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After a successful bleed of my rear caliper yesterday, I decided to do the front today. I went through the process, got all the air and old fluid out, sealed up the system, and when giving it the initial squeeze to check for firmness, the caliper popped. Oil spewed out, and now I can hear air coming in and of the system when I pull and release the lever. I'm so sad.

This is Deore XT, the M-8000 lever and caliper.

Questions that knowledgeable people will want to know the answers to...

Did I use DOT fluid instead of mineral oil? No, most definitely not. I used Finish Line brand mineral oil.

Did I pull the pads out? Yes, there was a bleed block in there when the caliper popped.

Did I squeeze super hard on the lever? Not really, I didn't really think about it. I've successfully bled brakes before and it was that that "initial squeeze" to see whether or not I need to continue trying to get air bubbles out.

Was the funnel still in the lever? No. I'd pulled it out and put the nut washer thingy back in.

Is there any chance the bleed nipple is still open a little bit? No...I checked it. It is firm.

So now I ask you, my trusted community? Did I do something wrong? Is this something that can be fixed? or am I looking at a new set of brakes? If it is fixable, how do I go about finding where it is leaking? Any other suggestions?

Best, Ben

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    What do you mean "caliper popped" Have you popped a piston - with a bleed block in place that is not likely, but the bleed block may have fallen out. If its a popped piston, reinstall it and bleed again (and make sure the bleed block stays in place).
    – mattnz
    Oct 29, 2020 at 4:07
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    So oil came spilling out of the caliper, but it's totally unclear where it came from? Oct 29, 2020 at 4:56
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    Was there a symptom that had you bleed it to begin with? You replaced all the fluid; was it heavily contaminated? Was there a lot of air in the system and if so did it get worse gradually or seemingly all of a sudden? Is this SLX M7000 or XT M8000? Have there been piston stickiness/retraction issues? Was the bleed block a normal yellow Shimano one? Oct 29, 2020 at 5:01
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    Oil from the caliper I think. although it could have been the connection at the hose. We may never know, I'm going to call LBS tomorrow, it may still be under warranty. The symptom was more in the rear...it was squishy and needed a bleed (that was the one I did yesterday.) The fluid was very dirty. Once I did the rear, it felt great, and the front was now the squishy one, although less so. I figured with the amount of dirty fluid in the rear, and the slight imballance in the levers, I would just do them both...as a pair. No symphoms other than that.
    – Ben Stokes
    Oct 29, 2020 at 6:39
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    Thanks, Maple. It may not come to that. I called the Bike shop that sold me the bike. He explained that although not common, sometimes the seals in the caliper can fail, but he would need to see it to be certain. It is probably covered under the warranty, which is 3 years for the XT line. I have perfectly sealed and functioning avid elixir that I have put on the bike temporarily.
    – Ben Stokes
    Oct 29, 2020 at 21:12

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Some Deore XT and XTR calipers have CERAMIC pistons, and if I remember correctly, that particular model has ceramic pistons.

And they have a nasty habit of cracking.

Take the caliper apart, and with compressed air thru the banjo port, pop the pistons. I bet you'll find a cracked piston.

As you know, Shimano does not sell brake parts. But Ali sells replacement piston kits.That's your best bet. Or, ditch it and get a replacement caliper.

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