Brake Fluid -- Fact or Fiction?

[Coyote]

OK. The manuals all tell us that brake fluid is hydroscopic (absorbs water). I want to know how this can come in to play in a sealed system. They say brake fluid breaks down and should be replaced yearly or sooner. They say never use brake fluid from an open container. Just how worried should we all be about our brake fluid?
I probably shouldn't tell on myself. I filled and bled the front brake on my GS1000 18 YEARS ago. I haven't touched the system since, and the brake acts just like it did on day one. AND I am still using the original brake line. Stops on a dime.

Never use brake fluid from an open container. Just what exactly do they mean by open? I bought and put new fluid in my 550 cafe. I have enough left over the do another system I plan on using the fluid in my current 550 build when I get there. Essentially it's an open container, but was capped tightly after I used it the first time. How paranoid do I need to be? Do I run out and buy more and ignore what I already have? Oh, the things to ponder

So how long has YOUR brake fluid been in? Do you lie awake at night and worry how much water has dissolved in your system Or are you the type that changes brake fluid just because?

I guess what I'm trying to say is I think this all over played. Senseless hype.. Can anyone top my 18 years?

[Willie]

Here are my thoughts on this topic. Like yourself, I use brake fluid from a container which has been previously opened but tightly resealed. As with everything I'm writing, this all falls under the prefix IMHO. Moisture is not going to contaminate a can which hasn't been open longer than is needed to pour out what is needed and recapped. By "open container" I feel they mean one that has been opened and left opened. THAT brake fluid would be contaminated with moisture that had been absorbed from the relative humidity.
I try to change the brake fluid in my vehicles at least every 3-4 yrs. I consider it to be cheap insurance because its so easy.
I can imagine how brake fluid gets contaminated even in a brake system that is considered "closed". I imagine moisture gets in to the master cylinder reservoir through the vent. I can also imagine moisture getting in through the rubber seals in each caliper and possibly through the rubber lines, although that amount has to be infinitely small. My thoughts are based upon tests I conducted in Philip's R&D labs during the development of the video disc. Those tests consisted of determining if moisture can get through PMMA (aka acrylic plastic). I wasn't the only one that was surprised that acrylic is not a moisture barrier. I figure if moisture can get through 1/4" thick acrylic, it can get through the rubber parts in a brake system.
As for the brakes in your GS working just fine after 18 yrs, I don't find that surprising at all. A hydraulic system will "work" with any liquid. I would expect the bores of your calipers to be pitted and full of sludge after 18 yrs. They'll still work, no doubt, but not as good as they were when new.
Anyway, those are my thoughts and as I stated, they're all in my humble opinion.
Willie

[Suzsmokeyallan]

Never leave the container open longer than it needs to be. This keeps out unwanted dirt and those wandering moisture molecules.
Change rubber brake hoses at least every seven years or 60,000 miles. Your life really depends on it.
Flush brake fluid through the system with new fluid at least once a year. Fluid breaks down from heat and contamination.
Don't mix brake fluids such as silicone fluid to mineral etc. This can cause loss of braking power.

Seems simple enough.

[Craig380]

My 380 was restored by the PO in the early 90s. I did bleed the system through with fresh fluid shortly after I got the bike in 1999, just to be sure. I did it again a few years after that. Both times the old fluid was a bit dark compared with the fresh stuff.

Then around 2007 the caliper started sticking. I greased the pins, no difference. So I got a rebuild kit and tore it apart. The reason it was sticking was the chamber behind the piston was literally full of sludgy gunk. It had built up to the point that the piston could no longer retract properly.

These days I usually change the fluid every 3 years. I use a pipette to nearly empty the master cylinder, just leaving enough fluid to cover the holes, then add some fresh fluid and bleed the rest via the caliper nipple. This way, no air gets in the line and the whole job takes 20 minutes.

[yeadon_m]

+1 what Craig says. I'm a 2-3 year person also. My mileages are low on each of 4 bikes, but time is time I guess. The fluid does slowly darken anyway which is a kind of time clock.
Mike

[tz375]

I rarely change brake fluid, but I always rebuild calipers and master cylinder when I get a bike and use new braided lines when I get it.

After that it's a bit more of a crap shoot. On my RZ which is rarely ridden, it seemed to me that the brakes were not as good as I remembered, so off came the calipers for a clean. They were OK and not too much sludge, but the seals were a little sticky. A quick rebuild and flush through and bleeding and they were good as gold. Still not as good as the Phat Trakka which is what made me question them, but they should be OK for the next few years.

[GT750Battleship]

This is my number 1 job for January !!
it's been 2 years since a brake overhaul on my GT750,will do everything including new hoses
Cheers,
Roger

[2strokelove]

Yea for sure if you have 18 year old fluid, you will have 15 year old gung in there also.. And don't ever spill the stuff on your paint!!

[pull the wire]

I change mine seasonally on all my vehicles. DOT3 and DOT4 are "hygroscopic" which means it absorbs water very well. Even though we are told our brake systems are a sealed system, they must be vented slightly as to not create a vacuum in the system from expansion and contraction. The atmosphere and moisture will get in the vents, brake hoses, especially if they are old, caliper pistons and seals. Under heavy braking and lots of brake use, the fluid can get really hot. We've all made the mistake of: HEY I wonder how hot that rotor is and then touch it, YUP it's hot. DOT 3 has a dry boiling point of 400F and 284F wet. Dry meaning a new, un opened and recently manufactured. Wet meaning the fluid has been exposed to the atmosphere (2 years under normal use and riding or a 3 week old opened container). Wet also means it has a percentage of moisture in it no matter the percentage. If contaminated fluid gets only 72F over waters boiling point of 212F and boils, you will get air in the system and well we know what's gonna happen. DOT4 has slightly higher boiling points and absorbs moisture even better. I don't like blowing money on obsolete overpriced brake parts anymore. Bleeding the brakes and using new fluid from an un opened container is the only way to go IMHO.

[lrutt]

It's so easy to flush systems, why not.

When I rebuild a brake system I convert to dot5 as it's not hygroscopic.

On systems that have not been rebuilt though, I do flush every 5 years as SOP.