A Word to the Wise: Bleed/Change Old Brake Fluid! - Chicagoland Sportbikes
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post #1 of 2 (permalink) Old 06-13-2005, 05:47 AM Thread Starter
Must... brake... later...
mikdivad's Avatar
Join Date: Apr 2002
Location: Irving Park
Posts: 478
Location: Irving Park
Sportbike: 2008 Yamaha R6 in Race Trim
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A Word to the Wise: Bleed/Change Old Brake Fluid!

Just wanted to share an incident that occurred at the track this past Saturday.

As I was going through tech inspection, the Nesba instructor looked at my brake fluid and advised me to change it soon since it looked pretty dirty. I had changed the brake fluid about 1 year ago to some racing fluid, and was actually planning on changing it sometime this week. I figured it would be alright for one more day at the track though. Boy was I wrong!

The first session out I was getting comfortable, and started to pick up the pace about mid-session. At the end of the back straight, I passed Paul from Polar-Optics on his inside intending to brake a little deeper to pass him. After I completed the pass I pulled in my front brake lever... and NOTHING HAPPENED! No brakes! So I did what I was taught to do, which was pump the lever until fluid came in. Well fortunately the fluid did come back in and in my efforts to pump, I locked up the front tire. After about a few feet of having my front tire begin sliding out from under me, I realized what was happening and let go of the lever to go coasting off of the track. Saved that one, but just barely.

I got back in the pits and went to apologize and explain what had happened to Paul. We then proceeded to diagnose the problem. He first asked if I had a tankslapper which might have pushed the pads back, but I didn't. Then he asked how old my brake fluid was. When he heard it was a year old, he immediately went for a cup with a small hose attached that looked like it was for a urine sample. "Bleed your brakes! I'll bet you'll find an air bubble." Sure enough I did, even though Vcook and I were really careful when we put the new fluid in a year ago about getting all the air bubbles out. Evidently brake fluid is water soluble and begins picking up moisture through time, which can lead to expansion and air bubbles at very inopportune moments. I never had this problem before, but luckily it didn't lead to anything more serious than a loaded pair of underwear.

So the moral of the story: Change your brake fluid every year and be sure to bleed out all the air bubbles. Nothing worse than pulling in that lever and having nothing happen.

I have an appt. with Vcook this week as soon as he is available.
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post #2 of 2 (permalink) Old 06-13-2005, 07:07 AM
Got my new Ride......
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Join Date: Sep 2002
Location: Naperville, IL
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Location: Naperville, IL
Sportbike: YZ250, GSX-R750 K1, ZX-7R (RIP)
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Good Info !!

And even if you think you got all the air bubbles out when changing the fluid, its always a good idea to bleed them again from time to time to make sure all is good. As the fluid picks up moisture & contaminants, it will BOIL easier. If you manage to boil it slightly - you will obviosly have more air/vapor in there. This can cause vapor-lock ==> which means fluid is in such bad shape that it boils enough to fill the chamber with a significant amount of compressable vapors -then it will feel like you almost no brakes !!!

- Sam
NESBA #749
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