Stopped at local auto parts store & bought Valvoline synthetic DOT 4 brake fluid. Any harm in adding this to bike which now has Harley DOT 4 ? I'm installing new pads, it's to top off master cylinders.

 

dot 4 is dot 4- do not mix various ratings ( dot 3, dot 5).

while you are at it:

when you push the pistons in to replace the pads, old dirty fluid is pushed up the lines.

crack the bleeder and push the pistons in- that will expel the dirtiest fluid.

than close the bleeder.


and later add clean fluid to the reservoirs

Mike

 

There was a very good article in American Iron magazine +/- 2 months ago on using dino vs. synthetic brake fluid. You should find the article and read it.
The short answer is NO. Do not mix.
The longer answer is that std brake fluid absorbs moisture that naturally occurs in the brake system and that by doing so, does not allow moisture to corrode those metal parts.
Synthetic does not absorb moisture and accordingly, present a whole different set of maintenance issues. Not that it is bad, but different.

 

Thanx to both, think I'll return this & get dino-DOT 4.

 

hmmm the HD dot 4 - I do not know if I would call that "dino".

a fluid which absorbs water is hygroscopic. this fluid can then freeze and the expanding ice can blow out seals in pistons and master cylinders.

all I know is dot 4 is dot 4


Mike

 

Dino meaning produced (refined) from naturally occuring crude oil. And Mike is correct about the definition of a hygroscopic fluid.
We are talking about a sealed system that is affected by condensation within the lines, reservoir, ect. That is very, very small trace amounts of moisture; certainly not enough to freeze and rupture your brake system, but enough to cause oxidation within the system.
Well, at least not cold enough in my part of Tennessee to rupture a brake system.
The point being that it is an very informative article and would encourage anyone to read it.

 

good info. I wouldn't mix. could be bad...also have heard tale of people mixing and having issues in hot weather with breaks locking up that "might" have been because of mixing fluids. Don't think it was ever proven, but still wouldn't take a chance!

 

You can use the fluid you have , and if you are scared vac all of the old fluid out , to be sure.

 

Agree with mkguitar. DOT 4 is DOT 4 and brand does not matter. Do not mix differnet DOT ratings, especially DOT 5 which is silicon based.

 

The US allows oil manufacturers to sell motor oil labeled Synthetic and it in fact is not. Why would brake fluid be under a different set of rules. Who the hell can tell what you are really getting in the US. I put the Valvoline syn in a few months ago with no issues in 2 or 3 thousand miles and don't expect any. I did do a 100% change and will do it every 5000 miles as my $19 Harbor Freight vacuum bleeder does it in 10 minutes. If you see all the crap in your reservoir and calipers you may want to change all of it. Especially in an 05.