BRAKE FLUID, DOT 4 – DOT 5
WHAT’S THE BIG DEAL
April 13, 2006

If you have looked at your brake master cylinder cover lately, you will notice it has changed if you have one of the new Harley-Davidson® models. If you have a 2006, it indicates DOT 4, while your 2003 indicates DOT 5. What is the difference? Simply put DOT 5, is silicone based and does not absorb moisture and does not damage paint. DOT 5 should not be used in any vehicle with anti-lock brakes. The silicone based fluids tend to froth and cause tiny air bubbles when pumped excessively, thus the non use in anti-lock brakes. DOT 3& 4 are hydroscopic meaning they absorb moisture over a period of time. Moisture will cause corrosion in the master and slave cylinders in time if not flushed and replaced at proper recommended times or mileages. DOT 3 & 4 will eat your paint very quickly if left in contact with a painted surface. An open can of DOT 3 or will absorb moisture out of the air very rapidly. DOT 3 or 4 WILL NOT MIX WITH DOT 5.

Can you switch from one to the other? Yes, as long as you change the seals in all cylinders and clean the system really good. I really don’t see the point to switching but others may. If your bike is under factory warranty or you have a extended service contract, you would not want to switch. If you do switch you MUST change the covers of the master cylinders to indicate which type you have or the possibility of mixing the types is greatly increased. Mixing types can have very dangerous consequences.

If you have any questions concerning the use of the different types of brake fluid or the change intervals, please don’t hesitate to contact the service department here at the House of Harley-Davidson & Buell. Again DOT 3 or 4 WILL NOT MIX WITH DOT 5.

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