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[quote="Molgrips"]Water maybe, with DOT, but how does air get in? you'd need negative pressure in the system. When the lever is released? That would hardly seem to be enough surely?You can't have water/moisture getting in without air getting in as well. Got to make your mind up. Its either sealed or not 😉
And it gets in with the dirt that gets in through the seals, it gets in through the reservoir (some comes back out out, not all), gets in through the hose connectors being wiggled and moved, or the banjos being moved/adjusted/knocked, the pistons being reset etc etc.
Yes, not all will get air in, it depends how they are used, fitted and cared for.
And FWIW the brakes on our race bikes used to get bled once a year, mine would always come out cleanish, just a little bit of discolouration in the stuff at the caliper end on the front. My other halves front brake would have a slug of black oil in the caliper. Despite doing the same races and very similar training.
Funnily enough, when the brakes were all swapped round, the black oil *still* ended up coming out of my other halves front brake, even though she had my rear brake caliper.........
And for the sake of an extra 20 minutes and 10 pence worth of oil per bike once a year when the bike is up on a stand being "dealt" with, i'll carry on bleeding brakes yearly...... (well, not on my hack bike, i'll keep that going until it breaks.)
What happens when you slip shortening the hoses on the new brake and then have to bleed them? do you bin those too?
Maybe I was a little harsh OP, and actually I'm in a similar position of needing to choose between sorting out some old Shimano brakes or just buying some cheap new ones...
I've got a set of XTR IS mount M965 Callipers attached to some M765 levers, they've worked fine for donkeys years with the odd bleed, the front should be fine with the PM-IS +20 mount I already own but the rear isn't going to fit the PM frame that I've now got, however I also have an old PM LX calliper from a previous bike which takes the same pads. So I could chop the Banjo end off the hose along with the XTR Calliper and fit the old LX, So I can still just about assemble a working set of brakes at near enough zero cost... But it is going to be a bit of a faff...
Alternatively I could just flog 'em and buy a set of cheap (but new) Clarks M2 for £40, I have to say I'm tempted despite the mixed reviews... Maybe I am a bit lazy after all...