That has happened to me twice. First I was careless when pressing the pistons back before bleeding. Next time I was using the official bleed block that is slightly undersize and doesn't support the piston fully. I wanted to get good bleed and realy squished the brake lever during one bleeding step. The piston didn't move after that (I rode it like this and went over bars because of lack of modulation). When I disassembled the caliper the piston was broken from inside exactlh like yours.

 

Now you mention it I use an unofficial bleed block which is the same. I can hear the pistons contacting the bleed block as I squeeze the lever and it doesn't quite line up or support the whole piston fully. I'd not considered that possibility but suppose it could be well be the cause. Thanks for your input @arnea I appreciate it. 👍

 

I had the same exact thing happen with a XT that I bought back in 18'. One side wouldn't retract, so I pulled the pads out and got to poking around. This led to me pulling the caliper apart to find that one of the pistons had shattered on the back side. I figured since I'd already disassembled the brake, a warranty was out of the question, so I bought some aftermarket pistons off of Amazon. Ultimately figured out that the caliper had a casting flaw and ended up replacing it.

 

Yeah I couldn't actually get the caliper in half like I did with my old M7000 version, the two torx bolts we're really locked into place so I didn't want to force them for fear of stripping the heads.

I managed to eject the piston by flushing water through from the bleed nipple. I did have a really good look at the inside of the caliper bore and the seal while it was out and didn't notice anything unusual or damage to the seal luckily but it could be possible there is an imperfection somehow.

I've looked at those aftermarket (Z Power?) pistons on ebay but never thought of trying them but worth keeping in mind for the future.

I'll keep an eye on the caliper for a while and if there's any sign of it happening again I'll replace for new just in case. Thanks for your input also @DoctorJD. ??

Thank you for all the help and feedback, this one really had me guessing as I've never heard or seen this happen before. ??

 

I have seen this before and its not an uncommon problem from pad spreading and getting the puck slight cammed and fracturing the inboard edge just like yours. Yours is the worst I've seen though.

 

Yeah that makes a lot of sense C2L. I have messed around with them a couple of times recently for various reasons so there's been more chance of damage than usual.

Maybe I've cracked it slightly initially without noticing and just made it worse. Thanks for the help Buddy, seems like a viable reasons it happened and why it's so bad.

Hoping I won't need to go near the caliper from now on but I reckon a lot more care is needed if I do. ??

 

That problem is quite common and old with Shimano's ceramic pistons.
You don't even need to bleed you brakes for it to happen. And it's another reason why some have switched to Magura calipers.

Here is a tip for you. Flush your whole hoses real good before installing new calipers, or pistons.
If tiny ceramic particle are still inside, your new pistons will crack pretty fast again.

 

That problem is quite common and old with Shimano's ceramic pistons.
You don't even need to bleed you brakes for it to happen. And it's another reason why some have switched to Magura calipers.

Here is a tip for you. Flush your whole hoses real good before installing new calipers, or pistons.
If tiny ceramic particle are still inside, your new pistons will crack pretty fast again.

It's been an eye opener that this is so common. In my mind any damage is to the outside of pistons from using metal tools to retract. I assumed the inside of pistons are protected from any kind of damage, obviously not.

Besides a few substantial shards there was a lot of almost ceramic dust in the bore. I flushed out the caliper with around 10 syringes of water and left it to dry out.

Thanks for the tip, that's something I'd not considered until now @OneTrustMan. I'll do a gravity bleed when I get chance as there is likely to be particles in the hoses. 😎🤙

 

Sometimes old school is the best. What is the risk vs. reward.
MTBs run in harsh gritty sandy conditions therefore ceramic would be more prone to abrasion is my guess.

@Reaper...Did you use a microscope for those close up pics 😁😁

 

Sometimes old school is the best. What is the risk vs. reward.
MTBs run in harsh gritty sandy conditions therefore ceramic would be more prone to abrasion is my guess.

@Reaper...Did you use a microscope for those close up pics ??

Hey Buddy, ? nice of you to chime in at last! I used to think it's cool having ceramic pistons, not any more.

I'm now considering those aftermarket piston kits in future. I do love my SLX's and needed a bit more braking power but have to admit my old set of bog standard Shimano's worked flawlessly for years.

My mobile camera did have trouble with the auto focus trying to get those pics. Thanks for your input @speeder2. ??

