InvertedMP 

My new bike has a horrendous squeal when getting on the brakes firmly. What can I check to get this quieted down?

spelger

new bike? don't know much about disk brakes but your seller should. hopefully they are local.

eflayer

1. the brake pads were not bedded in properly when installed. if done right then they don't make noise.
2. some crud got on rotors or pads or both and that dirt causes the brakes to make noise.
3. replace pads, clean rotors, and re-bed the brakes

easy one is to clean the rotors with non petroleum product, maybe alcohol. then try the brakes again.
harder one is to remove the pads and clean by sanding down a bit.
doing both of the above worked for me.
harder and more expensive is number 3.

illdrag0n

Just flush everything out with aerosol automotive disc brake cleaner and wipe your discs down with a clean rag. You've contaminated your pads with something

MoAlpha

To deal with potential contamination, clean your discs with clean cloth and a safe organic solvent, such as rubbing alcohol, and cook your pads in a gas flame for about 20 seconds. If they're still squealing after that, it's a mechanical issue.

InvertedMP 

So I just put this bike together from a flat bar bike. I did something to make them squeal and now I can't get rid of it. I did get mineral oil on them during the bleeding process but I wiped everything with alcohol, and sanded the pads. Still no luck

Greiselman

I'd guess you need to finish the bedding process.

https://cyclingtips.com/2018/03/road...brating-noise/

fooferdoggie 

I discovered this degreaser will blast thbrake material off the rotors so you can re bed them fresh. alcohol in a spray bottle works well too but this is good to clean the rotors from a poor bedding finish line speed degreaser.
https://www.amazon.com/Finish-Line-S...10935526&psc=1

badger1

If you contaminated the pads with mineral oil, and especially if they are so-called organic or resin pads, clean (really clean) the rotors, bin the pads and install new ones. Make sure you've got any traces of mineral oil (brake fluid) off the calipers.

Check the alignment, and bed the new pads in properly. Should solve the problem. Fussing around trying to save badly-contaminated disc brake pads isn't worth the trouble in my experience, though some seem to have better luck with that than I have.

noodle soup

+1

First rule of bleeding brakes - Always remove brake pads before bleeding. Use a brake block like this.

PoorInRichfield

My favorite brake pad cleaner is a propane torch. Take the pads out and cook their little brains-out (and obviously be careful because they'll be really hot). I've gotten my Shimano XTR and Ultegra rotors red hot and watched them smoke a little as the contaminants burned off. Attempting to clean the pads with sprays and chemicals often just pushes any oils further into the pad. I then use rubbing alcohol on the rotors and this combination has so far been able to quiet some severely annoying hydraulic brake setups.

InvertedMP 

Thanks guys, lesson learned the hard way for my first disc brake venture lol. I’ll grab new pads today. I might try and torch these, but also meh lol.