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I have a Shimano XT BR8100 system, all was good until I did some maintenance. Probably I did something wrong, trying to understand what. Did a normal procedure to replace oil and pump out air.

Visible problem is that they squeak at very high tone when I put medium to high push on a lever. And I see significantly reduced braking effect. In practice, I can't lock the front wheel with that.

I've tried to exchange front and back caliper, and the problem also swapped. This somehow shows the problem is in caliper/pads.

Purchased new pads just in case - does not help.

No visible oil leaks (or I don't know how to search for it).

Another funny evidence: As soon as you put some water on a braking disk and on a caliper - the issue gets fixed temporarily! Full power to lockout the wheel is restored, I can again easily lock the front wheel on any speed. And the screaming sound is also getting fixed (until the water dries out).

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    When working with brakes, cleanliness is most important. My guess (which is why this is a comment and not an answer) is that while replacing brake oil and getting the air out, some kind of contamination of brake disc/brake pads occurred. Only a minute amount of oil could cause this, might not even be visible to the eye. I suggest that you try to clean the pads and brake disc with brake cleaner, there are many guides on the Interwebz that is useful. To remove the wheel and brake pad and instead use a bleed block is good practice to avoid this.
    – MagnusK
    Sep 27, 2022 at 12:03
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    Oh, I forgot to ask: Does the brake lever feel soft/spongey or firm when braking? If soft feel, then there are more air trapped in the system somewere.
    – MagnusK
    Sep 27, 2022 at 12:07
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    On a theory of contamination - tried to clean disk with break cleaner, also tried to to handle pads with sandpaper. No visible improvement. I do suspect there could be some extra air. Its abit soft. Will try to follow official shimano bleeding procedure once again.
    – Igor
    Sep 27, 2022 at 19:02
  • Assuming you have the Shimano bleed cup, try doing a “mini bleed” . If that doesn’t work you might try a “gravity bleed” which goes top to bottom. The process for both are described online.
    – Warren Burton
    Sep 28, 2022 at 7:13
  • When you clean your disk and sand your pads you will need to bed them in again, no wonder the performance does not increase after cleaning. Also sanding is not always sufficient if the oil has creeped to deep into the pad.
    – reciprocal lettuce
    Sep 28, 2022 at 9:28

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Soo, answering my own question.

Tried:

  • sanding old pads, bed in - no result.
  • realigning caliper with disk (had to be done!) - but no help to the issue,
  • Mini bleeding procedure (had to be done, again) - no result

Finally, simply changing pads to the original Shimano j04c - fixed the problem immediately.

I think coincidence of two facts: oil contamination AND bad quality of replacement pads (“choose” something):

enter image description here

Conclusion: read the manuals and use genuine parts.

Those cool guys (ordered the same for the back breaks just in case):

enter image description here

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  • J04C work great and last a long time. Nice fix!
    – MaplePanda
    Oct 4, 2022 at 5:19

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