Shimano 8100 brake lever master cylinder leak?

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Shimano 8100 brake lever master cylinder leak?
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Posted: Apr 20, 2021 at 11:54 Quote
I have shimano M8100 levers with 8120 calipers (4-pot). I was bleeding my brakes and think I may have messed something up.

After bleeding brakes I noticed there was brake fluid weeping out of the end of the master cylinder. And I could notice bubbling from this same spot when I pulled the lever.

Eventually the leaking stopped. However next time I did a lever bleed on the brakes the leaking started again. The brake lever feels good and still seems to work fine, though it's not riding season here so haven't given it a really proper test. It does seem like the lever may get squishier as the fluid leaks out, not sure though.

Note, the leak is not coming from bleed port or the lever. It's coming from the round cap at the very end of the lever opposite side from the brake hose.

I think what may have happened is I was bleeding it and still had the plunger in the funnel while resetting the pistons. May have over pressurized system and blown a seal or something.

Anyone ever experience this? Any solutions? Know any suppliers with replacement levers still in stock? Lol.

Thank you.

Posted: Apr 21, 2021 at 6:32 Quote
You popped the bladder/diaphragm. I did the same thing on my 8120. Luckily the hole in the bladder was small enough that I just washed it clean of oil and used superglue to close the hole. You'll have to disassemble the lever to get to the bladder.

Posted: Apr 21, 2021 at 10:07 Quote
the-one1 wrote:
You popped the bladder/diaphragm. I did the same thing on my 8120. Luckily the hole in the bladder was small enough that I just washed it clean of oil and used superglue to close the hole. You'll have to disassemble the lever to get to the bladder.


Thank you. That is what I thought might have happened

How difficult is the process of taking apart the lever to get to the diaphragm and putting it back together?

Posted: Apr 22, 2021 at 17:22 Quote
The hardest part is putting the lever back on. Disassembly is easy. Reassembly is tricky because of the spring on the lever wanting to jump out. .

Refer to post #30 on how to remove the diaphragm cap:
https://www.mtbr.com/threads/2011-xtr-m985-brakes-leaking.750869/#post-11445009

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