I recently purchased a 2005 Road King. The Service manual calls for DOT 4 brake fluid but when I look at the 2 master cylinders, the rear master cylinder cover is stamped DOT 4 and the front master cylinder cover states to use only DOT 5. Is it possible that I have 2 different fluids in the 2 systems? Has anyone else seen this?

 

It is possible someone changed the cover. Go with the manual and use the same for both. Also I believe dot 4 and dot 5 are both synthetic.

 

Dot 5 is silicone based. Dot 3,4,and 5.1 are compatible. The number is how much heat they can handle. 05's came with Dot 4. If some one changed the front to Dot 5, I would change back to Dot 4....

Trucky911

 

Do not use the wrong fluid. Go with what the manual specifies. Someone must have changed the cap on one of them. DOT 4 and 5 are different and should not be interchanged.

 

HD used DOT3/4 for years up until 1976, then switched to DOT 5. Then in mid-2000's on SOME bikes went back to DOT 4 and left others at DOT 5...Now all HD's are back to DOT4.

DOT 5 has a higher boiling point but is a different type of fluid and does not disperse water like DOT 4.
DOT 5 must be bleed often and flushed if system disturbed to maintain top performance.
DOT5 is basically a racing application, for full size cars, Non-ABS, or some race bikes.

I would stick with DOT4.

 

DOT 5 is purpleish and DOT 4 is yellowish

 

DOT 5 doesn't attract any water, it is silicone. 3 and 4 are mineral oil based.also, 3,4 will strip paint,5 is paint safe..if you don't know what is in there, it is best to flush the system and put in fresh.after flushing with brake cleaner(you have to take everything apart)you can use any fluid you want, but it is less complicated to just use what the bike calls for. if you mix mineral oil and synthetic, it will turn to jello and plug everything up

 

if you mix mineral oil and synthetic, it will turn to jello and plug everything up

I'll second that...

 

Thanks guys. I've come to the conclusion that the previous owner changed the front master cylinder cover at some point and put a DOT 5 cover on. I am flushing both the front and rear systems and putting in DOT 4 per the manual. I've also ordered a chrome cover with the DOT 4 warning label for the front.

 

04 FSM says DOT 5, my covers say dot 5, my fluid is yellow......