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Discussion Starter · #1 ·
*bike is a K8 750 (R6 Master Cylinder (rebuilt), new pads, rebuilt calipers, Galfer S/S Lines with new hardware/crush washers, torqued to spec)

I'm having some issues with what I can only assume is air trapped somewhere in my front brakes after installing new s/s lines. Brakes are "good" but a bit spongy (I have an identical braking system installed on another bike. Lever feel is rock solid - absolutely no "sponge" at all)

I've tried removing each caliper and pushing the pistons back in (saw no bubbles), I've hung the calipers high over night (to let any air bubbles rise) and I've tied my brake lever to the bar over night (and most of the other little "tips and tricks" you read about). There are no bubbles coming out at all, fluid level remains the same and I see no leaks anywhere.

After unsuccessfully trying "everything else" (several times), I am trying to do a reverse bleed, which has always worked beautifully for me in the past. However, this time I am unable to push fluid into the calipers (any of them). I have a good syringe/hose set up, but when I open the bleed nipple, no matter how hard I push, the fluid will NOT go in.

In 30+ years of wrenching my own bikes (replacing lines has been one of the first things I've done to every bike I've owned), this is a first for me and it's driving me nuts lol. Any ideas or suggestions?
 

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If you raise the calipers that would make the air bubbles go to the caliper and not escape. So just standard bleeding should be fine. Try bleeding at the lever too. If there is in fact no air in the line and its still spongy then I would ditch the rebuilt stock r6 master cylinder and go with something new aftermarket.
 

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Discussion Starter · #3 ·
If you raise the calipers that would make the air bubbles go to the caliper and not escape. So just standard bleeding should be fine. Try bleeding at the lever too. If there is in fact no air in the line and its still spongy then I would ditch the rebuilt stock r6 master cylinder and go with something new aftermarket.
Thanks for the input! When I raised the calipers, I bled at the caliper while they were still elevated (with an old disc between the pads) - so any trapped air should have burped out. I've bled the lever/master several times (standard way) and I get no bubbles....So it's very odd. I'd be open to replacing the m/c, but would rather rule out anything else first. I only rebuilt the m/c as part of regular maintenance (prior to changing the lines) and it was working beautifully. The fact that I can't get fluid into the system using the reverse bleed is the real puzzling thing.....
 

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You did open the bleeder on top when you tried to push fluid in the bottom? If it had no where to go, it won't go in?
 

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Discussion Starter · #5 ·
You did open the bleeder on top when you tried to push fluid in the bottom? If it had no where to go, it won't go in?
Thanks. Yes, I did it with bleeder open (and just for the heck of it, I've tried it closed and combinations of open/closed with lever out and pulled in) 🥴
 
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