Ryan_M

I have/had 3 bikes with squealing rear disc brakes, though one seems to behaving itself so far. Makes sense the rears woud get contaminated first but this is a bit much. I've gone so far to sand down the rotors with nonmetalic abrasive pads, faced the pads to get to fresh material. Cleaned all surfaces with acetone, isoproyl, and plain water, in various orders with no success. My roadie (L03A pads) I spent a lot of time with redressing everything, reseating, even went up and down a few hills with the brakes on to cook off any nasties and it totally worked! was silent until the next time I rode the bike.... It's squealing again. The Shimano pads are not cheap. I've got some knock-offs en route to give a try, seems ridiculous that bike brake pads would cost more than pads for my car lol

So I'm curious if there's something I havent tried yet to get the brakes to not squeal.

Iride01 

Is the rotor rubbing one pad constantly and staying heated up? Absolutely no oil or cleaners getting on your rotors when you clean it after rides? Just a little over spray of some cleaner or preservative might let it squeal.

How much did you pay for your L03A pads? I haven't put pads on my cars for less than 80 bucks a set for a long while, recently over 100, just for the pads. My L03A's were about 30 bucks or a tad less IIRC.

easyupbug 

May not at all be your problem and I don't like the sound of "cook off the nasties" which is the opposite of what we want to do. Here is what we do that works well:

bikeme

Truckerco for aftermarket pads—great price, work awesome. Have used them on road and mtb. No fins though, doesn’t seem to be an issue. I like their semi-metallic version. They have sintered but the SMs wear less and stop better than full resin/organic without the faster rotor wear of full sintered. The latter is good you’re a heavier rider, in hills a lot or ride in wet conditions.

Ryan_M

Nope, no rubbing, alignment is spot on. Nah nothing getting on them aside from dust, I'm a fairweather rider too so not even rain. I'm also very diligent of not toching them and wear nitrile gloves if I'm going to be handling the brake parts directly to avoid any oily digit prints. LOL the coment about their cost was kind of a ranty exageration, but turns out accurate. The L03A cost $40ish here (Canadian pesos), add tax and shipping and it's ~$60 to get a set in my hands. I can get a standard set of rear ceramic pads for my car for about $100 but that includes 4 pads total, so yeah they are more expensive. I know there's supply issues but that pad material better contain groud up unicorn horns!

Yep that's the standard method. I guess I didn't explicitly say it but I've exhausted all the usual things to do, hence the thread. When I lapped the pads I only went so far as to expose new material, maybe I'll try taking a little more off, and possibly get some more aggressive solvents than acetone that I can get from work. I'll have to take the bike to an uninhabited area though before I get complaints from the neighbours. I've already started one fight:

A house on my street had the front door open while I was trying to bed the brakes in...
Wife yells - What the hell is that noise!!!
Husband yells - How the f*** should I know?!
<arguing intensifies>

I'm also wondering about the abrasive I used to try to remove any glazed on material from the rotors. I used a 3M burgundy pad, which AFAIK is an emery abrasive. I have 400 to 1500 SiC wet/dry paper, not sure if I have any AlOx that's fine enough. Thoughts on what's best to use?

Kai Winters

"Squeal Out"...Amazon...use it at the shop and it works fantastic...brake squeal is an awful sound

daverup 

If you have hydraulic disc brakes and the caliper piston seals start to leak, a tiny bit of the fluid will cause squeal once it reaches the pads.

easyupbug 

You have a tuff one, the paste suggestion for removing any glazing and cleaning the pads is a good one even if it does not work for any length of time as the problem would be narrowed down to be the pads.

Iride01 

How much pad do you have left. If you aren't down to .5 mm on the pads and 1.5 mm on the rotor then you might try sanding them. Though you need to be sure those are the limits for your Shimano brakes. That's what they are for my brakes and rotor.

And use a block under the sandpaper so you don't start making a uneven surface. Not a 3m pad or something soft that will gouge out the softer parts and leave low and high places.

Otherwise get all new. And don't go crazy trying to bed them in whether it's the old ones you sanded or all new pads and rotor. Just firm braking and not to a complete stop. I didn't bed mine in at all. I just did normal braking and 300 miles later they were very effective at braking and no noises except for briefly in wet conditions.

And be certain the rubber boot around the pucks are clean and no oil seeping out. A tiny drop of oil every few 100 miles might be your issue too. A q-tip or swab will let you get up in there.

Ryan_M

Success!!!
First credit where it's due...
FWIW the gear is nearly new, probably less than 1000km on it, but of course I sould use a block instead of an abrasive pad. I'm kind of embarrassed that I didn't but those are the lessons you remember!

So I wet sanded the rotors with 400 SiC until I had mostly pure stainless showing. I also lapped the pads with the same, hard to describe but you could feel the difference in resistance when I got through the glazed on crap. I cleaned it all with acetone then got out the torch! I know some of you are cringing but there's more than one instance out there of this helping purge the pads of any contamination. The idea is get hot but not cherry hot. I put the pads in the vise and put the flame to the back side. It smoked a little but I didn't know what to expect since it's resin and all. The second pad started on fire! I let it burn off and reappied heat which started it again on fire. I stopped after it stopped self igniting. Cleaned it all again and put it back together.

I went out for a quick boot to bed in the brakes and they feel maybe better than brand new, totally awesome and not a hint of any noise. braking power was also surprisingly strong. I have a leisurely 70km ride with the club tomorrow so we'll see how it goes.

Canker

Yeah I don't know why people poo poo the torch and it is exactly what I was going to suggest. I've done all the other standard decontamination methods but the only one that always works is getting out the propane torch and burning the contaminates off. They are brake pads and are made to withstand heat.

easyupbug 

People poo poo as it is a last resort for effectively removing contaminants, that we try to keep off.
.

Lars Halstrom

You’ll be further ahead by buying new pads and rotors or you’ll be chasing this on and on.

Ryan_M

Nope. The torch fixed it, for now at least. Probably 300km on it and it's still solid. A bit of time and a few pennies of propane is way better than ~$120 for a pair of new pads and a rotor.

I get its a last resort when you've tried everything else option, but it worked.