 

Think ceramic bearings

 

No chance C2L! 🤣 The least amount of ceramic parts on my bike the better after this!

 

Okay, no worries, thanks Buddy. I'll do the research before buying anything as usual.

Either way I've wanted a 4 pot on the front for a while and it's good to know there are replacement resin pistons available.

 

I will chime in on ceramic pucks. I prolly misstated my take on the commonality of seeing fractured pucks. It has been seen multiple times, but I do not feel this is a common problem. I have run Shimano brakes on all of my bikes for 15 years and never have I experienced this on my brakes. I have helped friends and observed acquaintances that have cammed the puck when not keeping focus on squarely and slowly pressing it into the caliper.

Ceramic pucks are delicate and easy to fracture if mishandled. From a maintenance perspective, it's not a difficult task, but I think the attention these sometimes need get overlooked and we see a broken puck.

Think again about replacing the ceramic pucks. Ceramic serves as a thermal barrier between the pads and brake fluid and reduce the heat transfer to the fluid. That's the primary reason for their existence.

 

Check out Deore calipers, I believe they are not using ceramic pistons. Functionally the same as the other models, even come in 4 pistons.

 

Which ones?
The M6100 do have ceramic pistons.
I know that because my new bike came with them.

 

I've only had Shimano brakes, what do other brands use? Never had an issue with cracked pistons but that's just a few sets of brakes.

After a single ride with a lot of hard downhills my brake fluid starts turning black indicating there's a ton of heat making its way to the fluid. I have no idea what temp that would be but I'd be worried about the thermal conductivity of anything besides ceramic transferring heat to the brake fluid.

 

Older gen deores, didn't look at the recent 6xxx yet.

 

Stay on sidewalks and there will be no problems.

 

Fwiw I'll be choosing the SLX M7120 caliper for the front for no better reason than for it to match the M7100 on the rear and keep my whole bike with SLX components. 😉 Not looked into exactly what type of pistons in the newer SLX's yet but not too fussed.

Based on the latest posts and helpful info, probably won't consider Aliexpress replacements as an option reallistically.

Nothing against ceramic pistons as besides this one issue I've never had a problem. I'll put this down to not treating caliper carefully enough and heavy handed user error during maintenance.

I've learned my lesson and will be very gentle when dealing with these fragile piston in future. 😎

 

If I were a downhill rider...I would borrow ideas from moto industry.

Largest rear rotor and pads plus thickest steel braided lines.
Then I would run a bottle to hold more fluid at the back...connect small container with hose from the front going in and then a hose going out to the rear brakes.
By adding fluid there and this setup will allow the brake fluid to cool faster and absorb heat. It will take the heat from the pads and move them along the steel lines and into the metal container holding cooler fluid. Plus you will also have more force and stopping power because you have more volume of brake fluid.
I noticed the minor difference how my rear brakes need to be pulled/pumped more before it gets stiff where as my front brake is stiff. I did this test on 2 identical bikes.

Try this and you will remove the air from you lines plus make them firm.
use velcro or zip ties or string...pull your brakes in as far as you can and tie them off.
Leave for 24 hours or 48 hours.
Once in a tap on the master and lines and pad calipers...this will help release any air bubbles.
After 24 hours your levers will be hard...great for 1 finger braking.
If you are careful, move your master horizontal and gently open the filler cap on master (without levers pulled in).
Have some fluid/oil ready to drop in even baby oil for Shimano system.
Have a clean tiny 2mm allen key or blunt object. Pull in the brake lever just a tiny bit, slowly and keep going until fluid comes up to the top (okay if it goes over).
Now insert the allen key to the bottom and move it a bit. Remove the key, tap on the master...slowly release lever BUT get ready to add fluid as it is sucking in...just add it a few drops...do this about 3 times. At the end you want that fluid at the top therefore when you screw back down master fill/bleed screw, a bit of fluid will come out/over.
After you do this also, zip tie the levers for 24 hours.

You now have brake lines and master with no air and max fluid...brakes will be rock hard and should be NO FADE.

I have been using a good baby mineral oil and working fine. Seth did this test after a year and said no difference vs. Shimano mineral oil.
Check Youtube for Seth's bike hacks.

Always have a rag under the areas especially with DOT.
Also, stop believe the BS about touching your rotors.
Just clean both sides with rubbing alcohol or better brake cleaner...spray on a rag then wipe the rotors real good.
It's a good idea to remove the wheels and clean rotors and ALSO clean the brake pads.

