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Fixing squealing hydraulic brakes.

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Fixing squealing hydraulic brakes.

Old 02-22-24, 11:35 PM
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Fixing squealing hydraulic brakes.

There's quite a bit of advice on the web about how to fix squealing hydraulic brakes. I have put together the good advice I've seen, and my own observations and experiences.
Please add your own ( and, also, let the flaming begin)....If your hydraulic brake is squeaking or howling, I’ve found, through making many mistakes, that the following helps…

1. The awful sounds are usually caused by oil contamination of either the rotor or the brake pads, usually both (they contaminate each other). Note: the brake pad can absorb oils.
2. The brake caliper often has a buildup of crud on it (as does the surface of the pads, especially if the pads have cooling fins, which can trap lots of crud). When you remove brake pads, this can disturb the crud. Some of this often oily crud may drop onto the rotor or brake pads. Removing the wheel from the bike is best to prevent oily crud from hitting the rotor when removing the brake pads.
3. To clean the rotor (don’t touch the surface of the rotor with your hands while doing this… your natural oils can contaminate the rotor):
a) Removing the rotor from the wheel makes the following easier and probably more effective.
b) Wash the rotor with soap and water to remove water-soluble contaminants, then thoroughly rinse the rotor, then dry using a very clean cloth or paper towel.
c) Using steel wool and rubbing alcohol (or bicycle-specific disk brake cleaner) to remove oils from the rotor. Aggressively clean both sides of the rotor using the steel wool.
4. To deal with the brake pads:
a) Remove the wheel to prevent contamination of the rotor that could be caused by crud dropping from the caliper onto the rotor when you’re removing the pads.
b) Remove the brake pads.
c) Thoroughly clean the entire surface of the caliper, including the surface of the pistons, and the areas surrounding the caliper using rubbing alcohol or a bike-specific brake cleaner, applied to a clean cloth or paper towel. The brake dust and other dirt that gathers around the caliper can absorb oils that your bike picks up during your rides. Check for any buildup of crud around where the hydraulic brake hose enters the caliper… this indicates that you may have the tiniest hydraulic leak, which will probably cause contamination. If you have a leak at the caliper/hose connection, it’s doubtful that tightening the hose connection will help… for this connection, tighter doesn’t mean better. If you haven’t had experience with brake hoses, take the bike to a bike shop and tell them about the leak. They’ll separate the hose from the caliper, replace the hose insert and olive, and tighten the hose back onto the caliper to the correct torque.
d) If your pads are very lightly contaminated, try rubbing the surface of the pad against waterproof sandpaper, laid flat on a table. Do so in a figure-of-eight pattern. A few drops of rubbing alcohol or brake cleaner help. I’ve found that cleaning the pads is rarely effective, so I now just buy new pads, making sure that, before installing them, the wheel is off the bike, the caliper body and the rotor have been thoroughly cleaned, and that there isn’t a leak from the junction of brake hose and caliper.
Some suggest baking the pads in an oven, although I haven’t tried that yet.
One thing I learned the hard way is that the rotor and pads contaminate each other. Cleaning, or replacing, one means that one must clean, or replace, the other.
5. When bleeding the brakes, I find that I get oil, which can contaminate rotors and pads, everywhere. I now remove the wheel (remember to put a caliper spacer into the caliper when you do this; it’ll prevent the pistons from moving too far towards each other if you accidentally press the brake lever) and brake pads and put them in another room before starting the bleed process. After completing the bleed, clean the caliper and area around it using rubbing alcohol or a bike-specific brake cleaner, before replacing the wheel and brake pads.
6. After cleaning/replacing the rotors and pads, bed-in your brakes.
7. Caliper alignment may also be a problem, but that has not been a problem for me, therefore I won't add my two cents to advice already on the web.

My system is Shimano Ultegra 11-speed hydraulic Di2.

Last edited by kirbyx; 02-29-24 at 04:42 PM. Reason: Added the two last lines: might be useful to people who find this thread in the future.
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Old 02-23-24, 05:11 AM
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I'm not a disc expert, I have no bikes so equipped. But no mention above regarding any pad alignment issues, but I don't know if any adjustment is possible there. Squealing on rim brakes is often caused by pad misalignment. A squeal comes from vibration, so something is oscillating very fast, especially for a higher pitch. For example, the pad/caliper could be deflecting, then snapping back, a couple hundred times a second. So rigidity of everything, mating angles, etc, all matter. Note: Car disc brake pads often came with an anti-squeal kinda rubber cement, that if I recall, was applied between the pad and caliper piston.

