brake fluid

[racerxnico]

This question isn't really for the 'GS', but the bike parked next to it in my garage.

It is a little project bike that I am turning into a cafe racer. They don't make rearsets for the original bike and I don't think I have the skills to fabricate my own. I do have enough ability to fab up some brackets though, so when some cheap rearsets from a 2005 Kawasaki Ninja 250 turned up on ebay, I got them. I went with these partially because they included all the shift linkage, brake master, reservoir, line and even the caliper (though I won't be using that).

So where is the question in all this? The original brake system (of which I am retaining the caliper) used DOT 3 fluid. The new master and pipes require DOT 4. Am I wrong in thinking that I can take apart and flush the caliper (getting rid of all traces of DOT 3) and run with the DOT 4?

I assume someone out there knows more about this than me.

thanks
jason

[KGB]

yes you should be able to use DOT4.

It shouldn't hurt the lines.

[Boondocks]

Actually, you should be able to use DOT3 or DOT4. These fluids are made from the same base (Polyalkylene Glycol Ether) and are entirely compatible with each other. The DOT4 spec has higher boiling temperatures for dry (no water) and wet (3% water content) fluid. Under extreme braking conditions, when heat is transferred from the caliper to the brake fluid, DOT4 might give an advantage due to its higher boiling point. On the other hand, a racing DOT3 will outperform a normal DOT4 in dry boiling point.

The DOT4 was probably recommended as an extra margin for the brake caliper heat, although most disc brake systems spec either DOT3 or DOT4. It won't hurt the master cylinder to run DOT3, but DOT4 will work just as well and will be entirely compatible with your present setup.

Be sure to change the fluid at least every two years to prevent corrosion and gumming up of the master cylinder and caliper due to water absorption in the fluid.

[racerxnico]

cool,
I couldn't remember which one was silicon based versus the glycol based. Right after I posted I found something on line that spoke to 3 & 4 both being Glycol based, but it mentioned an additive in the 4 and wasn't clear as to whether they could be mixed.

I presumed they would be fine, but wanted to get another opinion before taking the next step.

thanks.
jason

[Steve]

The brake fluid that is Silicone-based is DOT 5.

To confuse things a bit further, there is also a DOT 5.1 that is glycol-compatible. Other than that, I don't know much about it.

You definitely DON'T want to mix DOT 5 with any of the others, and to convert to it, I believe you have to change some of the rubber parts. The little bit of improvement you might notice will be far offset by price and effort.