Do this and your braking system will be solid or you will discover you have issues because your levers are soft or you keep seeing air bubbles.
Simple trick for removing air...get something that vibrates (electric toothbrush, shaver, sander etc...) and place it against your calipers for a minute and then along the lines and finally at the master cylinder. This will force the air bubbles up and out. Try to have someone do that while you have the master screw off and looking at the bubbles come up and inserting the object to release the bubbles inside (you are popping the internal bubble in the master).

Do this once, should take you about 30 minutes for both brakes...you are done for the year or until you change your DOT fluid next year.
Please provide all donations and tips to Reaper as he has helped me TREMENDOUSLY with other aspects of by bikes and gear.

I am new here, maybe someone can get this pinned.


Many of you have air in the lines.
Also if you are using SRAM or DOT brake fluid, you have another problem.
DOT fluid is hydroscopic meaning it absorbs moisture over time. In moto world we change our brake fluid at least once per year.

 

If I were a downhill rider...I would borrow ideas from moto industry.

Largest rear rotor and pads plus thickest steel braided lines.
Then I would run a bottle to hold more fluid at the back...connect small container with hose from the front going in and then a hose going out to the rear brakes.
By adding fluid there and this setup will allow the brake fluid to cool faster and absorb heat. It will take the heat from the pads and move them along the steel lines and into the metal container holding cooler fluid. Plus you will also have more force and stopping power because you have more volume of brake fluid.
I noticed the minor difference how my rear brakes need to be pulled/pumped more before it gets stiff where as my front brake is stiff. I did this test on 2 identical bikes.

Try this and you will remove the air from you lines plus make them firm.
use velcro or zip ties or string...pull your brakes in as far as you can and tie them off.
Leave for 24 hours or 48 hours.
Once in a tap on the master and lines and pad calipers...this will help release any air bubbles.
After 24 hours your levers will be hard...great for 1 finger braking.
If you are careful, move your master horizontal and gently open the filler cap on master (without levers pulled in).
Have some fluid/oil ready to drop in even baby oil for Shimano system.
Have a clean tiny 2mm allen key or blunt object. Pull in the brake lever just a tiny bit, slowly and keep going until fluid comes up to the top (okay if it goes over).
Now insert the allen key to the bottom and move it a bit. Remove the key, tap on the master...slowly release lever BUT get ready to add fluid as it is sucking in...just add it a few drops...do this about 3 times. At the end you want that fluid at the top therefore when you screw back down master fill/bleed screw, a bit of fluid will come out/over.
After you do this also, zip tie the levers for 24 hours.

You now have brake lines and master with no air and max fluid...brakes will be rock hard and should be NO FADE.

I have been using a good baby mineral oil and working fine. Seth did this test after a year and said no difference vs. Shimano mineral oil.
Check Youtube for Seth's bike hacks.

Always have a rag under the areas especially with DOT.
Also, stop believe the BS about touching your rotors.
Just clean both sides with rubbing alcohol or better brake cleaner...spray on a rag then wipe the rotors real good.
It's a good idea to remove the wheels and clean rotors and ALSO clean the brake pads.

Do this and your braking system will be solid or you will discover you have issues because your levers are soft or you keep seeing air bubbles.
Simple trick for removing air...get something that vibrates (electric toothbrush, shaver, sander etc...) and place it against your calipers for a minute and then along the lines and finally at the master cylinder. This will force the air bubbles up and out. Try to have someone do that while you have the master screw off and looking at the bubbles come up and inserting the object to release the bubbles inside (you are popping the internal bubble in the master).

Do this once, should take you about 30 minutes for both brakes...you are done for the year or until you change your DOT fluid next year.
Please provide all donations and tips to Reaper as he has helped me TREMENDOUSLY with other aspects of by bikes and gear.

I am new here, maybe someone can get this pinned.

Many of you have air in the lines.
Also if you are using SRAM or DOT brake fluid, you have another problem.
DOT fluid is hydroscopic meaning it absorbs moisture over time. In moto world we change our brake fluid at least once per year.

What does any of that have to do with shattered ceramic pistons?

 

Sounds like a trolling party

 

.

 

@Reaperactual
That dude got the china pistons, but only replaced the 1 broken piston.

