Forum menu
Right, hopefully someone might have an answer for me.
I bought a set of XT brakes 2nd hand (very cheap) about 6 months ago. In the process of bleeding both before using them I noticed that the fluid in the front was almost black. Drained and replaced fluid. All worked perfectly.
After a recent lap of the Beast at CyB I noticed that the front lever needed a bleed again. Did so and noticed that the fluid was black again. Drained and replaced the fluid with the bleed.
When finished I left the bleed block in the caliper and the bleed nipple tightened up and pumped the lever whilst tapping the hose to bring any bubbles left in the system to the top. A couple of tiny bubbles came out, but also black contamination slowly rose up from the hole in the base of the reservoir.
Checked again the other day (about 3 weeks later) and the fluid is black again. In addition, just before the pads engage with the rotor, there's a noticable "clunk" like the pistons are getting caught on something.
So - what's causing the black stuff?
Is the contamination likely to be causing the issues at the pistons?
Would flushing the hose, lever and caliper with IPA (ie bleeding with IPA) clean all the crap out, or do I risk damaging seals that way?
Any advice appreciated!
Could the hose be extremely worn on the inside? swap the caliper with the rear one and see what happens.
I have noticed this myself when bleeding, although not to the extent you're reporting. All of shimano brakes I've had have had a touch of it. I put it down to a little bit of wear between the seals in the lever and master cylinder.
I would suggest draining all of the fluid from the brake (lever, hose + caliper) pumping some fluid through the lever to flush it out, then re-filling with fresh mineral oil and bleeding it thoroughly then repeating once more.
XT brakes can be a bit of a faff to bleed and get just so. I generally bleed them from the caliper up to the lever so the air rises with the fluid, then finish off with a little bleed from the lever down to the caliper to catch any air in the caliper.
NB When doing all this, make sure the caliper pistons are fully retracted to ensure as little fluid / air remains in the caliper.
Oh and the hose shouldnt wear / deteriorate at all internally.