapy water, rinse thoroughly and let it air dry.
5. If you suspect that different types of brake fluids were mixed together in the system...you should completely rebuild it, using all new rubber parts, as contamination goes deep into the old parts.
These are just a few precautions you should take when working with brake fluids. If you should have any other questions...Stop by the shop and we'll be happy to answer them for you.
DOT 5.1 ...LIKE TO SHOOT THE DUMBASS THAT CAME UP WITH 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.