Those Noisy Brakes

I love disc brakes. Love ’em! They have great stopping power in all conditions. They require less lever pressure than rim brakes — not that I’m weak!!!! They’re great, but they come with some baggage. Weight is one. Noise is another. “Why do my brakes make noise?” “What can I do about my noisy brakes?”

If your brakes — any brakes: mechanical, hydraulic, disc, rim — make noise, it means that something is vibrating at a frequency audible to humans. As bike mechanics, we work to figure out what’s vibrating and how to make it stop. With rim brakes, this generally turns into a project in which we subtly modify the way the brake shoes engage the rim when the lever is pulled.

Disc brakes noise generally has something to do with contamination in the system. Contamination can take many forms. I have owned and worked on bikes with brakes that are totally quiet on dry days but super noisy when the humidity creeps up. I have owned and worked on bikes with brake systems that are very susceptible to chemicals, oily chemicals in particular. Sometimes you can work the contaminants out of the system. Hard braking can help. We often try sanding the surface of the pads and cleaning the rotors with isopropyl alcohol. I’m gonna hit you with the truth ray here: these efforts are effective less than half the time. Why? Because the contaminants are baked into the rotor.

Ever cooked with a cast iron skillet? Those things are magic when they’re seasoned correctly and treated right. They can be super frustrating and hard to understand when they’re in poor condition. Your rotors are a cast iron skillet. Your pads are whatever goes into the skillet. If you ruin the skillet, new pads won’t help; they’ll just be ruined by the skillet (like your eggs). This analogy isn’t perfect, but it’s close. Heat is involved. Metal is involved. Porosity is a factor in both systems. Lots of things can be thrown into a skillet. Lots of stuff can come into contact with your braking system.

Vanishingly few (I’d like to say zero, but that seems boastful and impossible to prove) bikes leave our shop with squeaky brakes, so something outside of our shop probably contaminated them. Roads are gross. There’s all sort of bad junk on those things. Transporting your bike on a rack might contribute to contamination. Riding on the roads might do it. Transporting or riding your bike in wet weather — particularly right when it starts raining, before the roads are washed “clean” — up the odds quite a bit. I parked my bike next to an air compressor for several months before I figured out it was puking oil on my brakes. Nice!

If your disc brakes make noise, I would first make sure rotors and calipers are well-secured. The noise is vibration, so it makes sense to ensure that things aren’t vibrating more easily than they should. Rarely do we find loose things, but it’s a good, straightforward first check. Once that’s done, I would try to burn off any contaminants by making progressively harder stops, like maybe 20 of them. If that doesn’t work, you can sand the surface of the pads¹ and clean the rotors thoroughly in isopropyl alcohol, then make 20 progressively harder stops. If that doesn’t work, you can try new pads, but I think this is a gamble and suggest that you go for the full pads/rotors replacement. I am speaking to you as a friend who has cooked a lot of pads over the years. I am also, honestly, speaking as your friend who doesn’t want you to come back in the shop and say, “I put in new pads, but my brakes still squeal.” I want your business, but I don’t want you to spend more than you must.

It’s not impossible that you read all this and think, “My word! Why even get disc brakes?” To some extent, disc brakes are a sign of the times and are unavoidable. There are performance advantages, and noise is sometimes the cost.

1. “Sanding the rotors” might sound pretty vague. It is! You just need to remove a small amount of material. I’ve used everything from 400 grit sandpaper to gritty plumbers cloth. Sometimes I dry sand ’em. Sometimes I douse everything in alcohol and sand ’em. We have experimented with sanding the pads, dousing them in alcohol and lighting them ON FIRE (cue Jimi Hendrix) in an effort to burn off the contaminants. This is a lovely ritual to see and perform, but it’s not one with a proven record of success. Alas. ↩︎