Moisture in brake fluid

[chuckycheese]

I know the general rule is that you shouldn't use brake fluid that's been in a closed but unsealed container for any length of time because of moisture absorption. Why not? After all, it can sit in the master cylinder of your car for, literally, years and preform just fine.

I asked an old dude at the parts store that question and he said he didn't believe it either. Any thoughts???

[Dave8338]

I think that if one uses a little common sense, and the fact that brake fluid now, all comes in a plastic containers, unless it's been rolling around in the trunk of your car for a few years, you're fine. Now, that being said, for the price of a new bottle of fluid, buy new unless you're in a pinch.

[Boondocks]

I know the general rule is that you shouldn't use brake fluid that's been in a closed but unsealed container for any length of time because of moisture absorption. Why not? After all, it can sit in the master cylinder of your car for, literally, years and preform just fine.

I asked an old dude at the parts store that question and he said he didn't believe it either. Any thoughts???

The longer brake fluid is in a master cylinder, the more it degrades and becomes contaminated. See Brake Fluid Does Wear Out.

[Mike McNaney]

How about switching over to DOT 5 and forget about it. No moisture absorption, wont crap up your paint if you spill it and wont boil to 500 Degrees.

Ive been using it in my 83' 1100E for almost three years with no problems.

[Steve]

Just because it's been in the master cylinder for years does not mean it's OK.

DOT 3 and DOT 4 fluids absorb moisture from the air, which changes their properties. It also changes their color, which makes it easier to tell when it is time to change. Moisture in the brake fluid will turn to steam if it gets hot enough, rendering your brakes virtually useless when hot.

DOT 5 fluid does not absorb moisture, but some say it is also not compatible with some of the rubber parts involved in the brake system. It is also not compatible with DOT 3 or DOT 4 fluids, so if you want to change, you should really disassemble your brake system TOTALLY, flush every single part, replace all the rubber parts, then put it all back together with new rubber parts that are compatible with DOT 5. Some might have gotten away with it and say they have had no problems, and that's great, but I would rather play it safe (and cheap) and just change the fluid every couple of years to keep it fresh. Only costs a couple of bucks for a bottle big enough to do the bike, so why not?


.

[Mike McNaney]

I dont know man...sounds like More scare tactics to avoid change. Same as "The synthetic motor oil makes my motor leak"
Old tech is old tech.
There are no compatability problems with M/C piston seals, boots or anything else rubber. Flushing with brake cleaner and a air hose and filling with $8 a pint DOT 5 gives a cheap performance and longetivity benefit in any brake system without ABS. Period.

$8 dollars a pint is not expensive. I consider it a real cheap performance upgrade.

[jeddininja]

I'm pretty sure the break system parts will be ok, but make sure you get all of the old break fluid out. I've heard that if you mix the two, they will combine to produce some sludge. key words are "i've heard".

better safe than sorry i guess.
my two cents.

k

[Nessism]

I dont know man...sounds like More scare tactics to avoid change. Same as "The synthetic motor oil makes my motor leak"
Old tech is old tech.
There are no compatability problems with M/C piston seals, boots or anything else rubber. Flushing with brake cleaner and a air hose and filling with $8 a pint DOT 5 gives a cheap performance and longetivity benefit in any brake system without ABS. Period.

$8 dollars a pint is not expensive. I consider it a real cheap performance upgrade.

DOT 5 fluids are iffy and have lots of drawbacks. This is a good read discussing the issues. http://www.xs11.com/tips/maintenance/maint1.shtml

My opinion is to stay with DOT 4 and be done with it.

Regarding the original question, I say to go ahead and use it as long as it's not more than a year old.

[rickt]

Here's the scoop from a chemist's point of view on the brake fluid issue. Dot 3/4 fluids are glycol based (an organic alcohol). Dot 5 fluid is a silicon based organic compound. Dot 3/4 fluid and Dot 5 fluid are not miscible which means that they don't mix (like oil and water). If you fill a brake system with Dot 5 that previously had Dot 3/4 and do not remove all traces of Dot 3/4, you will have "blobs" of Dot 5 fluid floating in the Dot 3/4 fluid. This is not a good thing! Dot 3/4 fluid is water miscible (it mixes with water). It is also hydroscopic meaning that it will pull water from the air. This is why it is always best to use an unopened container of Dot 3/4 fluid. As has been pointed out, water in the fluid is not healthy for your brake system. It lowers the boiling point of the fluid and probably more important, it will cause steel brake components to rust. When I open a new bottle of fluid and don't use all of it, I flush a blanket of argon gas from my MIG welder and quickly reseal the container. Nitrogen gas will work just as well. If you are considering converting from Dot 3/4 to Dot 5, I would suggest disassembling the entire brake system and cleaning everything thoroughly with denatured alcohol (this is basically methyl alcohol). Blow everything dry with compressed air and reassemble. There have been enless discussions about the relative merits of Dot 5 versus Dot 3/4. I have never been convinced that Dot 5 fluid when used in a properly prepared system will cause a problem. That being said, I use Dot 4 fluid in all four of my bikes. I change the fluid every year. I converted my classic car to Dot 5 fluid many years ago and have never had a problem.

rickt

[Boondocks]

I dont know man...sounds like More scare tactics to avoid change. Same as "The synthetic motor oil makes my motor leak"
Old tech is old tech.
There are no compatability problems with M/C piston seals, boots or anything else rubber. Flushing with brake cleaner and a air hose and filling with $8 a pint DOT 5 gives a cheap performance and longetivity benefit in any brake system without ABS. Period.

$8 dollars a pint is not expensive. I consider it a real cheap performance upgrade.

DOT 5 is not a performance upgrade, but a performance degradation. There are no scare tactics, just facts. No vehicle manufacturer recommends DOT 5 in its products. Harley Davidson doesn't even use it anymore. It is rarely used anymore for any use other than antique show vehicles. It will wear out your brake parts faster. It is two times more compressible and inferior to a good grade of glycol based DOT 3, 4, or 5.1 for general use.

DOT 5 is old tech, about 40 years old. Development of silicone based brake fluid was started in the late '60s for all-climate military requirements. Silicone brake fluid became available in the early 70's. A formula that met DOT 5 standards was set in the late '70s.

For facts about brake fluid, see the following links:

DOT 5

DOT 5 Silicone Brake Fluid Warning

DOT 3 Vs. DOT 5 Brake Fluid

Understanding Brake Fluid

[Mike McNaney]

Thanks for making my point. Theres nothing in any of those links that denies anything I said.
Maybe "spongyness", but I think that is subjective and dependant on the volume of fluid and types of lines.
My front brake lever has about an inch of travel total. Fine by me. Much better than stock. Im also a speed freak so I need no fade performance. Ive experienced, first hand what happens when your brake fluid boils when you really need it.

Hey, no foul use what you like, another point those links bring up is that it is really about preperation, use and the people behind the brakes.

[chuckycheese]

Interesting

I wasn't basing my observation on the moisture content of the brake fluid; I was basing it upon observed performance. Thanks for all the comments and the interesting information!