Brake Fluid
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Sorry for resurrecting this old thread. I just changed the brake fluid on my '07 VN900 for the second time (manual says to do it after each two years). The first time in '09 the brake fluid from both front and rear brakes bled out the same color as it was in the reservoirs. But this time in '11 it bled out clear from the front brake, but the first part of the bled fluid from the rear brake was discolored dark. Is there a reason for the dark discoloration of the fluid from the rear brake, and is it any cause for concern? I've not had this happen with any previous motorcycle. Many thanks.
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Usually dark fluid means that it was contaminated with moisture. Not the end of the world since brake fluid does attract moisture, but it's best to get it out. Could cause damage if left in there for a long period.
Maybe because the rear master cylinder is lower, it gets hit with splash from front tire? Guess that's why they say to change it every 2 years.
Maybe because the rear master cylinder is lower, it gets hit with splash from front tire? Guess that's why they say to change it every 2 years.
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Thanks, ricksza. If the discoloration was due to moisture, especially road splash, I'm puzzled about how it could have gotten into the rear brake hydraulic system past the seals. I've changed the fluid each two years per the manual. But it would be scarier if the fluid had gotten discolored because something in the rear brake system is disintegrating. The manual basically says to change the brake hoses and replace the rubber parts in the cylinders each four years, but that seems a bit much when I've had bikes for up to 20 years without changing anything in the braking systems apart from brake fluid, pads, and shoes.
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As much as everyone says that the system is sealed, moisture from air does get into the master cylinder. Some have vents, sometimes just from opening up the cap to check the level. Sometimes it gets introduced from an open brake fluid container. I would flush out the brake system and just keep an eye on it. Worry if it gets dark again quickly.
The color of the old fluid will also depend on how much/hard you've used the brakes throughout the year. When I do lots and lots of "spirited" mountain riding the fluid is darker than if I ride mostly interstate or straight/flat coastal areas.
To me discoloration has never been a cause for concern. And believe me I replaced some really, really dark brake fluid. Like coffee dark. Also I don't just replace the fluid but also make sure the reservoir is cleaned out. Sometimes I get a very fine residue settled in the bottom. Also- if it's been a particularly hard year overall for my brakes I'll replace the fluid yearly instead of waiting. Speedbleeders with a little tubing and an old coffee can make the job easy. They work fine with a hydraulic clutch fluid replacement too.
To me discoloration has never been a cause for concern. And believe me I replaced some really, really dark brake fluid. Like coffee dark. Also I don't just replace the fluid but also make sure the reservoir is cleaned out. Sometimes I get a very fine residue settled in the bottom. Also- if it's been a particularly hard year overall for my brakes I'll replace the fluid yearly instead of waiting. Speedbleeders with a little tubing and an old coffee can make the job easy. They work fine with a hydraulic clutch fluid replacement too.
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Many thanks for the responses, rbentnail and ricksza. Since I just flushed and changed the brake fluid last week I'll simply keep an eye on it. There was no residue in either of the reservoirs. I would not have been concerned at all except that in nearly 50 years of motorcycling the incident with my rear brake this time on my VN900 is the first experience I've had with discolored fluid.
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