The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: mikebrisband on November 21, 2011, 08:29:35 PM
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Hi all,
I have re-bled my front brakes after a clean-out, drain and replenish exercise. I now have pressure but i notice that when I pull in the lever there seems to be a very small bubble of air pushing up within the master cylinder.
I spoke to the previous owner and he said it always did that, so i wanted to find out if this is normal or is there something else i should be looking at.
The brakes aren't spongy and they seem to have plenty of pressure, i just don't want to risk damaging anything or worse the brakes failing.
Any advice appreciated
thanks
Mike.
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There is a small hole that a jet of fluid will come out of when you release the brake lever .
If it doesn't do it, the hole is plugged and needs to be cleaned out .
It can cause a dragging brake, by not fully releasing the pressure in the brake system .
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The master cylinder most likely took a little air in the process of cleaning out the old fluid and now it's coming back out. Not a big deal. It'll eventually work its way out of there.
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try tying back your brake lever over night to rid yourself of the last of it.
Rev. Light
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I use that trick all the time! It's a good one.
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try tying back your brake lever over night to rid yourself of the last of it.
Rev. Light
+1000!!! I've had a couple bikes that were extremely difficult to bleed and I would give up, tie-wrap the lever overnight, and have a rock-hard lever the next morning.
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Yes always works for me too.
The interesting question is why does it work ?
Some say it allows the air to rise to the top but by what mechanism ? If it was that simple when you released the lever in the morning all the air would immediately bubble up into the master cylinder Does it actually do that ? I'm not so sure. Maybe someone could check.
What I think might happen is the air dissolves into the brake fluid firming up the lever but it then slowly comes out of solution again over a period of time. Where does it come out of solution ? At the lowest point of pressure in the system i.e. the point not under the head of fluid pressure which is the master cylinder.
Is it analogous to scuba divers and the bends where the nitrogen comes out of solution slowly or like opening a bottle of pop where it comes out fast ?
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Yeah, Barry, I know what you mean. It took me several years to finally try that methad since it wasn't logical. But once I did, and it worked, I was sold. But like you said, why???? Your explanation makes the most sense to me and I bet it is something like that.
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Hey thanks guys, much appreciated. I'll give the lever trick a go tomorrow. She's almost ready to get registered and start riding.
Thanks for all the help, really appreciate it.
PS: any R65ers in Brisbane, Aus?
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PS: any R65ers in Brisbane, Aus?
Not an R65, but there is a friend of mine in Nimbin. That's about as close as I know, I think. He is a regular on Boxerworks (MANY airheads in Oz on that forum!).
I remember reading about one near where the typhoon(?) hit a couple of years ago, north of you, I think?
Let me know if you want to get on our R65.org map:
http://maps.google.com/maps/ms?msid=209571359172950267307.000483701643b3f8becdc&msa=0&ll=-16.636192,144.316406&spn=85.122505,113.027344