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Dirt Monkey
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282 Posts
Discussion Starter · #1 ·
I have been having some problems with my Shimano BR-M775 hydraulic disc brakes. I suspect the caliper and master cylinder seals are needing replacement. The brakes are very spongy even after bleeding, visibly seeping fluid at the calipers, and it takes a few pumps of the rear lever to get it up to pressure to work like it used to.

After doing a bit of research and finding the caliper/cylinder seals are not user serviceable I was a little disappointed. I don't have the cash to drop on a new set of brakes (or service) at the moment so I am looking for any info about the type of seals used.

Are the seals propitiatory in nature or just standard sized o-rings? I would think they are standard parts but I don't want to tear apart my somewhat functional brakes to find out until I have either solid info that they can be fixed with $1.00 worth of o-rings or enough cash to buy a new set of brakes.

A photo in this thread of a disassembled Shimano Saint lever (remarkably similar looking to the M775) shows what look like two o-rings for the master cylinder seals.
 

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5,451 Posts
The seals in the lever aren't just any ordinary o-ring, it has a lip on it.

Where exactly is it leaking in your setup? If its just the caliper, you can just buy another shimano caliper (no matter the model).
 

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Dirt Monkey
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282 Posts
Discussion Starter · #3 ·
Well that is disappointing news for the lever seals.

There is seeping around the pistons in both calipers and the seals in one lever are most likely bad because the lever must be pumped a couple of times to build pressure in the line. Would like to keep the calipers I have if possible since there probably isn't anything wrong with the body or piston. Seems like a waste to just throw it out because of a faulty seal.
 
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