silicone

Not all brake fluids are created equal and not all are compatible. There are three grades of brake fluid commonly available: DOT 3, DOT 4 and DOT 5. DOT 3 and 4 are glycol-based fluids and though these 4 fluids are often used in automobiles, you might not want to use them in your motorcycle because they absorb water from the environment and they attack most paints.

DOT 5
DOT 5 fluid, by contrast, is silicone based, meaning a higher boiling point, no tendency to absorb water and no reaction when spilled on a painted surface. It costs more and is reputed to be slightly compressible, though street riders never seem to notice any difference in feel or effect.

New Harley-Davidsons have used silicone-based fluid since the early 1980s and the fluid you will find on the shelf of the dealership or quality aftermarket shop is probably DOT 5.

No matter what you use, remember that the two types are not compatible and should never be mixed. This means you need to use the same fluid used in the donor bike when new – or flush the old fluid out of the donor bike’s components. Given the fact that the donor bike components are used, the flushing is probably a good idea regardless of the original fluid used in that system.Silicone