This post gives you 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 here 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).
Picture 1
Sintered brake pads (also referred to as “metal”, or “metallic”) are made of metallic particles (glued together using high pressure and temperature).
Picture 2
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”.
Picture 3
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).
Source: forums.mtbr.com, member WR304
Picture 5
Note:
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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The existing comments posted under this article (questions and answers) have been moved to this BikeGremlin forum thread:
https://www.bikegremlin.net/threads/eliminating-disc-brake-squealing-article-comments.153/
Hi I have the latest M6100 Deore brakes. they work great BUT when riding in very muddy conditions there is a horrible graunching sound when NOT braking. It sounds like tiny particles of grit in between the pad and disc. I have the same problem on my M615s on another bike. Has anyone else had this problem? What is the solution? The calipers are perfectly aligned and the pads do not rub when not braking. I have never had this problem with Sram brakes. Any ideas would be appreciated Tony
Hello,
First appologies – your comment got put in the “spam” section (no idea why, computers err too I suppose), so I had to correct that injustice “manually”.
As for your question – just to confirm: brakes don’t rub when riding on paved roads, but in muddy conditions, they start rubbing?
Discs are away from all the dirt, but aren’t immune. I suppose it is possible for some dirt to be sprayed on the discs and cause rubbing. Haven’t experienced that myself with disc brakes, but maybe that’s just down to not riding in muddy enough conditions. 🙂
Perhaps the fact there hadn’t been any rubbing with SRAM brakes was just a coincidence? Maybe it’s only environment/riding conditions related.
I’ll have to check with a friend who rides often in deep mud, to see which model his brakes are, and whether he’s experienced the same problem.
Hello, I have an issue where at nearly all speeds, my m6100 4pot deore brakes are completely silent, however at low/stopped speeds, there is a very loud squeal, and the brakes aren’t as effective as when the bike is moving (ie the bike will squeal and move if i’m sitting on it with the brake fully in whilst not moving). I would appreiate any advice, thanks.
ps i am running resin pads and 180mm smrt86 ice-tech rotors.
Hello Luca,
On bicycles with rear suspension (if your has that), rear brake can pivot around the wheel as the suspension travels up, and down.
That’s the first thing that comes to mind if the noise is made when stationary, or almost stationary.
But why do they squeal at low speeds, and not at high speeds?
Possible problems that pop to mind:
– Some dirt stuck between the pads and the disc can cause that.
Fix? Try cleaning the disc and the pads with 95+ % alcohol, and see if it’s eliminated.
– Very slight misalignment of the brake calipers (and, hence, pads) compared to the disc.
Fix? Check the alignment, by loosening the bolts, then re-aligning the calipers.
– One brake piston is a bit “lazy” – not moving back-and-forth as easily. So the disc gets slightly bent when braking. This could cause a similar effect to the brake caliper being slightly misaligned.
– Material combination, creating a resonating frequency only at low speeds.
Fix? Try sintered pads. They are harder, different material structure, so their resonating frequency will be different. It might start making noise at different speeds, but if the noise is gone at low speeds, I’d suspect the resonating frequency to have been the problem. Of course, some discs aren’t designed for harder pads (like sintered). And sintered pads do perform worse when cold.
On some motorcycles, I’ve fixed such problems by smearing some copper grease over the rods that brake pads slide back-and-forth over (copper grease is high-temp resistant, and won’t melt and contaminate the pads). Haven’t had bicycles that needed this before, but think it’s worth noting.
How to align a disc brake caliper
How to fix a stuck (“lazy”) disc brake piston
Let me know what it was when you manage to figure out the problem cause. 🙂
Relja
It’s me again!
My rear brakes were howling really loudly the other day and I changed the rotors and pads.
However, I noticed now that I get a howl for a very short period of time at the start, which then disappears for the rest of the ride. If I let the bike cool for about 3-5 minutes and start riding again, it howls once again for a short period of time.
I then realigned the disc brakes once again (note that it wasn’t rubbing in the first place before and it didn’t seem to bend the rotor when braking) and it seems that the howling has disappeared.
Any idea how a very slight misalignment could result in a howling noise? Just out of curiosity.
Hi Reuben,
I suppose that pad and rotor temperature plays a part – affecting the resonant frequency, as well as the alignment (through heat expansion).
In my opinion, it boils down to the fact that disc brakes need to rub in order to work properly. Car and motorcycle manufacturers managed to get them working properly only after they had realized that slight rubbing doesn’t hamper vehicle performance, nor overheat the brakes. Before that, when they were trying to make disc brakes work with zero-rubbing, the results were pretty bad (in terms of braking power and modulation).
With bicycles, since our “engines” are relatively low-powered, any rub is noticeable in terms of performance (speed) reduction. Also, since there’s no high-powered engine noise, or wind noise from going over 40 km/h most of the time, any rubbing sound gets rather irritating.
So bike manufacturers tried to re-invent the wheel by doing what top-class automobile engineers had concluded is not really possible – making disc brakes that don’t rub. To make the challenge even more difficult, with bicycle brakes, any extra weight is very, very difficult to sell.
The result is what we see now – brakes that often rub or squeal, so that every wheel change makes you think “will I need to re-align the brake calliper?”
But that’s quite good, compared to the difficulty of the challenge – making disc brakes that don’t rub. The problem lies within our current (capitalist) economic system – manufacturers need to make sales, and planned obsolescence is everpresent, resulting in most modern bikes being sold with disc brakes, even if the bikes are designed for riding on pavement, not in mud and snow. With the marketing departments trying hard to convince us that disc brakes are be-all-end-all when it comes to bicycle brakes – as if top braking performance in muddy conditions is more important than the lightness, simplicity and no-rubbing for grocery-shopping, or road riding bicycles.
Relja
Thanks! This was super helpful!
Hi Relja,I am fixing up another old retro racer,it has the older aero brake levers on it,the rubber hoods that cover these levers were all perished and my attemps at finding replacement hoods was not possible,its actually easier to buy whole new brake levers,but as these levers were still working good i cut an old mountain bike tube and made hoods from them,it works fine,cheers
Hi Mike,
That’s a cool hack – glad you could help the levers keep going. 🙂
But yes – it’s often easier to change whole assembly, than it is to find some wear and replaceable part that would be reasonable to make and sell for replacement.
Relja