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#22 ·
Jayem said:
Shimano brakes are known to weep at the pistons, especially if they sit for an extended period of time. That gets mineral oil all over the pads.
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Any hydraulic caliper with damaged seals will leak. Why would Shimano calipers by any more or less susceptible to this than any other brand?
 
#23 ·
jeffbinco said:
Any hydraulic caliper with damaged seals will leak. Why would Shimano calipers by any more or less susceptible to this than any other brand?
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Because they weep even when they are not damaged.
 
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#24 ·
Jayem said:
Shimano brakes are known to weep at the pistons, especially if they sit for an extended period of time. That gets mineral oil all over the pads.
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Jayem said:
Because they weep even when they are not damaged.
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I must be doing something wrong, because I never had these problems.
 
#25 ·
SilentMTB said:
I must be doing something wrong, because I never had these problems.
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What can I say? It's a known problem. Doesn't mean every single person will suffer from it, but it's a real problem and I've verified it with shimano themselves. Their response was "yeah, we recommend removing the brake pads if you are going to let them sit for any period of time".
 
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#27 ·
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#28 ·
I have experienced these pad symptoms and never been able to validate any seepage. Several of us decided to take the theory to test by removing pads and incorporating a Dye Penetrant (NDT) and using only the developer to determine if any brake fluid is present at pistons. We performed test on four calipers with no positive indications of fluid presence. Note that all four of these brakes (calipers/pads) experienced the same phenomena repeatedly described in many threads. YMMV
 
#29 · (Edited)
I feel like a lot of these piston leaks could have been avoided by doing things right.

When you change the brake pads, you usually have to push the pistons in to fit the new thicker pads.
If you do it without opening the brake lever bleeding screw, you always run the risk of breaking either the piston seals or the master cylinder.

Why this? Because then there is a risk of over pressuring.
 
#30 ·
Cleared2land said:
I have experienced these pad symptoms and never been able to validate any seepage. Several of us decided to take the theory to test by removing pads and incorporating a Dye Penetrant (NDT) and using only the developer to determine if any brake fluid is present at pistons. We performed test on four calipers with no positive indications of fluid presence. Note that all four of these brakes (calipers/pads) experienced the same phenomena repeatedly described in many threads. YMMV
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well done.
I've had shimano OEM metallic pads seemingly lose power, after not being used for a longish period.
I never saw leaks or fluid stains on the pads or pistons. I've long wondered if the pad compound oxidizes or otherwise came into contact with something ambient causing the pad to go bad. Heating and sanding the pad solved the problem each time.

I've never experienced this problem with MTX ceramic pads.
 
Discussion starter · #31 ·
jeffbinco said:
I am confused how you were using RT56 rotors with metal pads. They are not compatible. Those are resin only rotors. It seems you might have been getting "extra" bite by literally destroying your rotors.

The RT86 rotors are metal pad compatible. But metal takes more time to bed in because it is so much harder.
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Wow! I never knew that. The rotors and pads combo mentioned above came with my then-new bike. I just looked at my old wheelset and the RT56 rotors and yes they're worn a little but not a crazy amount. Especially after 1.5 years of riding year-round. I'll reach out to Pivot and ask about this, although I am guessing they'll just tell me those are the standard pads that come with that brake set
 
Discussion starter · #32 ·
TylerVernon said:
Alcohol is for cleaning off sealant. If you want to clean off oils, use acetone or brake parts cleaner. I've never had to sand a contaminated rotor. Swap pads and rub down rotor with acetone. One advantage of Shimano is you can buy a stack of pads for a reasonable price so this process isn't a time waster.
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Thanks. I was always curious about this. I have a big can of alcohol that I've been using, but I will gladly get some brake cleaner or acetone. That may help solve this mystery along with the other good recommendations.
 
Discussion starter · #33 ·
Bikeworks said:
This was my first thought, especially when the OP said they pushed the pistons back in (which you're supposed to do obviously). I cracked a piston pushing it back while using the Park Tool piston tool (it's metal). From then on, I only used plastic tire levers. OP should pull the pads and inspect the backsides to see if there is any trace of fluid (even a ring stain). That's a sure sign you have a leak, typically.
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Thanks! Yes, I use a plastic tire lever as well and push the pistons back only slightly, enough for the new rotors to fit in the calipers with the new pads.
 
#34 ·
eastman said:
Wow! I never knew that. The rotors and pads combo mentioned above came with my then-new bike. I just looked at my old wheelset and the RT56 rotors and yes they're worn a little but not a crazy amount. Especially after 1.5 years of riding year-round. I'll reach out to Pivot and ask about this, although I am guessing they'll just tell me those are the standard pads that come with that brake set
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https://productinfo.shimano.com/en/compatibility/C-461 (everything you never wanted to know about Shimano rotors)
 
#35 ·
The Squeaky Wheel said:
well done.
I've had shimano OEM metallic pads seemingly lose power, after not being used for a longish period.
I never saw leaks or fluid stains on the pads or pistons. I've long wondered if the pad compound oxidizes or otherwise came into contact with something ambient causing the pad to go bad. Heating and sanding the pad solved the problem each time.

