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· Banned Sock Puppet
17,903 Posts
Since you have to run the lines inside the frame and bars and cut to the correct length they have to be bled. You might be able to cut them and not lose any mineral oil but it's always best to bleed them to be sure.
Seriously, I have seen listings on eBay for Di2 disc groupsets that come "pre-bled". Granted there is no way those hoses will just happen to be the right length even if you are installing them on a bike that has all external routing. And no, I don't see how you could possibly cut a hose and not let some air into the system.
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