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Discussion Starter · #1 ·
I addressed this subject in another thread, but I think it deserves separate attention. I just changed brake fluid on 2 of my bikes. I use electronic pen to identify the level of moisture in the fluid. I have couple of them. My previous fluid show red colour on the pen, not good. But see my surprise to notice that the brand new Brembo fluid had moisture in it, orange colour on the pen. On the other hand, the ATE brake fluid, which I think is one of the best in market both for heat resistance and longevity, had zero moisture after opening the bottle on numerous occasions. so my conclusion is that to discard the bottle after it is open is an old wives tale or simply a nonsense. additionally I am disappointed with Brembo. they make great brakes, but their fluid is of inferior quality. I throw the couple of bottles I got to the bin.

I am using one way nipple valve for bleeding, so no need to the complicated vacuum systems. it is a one man's job, so fast and so simple.

I am sure most of you know it, but it is good to tie a brake lever to the handlebar for the night, just to get rid of the little air that may be stuck there.
 

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Many neglect their brake fluid, going beyond the two year recommendation of most bike manufacturers. Some are needing a shorter interval, e.g., hydraulic clutches that see a lot of heat cycles. Do a full flush and bleed, then do a much quicker and easier bleed every spring at the beginning of riding season. This will virtually eliminate concerns with moisture and other issues with ABS systems, and will save you money in the long run. An ounce of prevention. Cheap insurance. DOT4, all you need.
 

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Discussion Starter · #3 ·
this is a sound advice, to flush the system once a year. but my point was that one can reuse brake fluid from a previously open bottle, no problem, if the bottle is properly sealed. and it is useful to have the electronic testing device. imagine my surprise when I discovered the the fluid from a new bottle had already moisture in it....! w..t..f.
 

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I've never quite understood the throw out the bottle once you've broken the seal mantra. Sounds like a recommendation from a brake fluid manufacturer. If the seal in the lid is intact then there is no way for it to absorb moisture through a plastic bottle once it closed. It it's left open for a long time then of course pitch it.
 

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In part full bottles of brake fluid, the moisture is in the air that takes up the rest of the space in the bottle, on top of the brake fluid. I guess if you could pour the remaining brake fluid into a smaller container that was full to the top you would extend its life. But why bother, its not worth the risk. I always find it amazing the ends we will go to save $ 4-5.00. Hell a coffee these days can cost that much. As always its your life and your bike, do with it what you wish, but be mindful of passing incorrect information onto the less informed. I can tell winter is coming.
 

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Discussion Starter · #6 · (Edited)
Yes, this is a. valid point; meaning about the possible effect of increasing the volume of air in the bottle. But I use very high quality ATE fluid which is not cheap here, not so easy to get, and comes in 1L metal containers. Throwing away 0.5L or more feels like a waste. And as I tested it with my electronic pen, the light was green, meaning zero water in the fluid. On the other hand, in the new unopened bottle of Brembo, the fluid showed orange color, which if I remember correctly is 1% or 2% of water. By the way, the fluid that I bled from the bike had 4% of water minimum, red color. I say minimum because the tester cannot show more. Red color means change the brake fluid now or Die :). And this was only after 1 year or riding. No wonder that my brakes felt less responsive these days. I will pay attention in the future to test the fluid more often

I know from storing liquid nicotine (I vape occasionally) that sucking air out of bottle increases its longevity, but this results from reducing oxidation, while here we speak about absorption of moisture from the air. Anyway, I trust my magical pen:). But I like the idea of transferring the fluid from one bottle to another so it is filled to the top.

I would think that brake fluids should be sold in metal containers, because the plastic is permeable and some moisture can migrate through the walls.


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In 1/2 liter of air at 50% humidity at 24C, there is about 6mg of water (6 uL = 6 cubic millimeter) (imagine the volume of 1/4" of a tooth pick).
Let's say that is spread in the 1/2 L of brake fluid in a liter bottle, over a season.

You might expose 5 mL of that old brake fluid (1% of the 500mL in the bottle) to heat high enough to boil water behind the caliper's piston.
So, 1% of our 6 uL of water = 0.06uL of water.
If this water expand at most by 1600x to vapor, it would become 96uL = ~0.1 mL = ~ bubble of 5.6mm diameter
Do that 4 times for the 4 pistons.

With this, you decide if those 4 BB sized bubbles are significant on your brake lever action...

Now the reality: you may never get even close to heating your brake fluid that much...

I've boiled the rear brake fluid once, going down a long mountain on dirt without abs (shy of using front brake). Not a fun minute...
 

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Discussion Starter · #8 · (Edited)
This is one very scientific explanation! It makes me think that it is a good idea to use brakes less aggressively and let the callipers cool down, after used too much, for instance by prioritising more engine braking at times. I used to in the past follow the procedure of bedding in the brake pads, according to EBC instructions, where for instance at one point at 100km/h you press the brake lever 8 times till the bike comes almost to a stop. The rotors were getting damm hot. I can only imagine what it did to the brake fluid!

I had very recently same experience with off-road bike. The rear brake faded to an extend that it simply stopped working; I had to wait for it too cool down. But this was the OEM brake fluid, so I replaced it now with ATE which has rather high boiling point.
 

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Discussion Starter · #9 ·
ok, just to share. I did an additional brake fluid testing, and I could detect a hint of water in the bottle that I opened like 6 months ago. Kind of similar as the new Brembo fluid I got. So I decided to fit ATE brand new brake fluid, just to be on the safe side. Anyway, it is not that the braking power improved dramatically, but rather the feel of the brakes. I changed the brake fluid on 5 bikes, including my friend's 300x, and the experience is the same. I don't know why the fluid absorbed so much water just in 1 year. Maybe because I have these bikes in Thailand and it is very humid here?
 
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