I am about to replace my front brakes and I was doing research and read that dot 4 goes bad in a week after bottle is opened and it stay good in an unopened bottle for one year (What????). So how does it stay good in the master cylinder for a few years? Is the true or is this a Harley thing?

 

DOT 4 brake fluid is hygroscopic, (it absorbs water) and to keep your brake system performance at its best, should change every year. Shelf life of “opened container” brake fluid is also 1 year… buy a new 12 ounce can for your yearly change.

 

Thanks for the information. I figured the one week thing was wrong.

 

The MoCo recommends changing the brake fluid every two years.

How often fluids (engine oil, primary, tranny, brake) are changed is mostly a matter of personal preference.

 

I had a BMW front master cylinder go bad on my 1976 BMW R100RS. I had to pump the lever to get the brake to work.

When I took the master apart to rebuild, it was obvious rust and pitting was the cause. How did water get in there? Hygroscopic fluid, and my failure to change the fluid as required by the owner handbook.

I have been changing the brake fluid on schedule in my vehicles since 1979 or so.

 

How often fluids (engine oil, primary, tranny, brake) are changed is mostly a matter of personal preference.

You should place some value in the recommendation of "Roddenby" ...Look up "hygroscopic" and it might change your mind. Along with the moisture absorbed being corrosive, it also has a much lower compression and boiling point. When that moisture is boiled it evaporates which leads to air in the system.

 

I totally agree it should be changed at a period no longer than the MoCo's recommendation. Sooner is certainly fine. How much sooner? That can be debated ad nauseam.

I'm very well aware of the definition of 'hygroscopic'.

I stated that because of the myriad of "when should I change my ... fluid" threads. Regardless of the MoCo's recommendation, everyone changes it at their own period or mileage. roddenby is a perfect example. Therefore, it is a matter of personal comfort level or preference. As history has shown, when one individual changes their fluid has little effect on when someone else does. Is someone else going to change their brake fluid at 1 year because roddenby does?

There a several factors that are in play as to how quickly brake fluid absorbs moisture and should be changed. The climate for one. Riders in a high humidity climate (south Florida) should change it more often than those in a drier climate (central Texas). Type of brake lines, how often master cover is removed, brake wear requiring addition of fluid, use of old brake fluid, etc.

 

I think that maybe you read too much into my statement? In no way was I suggesting that you were ignorant as to the importance of maintenance ... :>)

 

Sure, you say that now... JK

It wasn't taken that way. I just read too much into it.

I hope you can fend off old man winter a bit longer in your neck of the woods. Ride safe Larry.

 

Here is how to make sure after opening that it will last a year.

Just put a pin hole in the seal after removing the cap. It also will pour with more control and no spills. Tape the pin hole and put the cap back on.

This has worked for me since the beginning of time and I'm 75.

I go by the color of the fluid and not the time limit. The clear fluid turns brown with time. The oldest fluid that I changed was DOT 5 in a 2000 Deuce last winter after 15 years. i converted it to DOT 4 by thoroughly pulling out all fluid in each system with a vacuum pump and then flushing thee times with Dot 4. Worked great. You should see what the first flush of DOT 5 looks like when DOT 4 is introduced. The mix turns to snot like rubber jell.

AI did it because somewhere in the past 10 years HD changed from DOT 5 to DOT 4. It is harder in this rural area to get DOT 5. This way with 18 bikes I only need one supply.