++BLUP++ I don't manage to bed my new pads properly. They come out glazed and squeal terribly at very low speed.
I have a shimano 105 setup (R7070, RT70-S and K05S-RX pads). Roughly 10k on the rotors.
Just for info: bled the system, cleaned the rotors (brake cleaner, lint free cloth, isopropanol). Installed the same shimano pads-new out of the box.
Tried bedding with one method I found: ride hard, brake hard–didn't work. They hardly braked and came out glazed.
I sanded them down with 200, put brake cleaner on and…
…Tried second method: ride hard, brake slowly, repeat 20x–did not work either. Brakes don't "catch", they generate friction and eventually start shrieking like hell.
Taking the pads off, they are all glazed again.
That's rear. Front is better but also has a "glazy shine" and these stripes all over yet has a more catchy feel.
Is it the rotors then? There is a brownish shine on them. Or simply my ignorance?
Any advice is appreciated.
by Muixca
19 Comments
Your pads are contaminated with something oily. It doesnt matter how many times you sand or clean them, they will not bite, and they’ll make noise. Easiest path forward is replacing the pads and cleaning the caliper and rotor with IPA. I dont find that sanding the rotor is necessary in most situations, and it just makes the bed in process take forever. In a pinch, I have had an almost 100% success rate with blow torching the pads until they smoke and the contaminants burn off, followed up with a quick sand, acetone, and wipe with an unused towel.
Honestly, just buy a new set of pads, they’re not that expensive. Yours are contaminated and resin pads will eventually soak that in and ruin your pads. See YouTuber bike mechanic Stu over at : Barn Cycle Repairs.
If you want to verify if you Pads are contaminated, sand them with an Emory cloth or high grit sandpaper.
The pads will turn a uniform brown color. Let the pads sit for 15 minutes. If they discolor to a dark brown/ blackish color, then that is brake fluid in the pad.
If they don’t change color, then your pads are fine.
I recommend using Squeal-Out on the rotor, as it is more effective than sanding rotor surfaces. Used properly, it will create a coarser surface for the brake pad to drip to.
Follow the bedding process described in the packaging if you use that product.
Otherwise, you have to find a different way to create a rough, grippy surface on your rotors.
Perhaps a coarse wire wheel/disc in a drill to rough up the surface.
It looks like your calipers is totally out of alignment. Show us the full setup.
I wanted to confirm you’re not braking to a full stop during the bedding process?
Do you have access to a treadmill?
My favorite method in your case (if you’re resistant to purchasing any replacement parts) would be to sand then burn the pads & rotors. I burn them with isopropyl alcohol.
Then slightly wet the pads and rub them together to generate a little lapping compound. Put the brake pads back into the calipers.
Then I use a treadmill to spin the wheel while slightly applying the brake, gradually applying more pressure. This builds up heat, and facilitates deposition of pad material evenly to the rotor resulting in a good quality bed in (with a uniform tribofilm coating on the rotor).
Repeat the process with the rear wheel.
This is a method I adapted from a professional downhill mechanic who did essentially the same thing, but used a hub driven by a drill to pre-bed in matched pads & rotors to swap on downhill bikes between runs.
Brake hard but not completely. You don’t want to lock the wheel, you want material from the pad to transfer evenly to the rotors. I’d restart and try again with new pads.
Honestly I just prefer to replace the pads and rotor. Cuts all the faff and just immediately fixes the problem plus it can be pretty cheap.
Are you sure the pads are genuine Shimano ones?
I had something similar happen to me. I tried sanding with alcohol as a lubricant , holding the pads over my stove burner etc….they just wouldn’t bed. Kept glazing over. I didn’t think they were contaminated either because I set up the bike and never got oil on them.
As a last ditch effort before buying new pads, I took a bastard file to the pads, and scored them fairly heavily, trying to add texture. That actually helped quite a lot. They brake probably 80 percent as well as my other hydro brakes on my other bikes. At least I’m getting some life out of them before I eventually end up with new pads
I was wondering why noone else mentioned that, he’s maybe using 75% of the braking ring on the rotor, and there’s definitely an area on the pads with no contact to the rotor.
Have you checked your caliber is not leaking? I kind of went through the whole process as you all described and do finally changed the caliber. Fixed everything. Another important things is to just use your brakes.
Kooma ceramic pads. No bedding in required as it bites from the first second.
Had similar issues. I changed out both rotors and all the pads. Noise gone, brakes work great.
Replace the rotors with Sram rounded rotors it will brake like a charm. Its the best thing i ever did.
Are your pads the same type as the ones you had on there? (Resin or metalic?)
The recommended shimano bedding in procedure is to pedal to a moderate speed the slow the bike down gradually and release the brake before the bike comes to a stop, do it 10 times for each brake and do one break at a time. I don’t think you want to get the breaks to hot when bedding them in.
The first thing you need to sort is that you’re using the wrong size brake adapters. Your pads aren’t fully contacting the disc.
Being very anal rentative about following a bed in procedure is largely a waste of time unless you urgently have an event or race the next day, and need top performing brakes immediately. Or if you’re riding steep DH just off the chair with new pads (don’t do that LOL).
Just go for a normal ride and plan to do some bedding in while you’re on it.
Buy new pads, lightly sand your rotors and hit ’em with a bit of isopropyl and then a very light heat e.g. plumbers torch both sides and they should be fine. Then install new pads and go for a normal ride (not the steepest double black on the mountain).