Why change brake fluid ?

I am sure many of you guys already know this but to the rest, have you ever wondered why brake parts that are full of hydraulic oil get rusty and seize over time ?
The answer to this is that brake fluid is "hygroscopic" which means it absorbs moisture from the atmosphere, this is why brake fluid should be changed every two years (Complete flush which can be done by simply bleeding until enough fresh fluid has passed through to flush out the old) There are two main reasons why this is recommended,

Firstly the obvious corrosion issues, but more important is that when heat is generated (which is how a brake works) the moisture in the fluid can "boil" which creates tiny air bubbles from the steam which then make your brakes feel "spongy"

Very good reminder ! Thanks.
I'm the kind of guy that think....if it not broken, dont fix it. But having a 50 yo bike and not sure when was the last time that it was changed.....I'm adding this to my to do list.

I just looked in KZ900 Kawasaki manual and they recommand evrey year or 6000 km. 

I think a lot of the reason it gets ignored is that if you don't understand the "why" then you don't do it 

Here's what it turns into after sitting 10+ years

The shop manual recomdated brake fluid for my KZ900 is D.O.T. 3. and refert to specific brand. Like Shell super heavy duty, Texaco super heavy duty,  Castrol GT and other brand.

I found out on the web a good news...loll !  DOT 3 brake fluid will absorb less water than DOT 4 from the air over time, meaning you’ll need to have your fluid changed less frequently. DOT 4 brake fluid has higher dry and wet boiling points, making it safer for higher temperatures.

Modern bike seem to run (or stop) with  DOT 4, 5 or 5.1. 

Also, D.O.T. 5 should not be used unless the system has been completely rebuilt and is absolutely dry.

armorlubricants.com/blog/brake-fluids-differences/

Japan used to have crazy laws about vehicle maintenance requirements.  Cars, for example, at certain age limits, which were NOT very old, had to have all their brake lines and caliper/master seals replaced.  This sort of maintenance was so expensive, a lot of vehicles were scrapped at that point.  

Suzuki GS bikes call for replacing brake lines after two years.  Ha ha, nobody does that.  More like 40 years. 

On my Honda Civic, I bought an air pressure brake bleeding pump and master cap.  It's awesome.  You can bleed the brakes all by yourself in record time.  Great fun.  Too bad bikes don't have such adapter caps.  Maybe I should make one?  

Don't know if it will fit any KZ models.

www.kwick.biz/product/zrx-brake-bleeder-tool/

Nessism wrote:

Japan used to have crazy laws about vehicle maintenance requirements.  Cars, for example, at certain age limits, which were NOT very old, had to have all their brake lines and caliper/master seals replaced.  This sort of maintenance was so expensive, a lot of vehicles were scrapped at that point.  

Suzuki GS bikes call for replacing brake lines after two years.  Ha ha, nobody does that.  More like 40 years. 

On my Honda Civic, I bought an air pressure brake bleeding pump and master cap.  It's awesome.  You can bleed the brakes all by yourself in record time.  Great fun.  Too bad bikes don't have such adapter caps.  Maybe I should make one?  

This is doable Ed, I made one from a spare cap for my Harris many years ago (had a look earlier but can't find it to show you) the only thing I would say is keep the pressure super low (try 5psi) you don't want to re-do that stunning paint job

I gravity bleed mine every year.

Use a syringe to pull most (not all) of the fluid out of the master cylinder reservoir.
Then fill up with fresh fluid from a sealed container.
Attach a hose and container to the bleeder valve.
Open up the bleeder valve and let the fluid leak out.
Do not touch the brake lever.
Fill up the master cylinder reservoir as the fluid leaks out.
After a good amount of fluid in the bleeder container, I close the bleeder.
The cover is then placed back on the master cylinder.

There are refractometers that measure the water content of brake fluid.

This method is just used to replace the old fluid from a fully bled system.

A fully empty system is another story.