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Discussion Starter · #1 ·
I had my bike in storage for a long time, took it out about a year+ ago, and my mechanic completely rebuilt the master cylinder, among other things to get it running again. Everything been running great, no issues until a couple months ago... now whenever the bike sits for a couple weeks without riding, air is somehow getting into the front brake line. But no fluid leaking out anywhere. And only when the bike sits in the garage. I take it to my mechanic and he bleeds the air out (at the MC) and I'm on my way in under 2 minutes. This has happened twice. Now third time I bled it myself no problem, but can't get the bleeder valve closed. For some reason it will not budge, and my efforts have 'rounded' the hex shaped bleeder screw. I called my mechanic and he doesn't know what's causing the air to get into the line. He wants to replace the whole master cylinder ($210 + labor), but I'm looking for a less expensive fix, especially since we don't know for sure if that will fix it.

Does anyone know what might be causing air to get into the line or what I need to fix and/or replace? I spent an hour searching and combing through old posts on here, but didn't find anything anything specific to this problem that I was able to understand. A lot of good advice on bleeding the lines, but I got that part down already. Something about a banjo? Lol. Any help or advice is IMMENSELY appreciated. Cheers!

Sincerely,
An old AF vet riding a young man's bike, which is also old
 

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Use a rubber band to clamp the front brake lever and check after a few days to see if the lever has gotten closer to the bar and check for leaks.
 

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Discussion Starter · #3 ·
Use a rubber band to clamp the front brake lever and check after a few days to see if the lever has gotten closer to the bar and check for leaks.
I appreciate the reply and I will give this a try tonight, but I don't see how this applies to my problem. I read several posts where this was recommended, with a rubber band or zip tie, but how does this help me? I've already bled the air out and the brake is no longer mushy, it feels and tests normal. The problem is the bleed screw wont close, but the underlying problem is air somehow getting into the system.
 

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you mentioned that air gets in but you can't see fluid leaking out.
Putting some pressure on the brake lever over night might squeeze out the brake fluid so you could see a leak.
when I had some brake issues, I held the brake lever tight with velcro strip and next morning saw brake fluid coming out of the from calipers.

as for not being able to close the bleeder screw. So you have turned it clockwise and it's tight BUT when you squeeze the lever fluid comes out of the screw?
 

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Also, remove the bleed screw at the master cylinder to see if there is any corrosion at the mating junction. I suspect that after a few days you will see brake fluid leaking from a bleed screw or caliper piston.
 

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Discussion Starter · #6 ·
I've replaced the bleeder screw and bled the brakes (yesterday). Everything seems to be fine, brake feels normal. I forgot to leave a zip tie on the brake last night, but I'm going to take it for a test ride around the neighborhood in a minute and make sure it's good. I will put the zip tie on it when I get back and leave it overnight. Will report back tomorrow. Thanks!
 

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The seals in the front brake calipers need to be replaced I went through the same issue on my 2007 600rr which has the same brakes. I started with the MC just like you and after some time the brake lever would get soft again so after some research I found that the seals get old in the calipers and causes a loss in pressure. I bought a seal rebuild kit for 30 bucks online and never had another problem.
 
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