Disc Brakes and Pads that *DON'T* squeal?

[alexfthenakis]

Based on everything you’ve tried and the fact you’ve replaced calipers more than once I’d echo @Gnome and suggest checking whether the mounts need to be faced. I can imagine if the facing is bad enough it could even make leaky seals more likely (if they’re forcing the piston to sit wonky in the caliper) but I suspect it would have to be unusably bad before that would happen.

Also worth taking a page from @batwood14’s anecdote and doing a really thorough investigation to rule out some really weird unexpected contamination source like a third party with cleaning spray when you’re not even home.

And I’ll echo a few different warnings about being too obsessive/proactive in trying to address issues too, but not because of additional contamination risk as suggested by others: The lesson that took me longest to learn is that all of the ‘fixes’ really only get you about 90% of the way there. The only way I’ve ever found to truly finish the job is just to ride hard for a couple hours on a really dry day, and that alone is also enough to deal with quite a lot.

Here’s how I phrased it in a different thread (shamelessly including the endorsement I got from another user )

@bmcd

@alexfthenakis

Over the years I’ve had about half a dozen shimano hydro road and gravel bikes sharing about a dozen wheelsets between them. I think I’ve dealt with most issues now and have come to the following conclusions:

• Most glazing, bedding in, and even relatively significant contamination issues can be dealt with pretty easily with about an hour or two of hard riding in some moderate hills/corners on a dry day.
• It takes relatively little moisture in the air or on the road to ensure that almost any amount of sanding, cleaning, bedding in, replacing, lighting on fire, etc. is never going to fully solve the problem.
• Uneven pressure from a sticky piston is a hidden component of a lot of issues, and there’s a 9/10 chance that I’ll end up realigning the caliper before I remember to check whether it’s really caliper alignment or just a sticky piston.
• Shimano piston seals have a particularly bad knack for getting damaged by retracting dirty pistons.
• A leaky piston seal will almost never be bad enough for me to notice any oil leaking except by looking at the backing plates of the brake pads.
• Rubbing alcohol is plenty for dealing with 99% of all contamination except when the source of the contamination hasn’t been addressed properly (such as in the case of leaky seals).
• Shimano will warranty nearly all issues with piston seals with no questions asked as long as you’re still in warranty - otherwise it’s either caliper replacement or buy 3rd party seal kits.

So my tips to others are always:

1. Check the brake pad backing plates for signs of leaky seals
2. Clean, lubricate, and excercise pistons (only realign calipers if necessary AFTER this step)
3. Clean rotors and pistons (and sand/replace pads if necessary)
4. Bed in on a dry day. Standard procedure is fine to get started but you’ve really got to go ride hard to finish the job.
5. Sand and retry if needed.
6. Replace pads, clean rotors, and retry if needed

This is the way.

And another version of much the same info that I wrote out for someone in my club’s facebook group:

My top tips (n=1, may not apply to all, etc.):

1. Cleaning, de-glazing, blowtorching, sanding, bedding in, etc. can all be helpful but none of them will get you 100% of the way there. Only way to really finish the job is about an hour of hard riding on some hills on a really dry day, and that alone can take care of an awful lot of issues without even getting into the other stuff!

2. A dry day means REALLY dry. Puddles, big runoff patches, slightly misty air, etc. are all enough moisture to keep things from settling. Clearly Shimano brakes weren’t built with Scotland in mind

3. Sticky pistons are a hidden component of a lot of issues but I forget to check this every. single. time. To get one moving again you need to remove brake pads, squeeze pistons out a decent amount (possibly whilst holding the non-stuck one in so only the sticky one moves), clean with spray cleaner, then clean the circumfrence of the piston with a cotton bud dipped in mineral oil, then push them back in. Might need to squeeze out and retract the sticky one a few times to get it moving smoothly again. Once they’re both moving evenly push them both all the way back in and clean with spray cleaner to get rid of remaining surface oil before reinstalling the pads.
   We should really be doing this (or at least checking piston movement) before even considering realigning calipers.

4. Separating wheels from bike for any serious washing can be a big help. Much easier to cover the calipers when dealing with anything oily/greasy that way, and if there’s any concern about what might have got onto the rotors you can give them a light wipe with some alcohol before reinstalling wheels. Requires a mini-bed-in at the start of the next ride which can be scary if you forget about it until you come up to your first red light of the day, but they’re back to normal after 2-3 stops.

5. Scotland can’t make road discs hot enough for sintered pads to be worth it and we’re actually better off with the lower operating temps of the organic ones. MTB might be a different story given how much mud we have, but definitely no need on road.

6. The only bike that has any hope of being quiet in the wet is one that that regularly gets ridden hard in very dry conditions. Some noise when wet (especially on initial bite) should be considered normal. If they go quiet once they heat up enough to dry off then they’re working as intended and it’s not worth the time/energy/money to hope for better than that.