This post give step by step instructions for eliminating disc brake squealing during braking. A separate post explains how to eliminate disc brake rub – during riding, with brakes released. If rubbing problem is present, do read that post first. Why? Following instructions given there, ensures that brakes are functioning properly and the calipers are aligned with the disc. That could eliminate squealing as well. If it doesn’t help, or there is no brake rubbing, read on.
1. Organic vs sintered brake pads
Short digression (click to skip it)
Main division of brake pad types is “organic” and “sintered”.
Organic brake pads (also called “resin”, or “semi-metallic”) are made of softer materials (kevlar, carbon, rubber with a minimum of softer metal particles).
Sintered brake pads (also referred to as “metal”, or “metallic”) are made of metallic particles (glued together using high pressure and temperature).
Differences of organic compared to sintered brake pads:
- They are softer, so they wear discs less.
- Generally less noisy when braking.
- A bit better braking when cold (“they bite right away”).
- They overheat more quickly and brake worse when hot.
- Worse performance in wet and muddy conditions.
End of digression
Why is this important? Some brake discs are designed for organic brake pads and if used with sintered pads they will make unpleasant noise. The only solution in this case is swapping either pads, or discs – so they are “matched”.
Not all the models of all the disc (and brake pad) manufacturers are so nicely labelled. In that case, look up manufacturer’s instructions/manuals (for both disc and pads, to see if they are “matched”). If there’s no manual available, last resort would be getting a two new pairs of pads: organic and sintered, mounting them (make sure the disc is cleaned, as will be explained in chapter 2) and seeing if one of them works fine.
2. Cleaning and degreasing
Dirty and greasy pads and discs are known to squeal when braking. How to clean them?
You will need:
- A cloth for which you are certain it isn’t dirty, nor greasy/oiled.
- Disc brake cleaner (available in auto shops), or alcohol with over 90% concentration (available in supermarkets). Both are FLAMMABLE, work in a well ventilated area, away from sources of flame, or heat.
- Sandpaper with grit around 80.
It is basically the same whether you use alcohol, or disc brake leaner. I’d say disc brake cleaner does the job a bit quicker (perhaps better), but can damage plastic, rubber, or paint (depending on cleaner model) so be careful. In the remainder of the text I’ll be using the term “alcohol” – it is shorter (you can use whatever you like).
- Remove brake pads. Clean brake calipers with a cloth, to remove any dirt, or brake fluid.
- Clean the pads using a (clean) cloth and alcohol.
- Place sandpaper on a flat surface (or a sandpaper holder) and rub the pads flat over it – to remove a thin layer of brake pad surface (don’t sand them down until they are worn, just remove the outer layer).
- Clean the pads again using cloth and alcohol.
- Clean brake discs using a cloth and alcohol. Clean them thoroughly. Dirty disc can contaminate the pads (and vice versa).
If pads have been contaminated with an amount of grease/oil that is not extremely small, they will suck it in (brake pad material is porous). In that case, no amount of sanding and cleaning will help. Some suggest to “burn” such pads in an oven, or on a stove. High temperature could burn the grease, but could also cause the pads to start to slowly lift off the metal that holds them in place (not always visibly). I wouldn’t risk this with brakes – get new pads… or don’t – it’s your bike, money and life.
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