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More of a curiosity this one. I bled my brakes today, and the first half of mineral oil that came out was a darkish grey colour. Kind of like puddle water. This is the bright red Shimano stuff.
What would cause this. High braking temperatures? Contamination? Something else?
Witchcraft.
Leaky piston probably or perished seals. I just got a new brake as no matter how many times I bled, it did nothing.
I think over time muck and water does get dragged past the seals.
From my experience that's pretty normal. One of the reasons you need to bleed them.
Bit of all there fella contamition and the o ring seals broken down a bit plus oil getting hot maybe not boiled but hot and mixed with the contimants, try a full flush though ride and then check in a month.
Peace out!
Mine are like this each time I bleed. Shimano.
My xt 785s have the grubbiest lever fluid I've ever had. It must be a function of their design. The calliper end always seems to be clean. I always push fluid in through the callipers before I bleed them to make sure I don't push crap into the system.
My suspicion is that the mineral oil pulls the carbon (black) out of the O-rings, seals, and possibly even small bits of aluminium off the cylinder bores (which then oxidizes and goes black)???
Funny enough I did mine today and thought the same!
Pretty normal then? They're not actually Shimano brakes. They're Tektro, but use the same mineral oil. Well, it looks the same. It's the same colour. It may have been mixed at some point, I honestly don't remember.
Every time I've done it in the past though, it's came out the same colour. Never seen it like that. But that said, they must be almost a decade old now, and it's the first time they've been done in a few years, if ever... Hopefully no leaks and they hold up.
I wouldn't usually worry about it but if they've not done it for 10 years and now they do, I'd be a bit less relaxed about that...
(my Oros on the commuter do it too, they're about 10 years old but they've always done it so it's not new behaviour)
Pretty normal for me, black gunge!
Northwind I emailed you about the headset , probably in the spam folder again!
I wouldn't usually worry about it but if they've not done it for 10 years and now they do, I'd be a bit less relaxed about that...
I had the same brake previously. They came with the bike, but one of them developed a badly leaking seal, so they got bled a lot (and it always came out red. They were also still relatively new). Until I eventually gave up and found the same brakes on eBay for not a lot of money.
These ones I'm honestly not even sure have ever been bled by me. They only get done if they really need it, and usually only small amounts.