 

That clip helped in a way @OneTrustMan. Got me thinking how close I'd come. Pad was almost totally worn out, so close to fluid squirting out, contamination and maybe even complete, instant brake failure? That's a scary thought.😬

 

🤣 @OneTrustMan, urmm, don't think I'll watch out for any more of that guys 'tutorials' or listen to any of his advice in future.

That guys paid almost as much for those Chinese pistons than I paid for my original whole pre bled M7000 rear brake! £35 on sale from Wiggle UK! 💰The reason it was so cheap was they sold it as a 'continental set up' left hand front, took 5 minutes to sort that out!😎

 

As others say, the broken piston is caused by operator error, believe it or not. Believe it. I know, did it once.

 

I agree even though the particular caliper with the broken piston in question is is only a few months old and has never been touched since new hence the 🤯 emoji, lol.

But yes one way or another I'm accepted it's something I did wrong.

Thanks for the feedback @elder_mtber, I'll take a little comfort that I'm not the only one this has happened to, it's easily done and it ain't as rare as I thought.😎👍

 

can you brake the pistons from pulling hard your lever? i mean when you are in a panic mode and want to stop and you pull the lever real hard. can this shutter the pistons?

 

I really don't think so. It normally takes some sort of uneven pressure. Like pushing a piston back in with a flat head screw driver.

 

TRP uses steel pistons. And will sell you any spare part you need for a re build.

They just don't have the power of my beloved Zee/Saints.

 

TRP uses steel pistons. And will sell you any spare part you need for a re build.

They just don't have the power of my beloved Zee/Saints.

Agreed. Stupid that Shimano don't do spares. Lucky I had two old Shimano calipers lying around.

Since the shattered piston problem I've upgraded to SLX 4 pot calipers, no spares (for now) but just love the extra stopping power. Can't see myself ever going back to 2 pots again.

 

A bit of clarification;
The MT420 calipers have resin pistons. These are the cheapest 4 pots that Shimano make. They are still a good caliper, better that most Shimano 2 pots ?

The MT520 have ceramic pistons like the rest of the Shimano 4 pot range.
I believe they were produced for ebikes. They appear very similar to Deore 4 pots but with plain graphics.

Standard finless pads for the MT420/MT520 are the D02S (sintered) or D03S (resin).

You can also use the H03C finned, sintered pads or H03A finned, resin pads in these two calipers without modification. These finned pads were orignally for Saint/Zee calipers.

When purchased in a set the MT420 come with M4100 levers.
These are non servowave with an I-SPEC EV clamp.
The MT520 come with MT501 levers which are servowave with an I-SPEC II clamp.

The XT M8100 and SLX M7100 levers also work fine with both these calipers.

 

There's a good reason ceramics are prevalent.

I've never had any problems with any ceramic pistons/pucks. There have been a few.

 

Looks fine to me.

MT520 caliper
H03C finned sintered pads
'Risk' threaded pad retaining pin
203mm SLX RT64 rotor

I am also using XT M8100 levers

 

Looks fine to me.
View attachment 1982110

MT520
H03C finned sintered pads
Risk threaded pad retaining pin
203mm SLX RT64 rotor

I am also using XT M8100 levers

Yeah, nearly changed my mind, up close it looks....okay. 😎

I've fitted new SLX 4 pots onto old M7000 levers (i-spec II shifter). Running non finned sintered pads, 203/180 standard RT66 rotors, don't really need Icetech cooling for the type of riding and terrain I do.

 

I can see how fined pads would have a small effect on cooling.

I would love somebody to explain to me how 'Icetech' rotors do anything at all for cooling.
Cooling is about surface area and mass.
The only thing that the Icetech rotors appear to have is lighter weight.
This is pretty much the opposite of what you want for good cooling.

I am deliberately running RT64 (CL) rotors and my new wheelset will have RT66 (6 bolt) rotors.
As well as being the cheapest, these are the heaviest rotors that Shimano make that are rated for sintered pads.

 

Aluminum is a better conductor of heat than steel, the aluminum center of icetech rotors should draw heat out of the steel braking surface and dissipate it faster into the air due to the increased surface area of the finned rotor.

Heavier all steel rotors have more thermal capacity, but cool slower. It takes more energy to heat heavier rotors up, but but they also take longer to cool. They also have less surface area to disipate heat.

Basically an icetech rotor should dissipate heat faster and therefore cool faster. A heavier steel rotor should take longer to heat up, but will cool slower.

At least that's the theory.