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While bleeding my Shimano 105 hydraulic rear disk brake (BR-R7070) the seal around one of the caliper pistons failed.

I was following the Shimano dealer manual meticulously and I had only just done the front brakes with no trouble so I'm surprised to have a failure on the rear.

I suspect it is because the genuine Shimano bleed spacer didn't fit all the way into the break caliper and hence there may have been unequal pressure across pistons when applying pressure to release any air bubbles from the lever. This appears to have made one piston jam in an uneven position.

Has anyone else encountered this issue? Can I repair the caliper or should I just buy a new one?

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    FYI if the spacer doesn't fit, it isn't being used properly! However, you can salvage this situation without a new caliper.
    – Noise
    Oct 17, 2023 at 9:03

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It's very likely the root issue is damage to the ceramic pistons. Caliper seal issues on ceramic pistons Shimano brakes almost always are.

Genuine replacements are not available, though third party ones may be. I would recommend replacing the caliper, hopefully via warranty.

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  • Thanks Nathan, given the importance of brakes I’ll replace the caliper with a genuine replacement part. I’ll further investigate why the Shimano branded bleed block doesn’t fit properly to see if it’s a problem with the tool or the way I’m using it.
    – Brad
    Oct 18, 2023 at 17:35

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