My disc brake pads seem to have plenty of material left but they somehow got contaminated and squeaky. I tried sandpaper on the pads to freshen the surface, and cleaned the rotors which helped for a while. The rotors are still stained though. I can’t stop the squeal in the last ~20% of lever throw. I don’t need a bell when slowing down to alert nearby riders
Can I lightly sand and/or clean these rotors and use with fresh pads? I’m trying to figure out if there’s contamination on the rotors themselves that could ruin new pads.
Firstly squealing is not a sign of contamination, a reduction in braking force or a complete inability to stop is. My brakes always squeal when they are wet. its just what disc brakes do. A few hard stops when they are dry and the squealing goes away.
If you can stop safely with your current rotor and pads, I wouldn’t worry about the squeal.
If you’ve removed the pads from the calipers, and the wheels from the frame, even with thru- axles this can cause a tiny mis-alignment which can cause squeal. I always loosen my caliper bolts and retighten with the brakes on after re-installing the wheels.
Follow the directions and it will stop your squeal….however, it is not a permanent solution and you’ll need to reapply after awhile. But it definitely works.
Just make sure you follow the directions….if you just slap it on and start riding, you will significantly reduce your braking power.
The rotors have lots of dark streaks and the surface of the pads looked gunked up (is that the technical term? ) before I sanded them the first time. Braking force is fine but they squeal when bone dry with the last squeeze of the lever to come to a full stop. Alignment seems OK visually anyway.
I have had success sanding rotors to resurface, it helps get all of the bedded pad material off. I think this is important if you’re switching pad compounds or you’ve been dealing with contamination.
Some tips: Wear latex / rubber gloves to keep all oils / contamination off the rotors. Clean very thoroughly with acetone first, alcohol second to remove all residue possible. Brake Cleaner works too but I always follow up with Alcohol. Use clean new wet/dry sandpaper, I think I used 400 grit but possible more coarse (I’ve heard of steel wool too but haven’t tried it). Easier with the rotor off the bike and a small sanding block, I went in two directions trying to create a cross hatch pattern. But, have to admit I’ve just done it by hand on the bike too. When you’re done, clean with acetone and rubbing alcohol again. If there’s any question whether your pads have been contaminated by any sort of oil / lube - pitch them and use new, they cannot be salvaged if contaminated. Otherwise, you can sand down to create a fresh surface, blast them clean with brake cleaner and reinstall. Then, make sure to properly bed in your new pads.
With that all said, I use metallic pads and they can squeak and squeal even when perfect. Some pad compounds will do that depending on temperature, wet or dry, etc.
I’ve had this exact problem, and have personally had great luck cleaning my rotors thoroughly with rubbing alcohol and a clean fabric rag (don’t use paper towel, it’ll fall apart).
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.
I didn’t see any mention of pad material. In my experience, metallic pads are gonna squeal under some conditions (especially when wet) regardless of what you do. If the noise bothers you, switch to resin pads. They are much less prone to squealing (but wear out much faster and don’t quite have the bite you get from metallic). Personally, i prefer metallic but the noise doesn’t bother me. It’s really only obnoxious when riding in the rain.
Don’t mix up squealing that sounds like a honking goose (pad contamination) with metallic rough sound (proper). Soak rotors in ipa and sand pads or heat with propane torch.
) before I sanded them the first time. Braking force is fine but they squeal when bone dry with the last squeeze of the lever to come to a full stop. Alignment seems OK visually anyway.