Ok, 2006 Street Bob. Owner's Manual says DOT4, Service Manual says DOT4, but the sticker on top of the reservoir says DOT5. So anyone know which one it really is? Does it matter? I know you can't mix the two.

 

Does your bike have the original reservoir or has it been replaced?

 

Or reservoir cap. If you've replaced your cap with an aftermarket, it might be that the sticker is wrong.

 

Should be 4. I don't know why your cap would say 5.

 

Get some Dot 4 and Dot 5 and place a bit of each in two paper cups. The take some brake fluid out of your master cylinder reservoir and add a few drops to each cup. Four and Five won't mix and you'll see it straight away. if you want to change grades you can flush the entire brake system out with denatured alcohol and then run either grade you want.

 

Have you checked both reservoir caps? From what I can make out Harley changed over to DOT4 from DOT5 around the model year of your bike. As others have said you may have a replacement cap, with the wrong writing on it. Check the other cap and let us know what you find!

Whatever you do, don't mix DOT4 and DOT5. That is why you need to get to the bottom of this.

 

What color is the fluid? Dot5 starts out purple and turns yellowish, Dot4 doesn't look the same, but the test noted above about mixing is also an easy way.

 

Great advice!! I dont recommend switching. I had some problems last year switching fluids....After a mix up. I flushed everything and ended up replacing everything including the lines in order to get a firm brake.

 

So other than the no mix requirement, is there a functional difference between DOT4 and DOT5 brake fluid?

Sorry if this is just too stupid a question for words.

USMAMule

 

Dot5 is immune to water infiltration for the most part, it also is not harmful to paint. It does tend to suspend air more so than Dot4 which is why it seems to be harder to bleed on a front brake.