Also, buildup of rust/metal particles on the pads from the discs, can change the coefficient of friction of the pad, so it grabs and slips a couple hundred times a second, causes squeal. The disc is thin so not rigid in bending, tailor-made to oscillate at its natural frequency.

A good local bike shop with someone that works on discs constantly, may have the answer.

Last edited by Duragrouch; 02-23-24 at 05:19 AM.
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Old 02-23-24, 05:16 AM
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Originally Posted by Duragrouch
I'm not a disc expert, I have no bikes so equipped. But no mention above regarding any pad alignment issues, but I don't know if any adjustment is possible there. Squealing on rim brakes is often caused by pad misalignment. A squeal comes from vibration, so something is oscillating very fast, especially for a higher pitch. For example, the pad/caliper could be deflecting, then snapping back, a couple hundred times a second. So rigidity of everything, mating angles, etc, all matter. Note: Car disc brake pads often came with an anti-squeal kinda rubber cement, that if I recall, was applied between the pad and caliper piston.
You can adjust the alignment of the whole caliper (pads are fixed relative to that) and usually have to, to get the pads clear of the rotor, so there’s not a lot of wiggle room there like there is with rim brake pads.
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Old 02-23-24, 07:17 AM
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If none of the above tips works there is a product called "Squeal Out" that works quite well. We use it in the shop often and it has never failed us. It is a bit pricey and can be hard to get at times but well worth the cost.
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Old 02-23-24, 07:31 AM
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I had some squealers and there was nothing I could do and I tried everything. Replacing the pads and rotors was the only cure. Disc brakes are great until they aren't. Then they are a pita. I am now very careful when working on or around them.
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Old 02-23-24, 06:46 PM
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Originally Posted by Kai Winters
If none of the above tips works there is a product called "Squeal Out" that works quite well. We use it in the shop often and it has never failed us. It is a bit pricey and can be hard to get at times but well worth the cost.
Squeeealll Out! sadly is no more. They have ceased to be! Sadly the company PV Bikeworks is not pining for the fjords they have snuffed it as far as I can tell. I think JBI sells a similar product though I haven't yet tried it but it looks close. I haven't found another alternative but I hope that someone at Park or Pedro's is working on it or some lube company?

In terms of cleaning rotors and pads road in alcohol take to a safe place and light them on fire and let them burn. I usually will do it twice and then spray one final time to cool down with more alcohol. I generally don't use soap and water on any of that so I don't risk contamination from other oils in the soap however if it was particularly dirty I might do that then soak it in alcohol and then burn it but usually the alcohol does the trick and if not Squeeealll out! would handle the rest.
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Old 02-26-24, 09:04 AM
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I have the Swiss Stop pads and it took several months of riding before they stopped "moaning"

wasn't really a squeal, and it was only on the first 1-2 applications of the brakes.

I suspect that enough wear had to occur to burn thru the glazing material and expose the abrazive pad materal.

Caliper alignment is important too.

On the race car there was a process for "bedding in" new pads after several laps, repeated stops to get the pads warm so they worked well.

I don't think bike brakes develop that much heat.

/markp
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Old 02-26-24, 12:10 PM
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Originally Posted by mpetry912
I have the Swiss Stop pads and it took several months of riding before they stopped "moaning"

wasn't really a squeal, and it was only on the first 1-2 applications of the brakes.

I suspect that enough wear had to occur to burn thru the glazing material and expose the abrazive pad materal.

Caliper alignment is important too.

On the race car there was a process for "bedding in" new pads after several laps, repeated stops to get the pads warm so they worked well.

I don't think bike brakes develop that much heat.

/markp
You would do the same sort of bedding in on a bike, typically doing hill repeats dragging the brakes. It helps quite a bit, my old shop had a perfect nearby hill that went nowhere but was steep and ended in a lower traffic spot. They also make a lovely machine now to help with that so you don't have to ride it but I remember it being expensive and you would need to be a shop or a high volume disc brake installer to need it.
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