Summer bike out of the shed after 4 months hibernating. Shim Ult Di2 12s groupset. Brakes were cleaned before hibernation and were ok before the clean. Cleaned them when out of the shed. Went for a test ride and bad noise when stopping. Cleaned / tested 3 more times. Cleaning for me means light sand paper then rubbing alochol on a dry clean rag (pads and rotors). Have used the bike a few times with a mini bed in down a hill. Very slight improvement so it’s only when stopping, not slowing down a bit. But still bad.
Pads and rotors not yet ready to replace. No signs of fluid leak. Everything looks ok. Also cleaned inside the caliper with cotton buds.
Any more ideas? Thanks for tips and anyone who helped on discord.
Simon
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You’ve done the main things already. You may have contaminated pads which doesn’t always show visually. Take the pads out and burn them off to get rid of any oil that may have seeped in during winter storage. Two methods: my preferred it to use a butane blow torch. This will get the pad mega hot so don’t overdo it. The other method is to put the pad in a shallow dish with a small amount of rubbing alcohol (keep the bottle capped some distance away for safety) and light it up. Quite spectacular and can be effective. Once that’s done and the pads have cooled, sand them lightly and if that was the problem it will be solved. If not, and you are certain there is no leaking (not even a tiny bit around the piston seals) then test with a new pad and then a new rotor to isolate the issue further. Good luck!
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Thanks. I’ll see if the neighbours have a blow torch or try the bowl burn. Otherwise try new pads.
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Torching a critical safety component is ill advised. Every brake manufacturer will tell you this.
Instead of using sand paper that burnishes the material back into your brake pads consider using an 80-100 grit sanding screen.
Spray the pads with soapy water, rub the pad material together, rinse and then use the sanding screen. Make sure the screen is on a hard and even surface, not a rubber work mat or bumpy work surface.
Use a 100-120 grit sanding sponge with soapy water on the rotor.
Rinse pads and rotors with rubbing alcohol.
Reattempt your bed-in carefully.
It is also a good idea to ensure the piston seals aren’t weeping. Shimano calipers are wont to do this when hanging for long periods of time.
If not weeping and still squealing it’s time for new pads and rotor.
Good luck!
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I also strongly advise against sanding the rotors for similar reasons plus you are unlikely to evenly resurface them and may make noise worse via vibration. Even turning modern automotive rotors properly on a lathe rarely solves problems for long.
If cleaning with acetone and applying some heat to burn off any remaining organic contaminants doesn’t clean a rotor sufficiently it’s just time for replacement.
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Thanks. I do use “extra fine finishing paper” so hopefully not too aggressive. I didn’t see any marks on the back of the pads to indicate a fluid leak, but not sure how pads or rotors would get contaminated with a bike stored under a tarp and with wheel covers over the wheels (including brakes). Bike is stored horizontally on its wheels. Also weird to me that it’s both brakes, so not just a random contaminant when i put the bike away or took it out.
I find that just general “dust” settles on things in storage – my area seems especially dusty – plus a little bit of oxidation happens while in storage. If I don’t get to ride my bikes for even a few weeks over I’ll find that the first good pull of the brakes produces a honk that then, usually, gets burned off.
With how easily automotive disc rotors seem to rust I’m always surprised bicycle rotors don’t but maybe they’re made of different steels.
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Well known issue with Shimano brakes, the pistons (especially the ceramic ones) slowly leak oil. Next time before hibernation, I recommend getting the pads out. In my experience, you have three options:
- Use a torch to burn the oil
- Go for a long, steep descent that gets your brakes really hot
- Buy new pads and clean the rotor before installing them
Cleaning contaminated brake pads with any sort of cleaner never worked in my experience, same goes for sanding them.
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Cleaned them, held each one over a gas stove for a few seconds, then cleaned again once cool. Worked a treat. My logic was that they couldn’t be worse and i have spare pads in the box, so why not? Went out and did a mini bed in procedure round my block (about a dozen slow-downs per brake). They worked great and did not squeal at all, not even a little bit. This winter i’ll take out the pads to be safe.
Thank you for everyone who helped me - i’m a happy chappie 
Simon
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I have a similar problem, but my brakes start squeaking on the next ride most of the time, even if it’s on the next day.
Shimano 105 with the finned pads. Horrible noise when clamping down, even at slow speeds. Is usually fine after a longer descent with interval braking, then the noise is back the next day.
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Likely the full contamination is not getting burned off in use, just the bit at the surface, so it seeps back through overnight, or you have a more severe seapage from the calipers.
Try removing the pads and blasting with a heat gun for a minute or two (until any smoke stops coming from the pads), and then see how things are.
If you have to blast them often, replace the calipers, and if you do this, try to get some of the newer ones that don’t have the problematic ceramic pistons.
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The burning method is very commonly recommended (google or Youtube it). The soap and water method isn’t effective because the oil is deeper in the pads. You are right, SRAM (for example) doesn’t recommend burning off - instead they recommend putting them in landfill and buying a new pair. Nothing is without risk, but I’m happy to back my own experience over 20+ years of disc brakes and many many thousands of other people’s experience.
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That’s brilliant, Simon. Glad to be of assistance 
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Hi Simon,
I have had the same issue so I’m happy to see this thread. I’m also glad you had a good result!
I have one question: How did you clean your pads?
Thanks!
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Light sanding with extra fine sandpaper, then spray with rubbing alcohol and wipe dry with a clean rag - this is my regular method of cleaning @Peter_Whitelaw
Im just happy I’m not the only one with this issue. I was convinced it was a leaky piston for a while. To the point where I put paper in between the pads and pistons and stored the bike for a week with the brake lever lightly cinhced, but nope, not a drop of oil seepage. I think it’s just some reaction with Shimano organic pads and environmental moisture.
Now if Im riding that bike for the first time in a while I just preemptively clean the pads with a spritz of alcohol and a light sanding and that (mostly) sorts it out. Im taking a cue from another commenter here and just pulling the pads entirely before next rainy season, maybe I’ll go really crazy and vacuum seal them with a dessicant.
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I’m going to remove the wheels, then remove pads and put a small plastic bag in the caliper before putting the wheels on. That way the caliper should be protected if there is any leak. I’ll still clean the caliper and rotor when out for the summer.
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Good info in this thread, and I have often used heat to remove contamination with success.
The screen vs sandpaper rec is a good one too, and the drywall sanding sheets are good for this.
The one point I’d add is that when using solvents it is important to recognize that the solvent penetrates into the pad material (especially organics) and needs time to dry before testing. This can be overnight, or by using heat.
If the pad is too “wet” when you go to use, it will glaze over during bedding or use, and become its own issue, often mimicking the original issue.
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Thanks @Justin_Walsh - I did wonder about this. When I gave the pads a clean after the burning I left out in the direct sun for a couple of hours just in case. And was a part of a successful process!
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I had this issue repeatedly happen to me on Ultegra R8000. Riding regularly in the summer it was fine but if you took enough time off the fluid would slowly flood the pads and ruin them. I ended up taking pads out over the winter or replacing them in the spring, but I never found a permanent fix before buying a new bike with Ultegra R8100 where they seem to be fine so far.