I've never experienced this problem with MTX ceramic pads.
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The only reason heat would work is its vaporizing the oil, like it does for me. Im not sure why people fight on this, but like I said, Ive confirmed it directly from Shimano. The more I ride, the less its an issue, but if not, its worse. I gave up and went to Magura, that dont have the issue so far. There were other issues too, but the worst was having to bake the pads and clean the rotors whenever I wanted to start using my XC bike again. It’s well known. I think its the ceramic piston models and possibly certain ones within those, but its well documented at this point.
 
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#37 · (Edited)
Just the data:
  1. BR-M7120 + D02S + SM-RT68 203mm: a stock setup that worked great aside from the fact that I would regularly warp it, but can also induce pad fade in the course of high-energy-dump tests. Therefore it sits on the rear wheels of my eMTBs.
  2. BR-M7120 + N04C-MF + RT-M800 203mm: could never get to work right despite lots of cleaning, rotor/pad sanding, baking, etc. It seems like I can never get these to the necessary operating temperature.
  3. BR-M7120 + MTX GL131 + RT-M800 203mm: worked great on regular days, but on colder days (this is California Coastal "cold", not inland cold), it would take a couple moments of application to warm up to stop the mild squeal and produce the right bite... but it would cool off (and exit the squeal-free + right-bite envelope) almost immediately. Had it on the front wheels of my eMTBs until I got tired of the squeal.
  4. BR-M7120 + MTX GL131 + SM-RT68 203mm: produces marginally better bite and warpage resistance than setup #1, and can't get to pad fade. This is what currently sits on the front wheels of my eMTBs.
  5. Bonus (gravel)? RX820 + K05S-RX + RT-CL800 180mm & 160mm: works fine from day one, but have not had the opportunity to put through high-energy-dump tests.
In other words, I gave up on getting N04C-MFs to work on Ice-Techs. I can otherwise get Ice-Techs to work right, kinda. I'm going to try the BR-M7120 + D02S + RT-M800 203mm combination soon.

I have had my share of problems with Shimano brakes, but none of this "piston weeping" business was observed by me, esp. with the SO's eMTB (which I have claimed in the above as "mine" since I speak for her on this forum) that gets to sit for very long periods without getting ridden.
 
#38 · (Edited)
Jayem said:
Yes, it actually happens.
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I believe you, I’ve had it with M8100 and M6100. Bike sits unused for a few weeks and there’s no power. Not only ceramic piston models, plus both resin and sintered pads. Since switching Codes problems has gone.

The Squeaky Wheel said:
well done.
I've had shimano OEM metallic pads seemingly lose power, after not being used for a longish period.
I never saw leaks or fluid stains on the pads or pistons. I've long wondered if the pad compound oxidizes or otherwise came into contact with something ambient causing the pad to go bad. Heating and sanding the pad solved the problem each time.

I've never experienced this problem with MTX ceramic pads.
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As above M8100 and M6100 both have done it for me. OEM metal and resin pads, same symptoms.

I thought it was environmental contamination with the bikes being in the house. Aerosols, steam/oil from cooking in the air etc. Covered rotors and calipers with plastic bags. Issue was still happening. Problem has gone away with Codes.


Cleared2land said:
I have experienced these pad symptoms and never been able to validate any seepage. Several of us decided to take the theory to test by removing pads and incorporating a Dye Penetrant (NDT) and using only the developer to determine if any brake fluid is present at pistons. We performed test on four calipers with no positive indications of fluid presence. Note that all four of these brakes (calipers/pads) experienced the same phenomena repeatedly described in many threads. YMMV
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I thought you’ve never experienced this?

j.bro said:
…. until they start weeping fluid out the piston seals. Then you buy a new set because they’re disposable.

Don’t ride them for a month and they’ve got no power.
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Cleared2land said:
Many years and miles on Shimano's and I have never experienced this.
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#39 ·
Macharza said:
I feel like a lot of these piston leaks could have been avoided by doing things right.

When you change the brake pads, you usually have to push the pistons in to fit the new thicker pads.
If you do it without opening the brake lever bleeding screw, you always run the risk of breaking either the piston seals or the master cylinder.

Why this? Because then there is a risk of over pressuring.
Click to expand...
This is the source of many problems that people report, especially caliper and lever leaks. Was not an issue with old shimanos, people assume they can keep pushing pistons like in the past.

From my experience shimano caliper pistons do not leak. When there is oil on them it is a results of the above, or cracking pistons, both are user errors.
 
#40 ·
CrozCountry said:
This is the source of many problems that people report, especially caliper and lever leaks. Was not an issue with old shimanos, people assume they can keep pushing pistons like in the past.
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In the past ~2 years I've had 3 Shimano levers start leaking at the master cylinder.
The last one started leaking after about 2-3 months of use. The whole brake set was new, I haven't even touched the pistons yet.
 
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