brake oil kz650

I think the fluid is held air tight and not vented. You could take a master cylinder and hang it upside down and it wont leak. The vented part goes to the top of the rubber insert right below the cap. The master cylinder itself where the fluid is gets no air, but air is allowed on top of the rubber so it can expand and contract as brake fluid is drawn from the master cylinder. I think this is how they work anyways but I've been wrong more than once.

650ed wrote:

"The dot 5 does not absorb water so how are you going to get it in the system"

Condensation. The screw-on brake reservoir caps are not air tight. In fact, they are deliberately vented. Take a look at the threads inside the caps and (assuming your caps are like mine) you will find a channel cut perpendicularly through the threads that permits air to be exchanged between the reservoir and the atmosphere. I don't know if the later rectanglular type reservoirs are vented or not. I found that the round ones are vented when I built a pressure bleeder adapter for my bike. I had to plug the vent in my home-made adapter to get the reservoir to hold pressure. By the way, I've never had to rebuild or replace seals in any of my brake components. Ed

First problem with your thought, dot 5 does NOT absorb water so it will NOT collect water at the lowest point.
even if the system is exposed to condensation it does NOT absorb the water so it can not have a water issue at the bottom of the system.
the brake system is sealed as stated.
Since you have changed your dot 3 fluid out over the course of time you have removed the contamination in the brake system, which is a good thing, but if you had dot 5 in it you would not have to replace the fluid.
I am not wanting to start a bunch of crap but there is a better mouse trap in the brake fluid world, try it you will like it

Interesting article


DOT3 vs. DOT5

I suggest that anyone considering changing to DOT5 read Patton's link. I'm not trying to convert anyone who is happy with DOT 5, I just don't recommend it for the numerous reasons in Patton's link. Sorry, folks, it's not a better mouse trap. End of story. Ed

The article is not 100% correct, saying the fluid is constantly exposed to air. Isn't true, no part of the fluid ever is exposed to air. Like I said, that's the reason for the collapsable rubber part below your cap. Say you had 4 oz of brake fluid in the reservoir and your disc pads wore down enough to drain 1 oz of that fluid out. Like the artical says something has to give. What "gives" is the rubber is pulled down exactly 1 oz of volume giving you the 3 oz of fluid in your reservoir. The fact the top of the rubber is vented lets it collapse and expand with the changes in fluid volume. Air is not ever touching your brake fluid, so with this error in the writing of the artical, hard to say how accurate any of it's content is. You'll notice all hydraulic brake systems, whether they are on a car or motorcycle have this collapsable rubber system for this reason.

By the way, I've never had to rebuild or replace seals in any of my brake components. Ed

I have since rebuilt the rear (just cleaning and new seals), adding a GSXR master cylinder and resevoir, as that is what the GSXR system uses.

The only reason I rebuilt and replaced the seals in the rear caliper is because Dot 3 or 4 is NOT compatable with Dot 5. You cannot mix them. Therefore I cleaned out all the Dot 5 and replaced the seals.

I've never had to rebuild any of my calipers on any of my Kawasaki's either, even the high mile ones. I did have a leaky piston on the 78 KZ650 at the master cylinder and I replaced it after well over 100,000 miles. I had dot5 so no paint damage at all. When you think and read that the brake fluid is vented to the atmosphere, think of it logically. Why does the manufacturers stress so highly. Only use brake fluid out of a "sealed container". Because even a tightly closed partially used can of brake fluid may have possibly not been 100% air tight and moisture may have entered. They sure wouldn't say this if your brake fluid, once put in your master cylinder was constantly vented to the outside air which would make no sense at all.
As to the dot3 and dot5 not being compatable, although I'm sure this is true, all I did was pump out nearly all of the dot3, then add dot5, pump it nearly all the way out, add more dot5 ect, until I was sure dot5 was all that was being pumped out. This way no need to bleed the system or any other headaches. Does this get all the non compatable dot3 out completely? Must be good enough, because it's been 20 yrs and a lot of miles with zero problem

Post edited by: RonKZ650, at: 2007/09/25 13:10