My brake fluid failed the moisture test already

[bradym-0101]

I changed my brake and clutch fluid only six months ago on my 749S, and I used a good local brand of DOT4. I carefully flushed and bled the system. But my new electronic tester, which workshops use, recently showed the moisture content was too high and it failed. So I did the whole job over again with Castrol DOT4. I even checked the new bottle right after opening it, and it already registered a small amount of moisture, though it passed the test.

This makes me think there must be a tiny bit of water in the air space inside the sealed bottle. Most people say to change street bike brake fluid every two or three years, maybe sooner in humid places. But if mine is failing in half a year, what am I doing wrong?

 

[redr1der]

my friend had the same problem with his 749s, try to check your master cylinder diaphragm and cap seal. if that rubber diaphragm is old, cracked, or not seating perfectly, your fluid is sucking up air (and moisture) much faster than it should be

 

[monstersp33d]

But my new electronic tester, which workshops use, recently showed the moisture content was too high and it failed.

this can be because of inaccurate readings from your electronic moisture tester. you need to
inspect all rubber seals, hoses, and master cylinder diaphragms for any signs of cracking, damage, or improper fitment. replace any components that are suspect
also verify the tester accuracy by using a chemical test strip

 

[MISTER DUCATI]

This is normal due to brake fluid being hygroscopic in nature (it naturally absorbs moisture)
This can be eliminated by isolating the brake lines that are near the exhaust system and engine.
Many of these models with ABS tend to overheat the brake fluid by being close to the exhaust, This end up by absorbing moisture in the brake systems and then this turns to air bubbles in the brake system resulting in a loss of brake pressure (soft brake pedal)

 

[Alan]

I've always thought changing fluid on bikes yearly and cars every two years is enough and use an extra high boiling point DOT4.

But good to know it's normal.