Where's all this air coming from?

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Where's all this air coming from?

Postby Guest » Sat May 13, 2006 4:01 pm

The brakes on my 650Z have never been very good, when I got the m/c one caliper was siezed so I replaced the body and piston, and rebuilt the other with new piston and seals, but the brakes were spongey despite lots of bleeding, since then I've replaced the master cylinder and added s/s brake lines but no matter how much I bleed, the lever does not become firm, when the bleed valve is cracked open should the fluid come out like a jet when the lever is sqeezed? mine doesn't just dribbles, and there seems to be more air in the system than fluid, where can air be entering the system, looking forward to any comments.

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Ibsen
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Postby Ibsen » Sat May 13, 2006 6:28 pm

Try this: pull the brake lever and strap it to the handlebar. Then open the cover on the master cylinder slightly. Let the bike sit like that over night. That usually helps.
What happens sometimes is that there will be a lot of small airbubbles in the brake fluid, and they won't come out by bleeding the brakes. By strapping the lever and keeping the pressure constant, the air bubbles will rise to the highest point, the master cylinder, and finally disappear.
Last edited by Ibsen on Sun May 14, 2006 2:29 am, edited 1 time in total.

fishtoft
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Postby fishtoft » Sat May 13, 2006 7:21 pm

Forgot to log in when I started this topic, the lever is strapped back as you suggested,will let you know the result, thanks

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Vatch
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Postby Vatch » Mon May 15, 2006 10:25 am

I had problems like this when I rebuilt my brakes. I took a more physical approach to getting the air bubbles out. With res cap off so you can see turn turn the handlebars hard to the left and slowly open and close lever about five times. Turn handlebars hard to the right and repeat. I would intermittently lightly tap the lines and mechanisms with a rubber mallet. CAUTION: you'll need to remove some of the brake fluid from the res or you'll have it all over the place. I did this after leaving the lever pulled over night and I couldn't believe how many tiny air bubles kept coming out. I did this for about 2.5 hours total at 30 min intervals over 2 or 3 days until I saw no more bubbles and I had pressure. Then I topped off the res. I took a while, but it worked.
'99 1500 Drifter

fishtoft
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Location: boston england

Postby fishtoft » Mon May 15, 2006 5:33 pm

many thanks for the responses, I seems the trouble was with the right hand caliper, dont ask me why but when I removed the hydraulic line and plugged it with a nut and bolt the lever was solid. I dismantled the caliper and believe I might have left the old 'O' ring in, so I found the 'new' one in the parts tray, fitted it and now good as new! What surprises me is that although it drew in air, it didn't leak fluid. Thanks again.

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Ibsen
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Postby Ibsen » Wed May 17, 2006 10:52 am

Glad you got it sorted out. :D


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