Bubble??

[Fred1956]

Might be a silly question but I'm trying to wrap my head around it before I get to work on it....2013 EC300 with spongy front brake lever & poor braking. Short of time on Sat but I back bled it from caliper up and noticed what looked like a ball of water in the bottom of the master cylinder, turns out there is a clear 'dome' over the feed holes for the plunger & it was holding a big air bubble over the feed hole, but I couldn't figure out a way to get the bubble to float out... Any ideas? Anyone see this before? I tried to gently pry the 'dome' out but didn't want to be to rough as he had a race on Sunday. (Won the Pro class anyway) Advice or thoughts are appreciated. Thanks

 

[pscook]

Try inverting the master with the cover installed (don't want to spill). Or tip it with the cover removed and watch to see which way it has to go. Air always rises, so find the fluid path and let 'er have it.

 

[Jakobi]

I'll have a closer look at mine soon Fred. Its always felt somewhat spongey in comparison to my other bikes and you could be onto something. I bled it in both dirctions with little to no improvement. I have a banjo bolt here to replace the lighting switch so will check it out then.

Like Phil said, might need some physical manipulaton to get the bubble to slip out from where it is.

 

[Neil E.]

I cut a piece of clear lexan a bit larger than the master cyl and tapped a hole in the center. Threaded in a small tube fitting and connected that to a vacuum pump. Ran the pump for half an hour. Only way I could get the last few bubbles out. I swiveled the bars so the bubbles were sitting right at the bleed port.

 

[john r b]

Wouldn't a vacuume help in this situation ? Mity vac??