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:
- Check the brake pad backing plates for signs of leaky seals
- Clean, lubricate, and excercise pistons (only realign calipers if necessary AFTER this step)
- Clean rotors and pistons (and sand/replace pads if necessary)
- 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.
- Sand and retry if needed.
- Replace pads, clean rotors, and retry if needed
I’ve never actually got as far as having to replace a rotor for any reason other than reaching minimum thickness.