Why are my piston seals leaking and what to do?

[tommyboyo]

Two bikes, one with Ultegra calipers and one with Dura Ace.

Bikes were both left for a few weeks.

Came to ride the Ultegra and the brakes were squealing.

Did all the usual cleanups, re-bleed etc, etc. The front was now fine and has remained so, the rear seemed shot.

Replaced pads and rotor and bedded in the new setup.

All good. First ride, perfect. Second ride a bit of sqeal and reduced power. Third ride, basically no power and very noisy.

Did some research, checked the back of the pads where the plastic touches the pistons. Oily circles.

Checked the Dura Ace bike, same.

Assume seals are leaking?

Rear caliper only, so annoying.

Is that it for these calipers then, or anything that can be done and how/why did it happen when bikes were just sitting idle in a nice warm house?

[Noro]

Oh man, I would like to know it. I am just having the same issue but with my front brake Ultegra. I've changed the wheelset, so new rotors are in, I had to push the pistons with the pistol tool. Normal rubbing when installing the new rotors, bleed it out to have a fine break, went to sleep and the brake now goes all the way, bleed it again and in each bleed, I can hear like water splashing inside the fork, I am not sure. My pads were contaminated obviously so had to clean the whole setup again.

[tommyboyo]

Oh man, I would like to know it. I am just having the same issue but with my front brake Ultegra. I've changed the wheelset, so new rotors are in, I had to push the pistons with the pistol tool. Normal rubbing when installing the new rotors, bleed it out to have a fine break, went to sleep and the brake now goes all the way, bleed it again and in each bleed, I can hear like water splashing inside the fork, I am not sure. My pads were contaminated obviously so had to clean the whole setup again.

Something has gone wrong there mate.

A bit more than a micro leak at the seals for you I think!!

[PoorCyclist]

You can extend the pistons and clean it with alcohol and also check for cracks. If they are white they are made of ceramic.
After some use if there are still oil then you know you have a leak.

I normally apply a bit of mineral oil after cleaning, so I expect a tiny oily circle . That just makes the caliper work much better and less prone to sticky piston / uneven extension.

But I have seen a oily circle on my Juintech but not on my Shimano from factory, before I service them

In my case there is not enough oil to drip down get on the pads or loss of power, just an imprint. So I assume was oil from assembly.


Dura-Ace components should have 3 year warranty.

[tommyboyo]

You can extend the pistons and clean it with alcohol and also check for cracks. If they are white they are made of ceramic.
After some use if there are still oil then you know you have a leak.

I normally apply a bit of mineral oil after cleaning, so I expect a tiny oily circle . That just makes the caliper work much better and less prone to sticky piston / uneven extension.

But I have seen a oily circle on my Juintech but not on my Shimano from factory, before I service them

In my case there is not enough oil to drip down get on the pads or loss of power, just an imprint. So I assume was oil from assembly.


Dura-Ace components should have 3 year warranty.

Yes, I think I will get the Dura Ace caliper warrantied.

It is just such a pita swapping calipers and maybe then having to do the whole hose routing again if it is too short after cutting.

[kode54]

You can extend the pistons and clean it with alcohol and also check for cracks. If they are white they are made of ceramic.

Not sure they are made of ceramic which is brittle. I believe they are made from Teflon or Delrin.

[kode54]

You can put these stoppers in, clean the pistons with mineral oil and press them back in to see if some grit is causing the leak around the pistons.

https://www.instagram.com/p/CdoECxLrIn1/

These are 3D printed stoppers that allow you to push the pistons out to clean. Brilliant since they load from the top, not the bottom which makes it easier to use.

[rothwem]

You can extend the pistons and clean it with alcohol and also check for cracks. If they are white they are made of ceramic.

Not sure they are made of ceramic which is brittle. I believe they are made from Teflon or Delrin.

Pistons are definitely ceramic, the goal is to insulate the fluid from the heat of braking. I've got a buddy that has had his XTs and his Ultegras both warrantied for cracked pistons. Same symptoms as the op too.

[tommyboyo]

You can extend the pistons and clean it with alcohol and also check for cracks. If they are white they are made of ceramic.

Not sure they are made of ceramic which is brittle. I believe they are made from Teflon or Delrin.

Pistons are definitely ceramic, the goal is to insulate the fluid from the heat of braking. I've got a buddy that has had his XTs and his Ultegras both warrantied for cracked pistons. Same symptoms as the op too.

How would you tell cracked piston?

I have finessed them out for a clean up and all look in very good condition that are visible.

[MyM3Coupe]

Odd. . . I have none of these issues with my Dura Ace R9100 caliper brakes. Lolz.

[tommyboyo]

Odd. . . I have none of these issues with my Dura Ace R9100 caliper brakes. Lolz.

Great brakes, I have a set on one of my bikes.

Not relevant to this question though.

[Attermann]

It's fairly normal to have leaky pistons with shimano callipers, I had 2 with that, and my father the same, and that's with ultegra/xt the cheaper ones are even worse, 2 out of 4 had problems on my moms bike, and you always have same signs, squealing brakes, no power and a little ring of fluid on the back of the pads even thou it's dry outside

[tommyboyo]

It's fairly normal to have leaky pistons with shimano callipers, I had 2 with that, and my father the same, and that's with ultegra/xt the cheaper ones are even worse, 2 out of 4 had problems on my moms bike, and you always have same signs, squealing brakes, no power and a little ring of fluid on the back of the pads even thou it's dry outside

That's exactly what I have.

[Attermann]

New calliper it is, because shimano doesn't provide pistons and seals.

[tommyboyo]

New calliper it is, because shimano doesn't provide pistons and seals.

Pretty poor that this is 'fairly normal'!

I wonder if the next gen is better.