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Brakes work better as a horn
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Need some help with my disc brakes. Shimano resin pads. Rear brake works fine. Front brake is giving me trouble. To start, it has about half the stopping power of the rear brake. But when I try to really use it, it makes a sound like an air horn. And when starts to honk it brakes even worse.

I have tried isopropyl alcohol, acetone and sandpaper on both the pads and rotors (and all three at once). Nothing seems to make any difference. I have tried gentle and aggressive bedding. Both cases the rotors are quickly covered with a dark powder.

The only bright side is I have a little something extra when people can't hear my bell. Scared the crap out of a teenager yakking on the phone in the middle of a bike path.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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replace the pads, to start with.

is the caliper tightened down? Is a piston seized?

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Re: Brakes work better as a horn [JasoninHalifax] [ In reply to ]
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JasoninHalifax wrote:
replace the pads, to start with.

is the caliper tightened down? Is a piston seized?
The pads are only a couple of months old with hardly any wear. Worked fine for the first month. Started honking after a rainy ride.

I'll check the piston.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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Thinking about it. the acetone probably broke down the pad material and now they're contaminated.

Swimming Workout of the Day:

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Re: Brakes work better as a horn [torrey] [ In reply to ]
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Well, brakes ARE a means of expressing fear

"What's your claim?" - Ben Gravy
"Your best work is the work you're excited about" - Rick Rubin
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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I had a very similar experience this weekend but with the sintered metal pads. Pads have been excellent and quiet forever but riding down a steep hill with switchbacks and a shitty road surface i may have overheated them and for the rest of the ride the front brake was squealing extremely loudly with a significantly reduced braking power. Especially when trying to brake hard, it suddenly became very loud and less effective. It was not raining but it was cold and humid, however.

I took the pads out and cleaned them with isopropyl alcohol to remove all the black dirt on them. Only done one ride since then - zero squealing and brakes worked fine but that ride was flat and didn't require hard braking. So hopefully the problem will be solved. If not, I'll replace the pads.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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I thought maybe this was a post about cantilever brakes. They pretty much signal to the rider in front of you that you're going to hit them.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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torrey wrote:
JasoninHalifax wrote:
replace the pads, to start with.

is the caliper tightened down? Is a piston seized?

The pads are only a couple of months old with hardly any wear. Worked fine for the first month. Started honking after a rainy ride.

I'll check the piston.


If the piston moves free, check that the rotor is true. It could make some sound, especially if the caliper bolts are a little loose.

Then, try new pads (clean the rotor again first!) If they honk as well, no idea.

I take it your bedding in procedure is fine and not coming to a full stop, right?
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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I'd try new pads. A single drop of contaminant (such as any kind of oil) permanently ruins resin pads. Make sure to wipe out the calipers and then reclean the rotors when you change the pads or you might end up right back where you started.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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torrey wrote:
The pads are only a couple of months old with hardly any wear. Worked fine for the first month. Started honking after a rainy ride.

I saw a lot of this back at the last shop I worked for. The day after a rain, especially if it hadn't rained in a while, people would be coming in complaining that their disc brakes were making lots of noise and/or weren't stopping anymore. The oil and anti-freeze that accumulated on the asphalt would float to the top of the puddles when it rained and get splashed on the rotors when people rode through, and then the pads got contaminated the first time they used the brakes.

"I'm thinking of a number between 1 and 10, and I don't know why!"
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Re: Brakes work better as a horn [Warbird] [ In reply to ]
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Gee disc brakes sound awesome....
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Re: Brakes work better as a horn [dunno] [ In reply to ]
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When you are running 42s on a gravel bike and riding through creeks they are pretty awesome. Don’t know why anyone would put them on a road bike though.
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Re: Brakes work better as a horn [Warbird] [ In reply to ]
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Sometimes you can save these pads by hitting them with an open flame like a propane torch or holding them over a gas stove burner
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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Another thing I’ve done successfully to rescue fouled pads &/or rotors, is pour some boiling water on them.

We have one of those electric kettles for heating water for tea & coffee, it works like a charm for this.

It’s not hot enough to damage the frame or any components, but might be enough to wash away whatever is causing the flock of wild geese to follow you around.

Worth a shot.
YMMV.


float , hammer , and jog

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Re: Brakes work better as a horn [Murphy'sLaw] [ In reply to ]
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Squirt some water on the caliper, soaking the pads whilst you wheel it along with the brakes on or squirt them while you ride.
If this does not fix it, buy new pads, clean rotor with alcohol and it will be fixed.
DO NOT SAND your rotors.
This only creates scratches for contaminates to hide in.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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Unscrew the brake's disc. Grease screws generously. Screw back the disc and firmly tighten the screws. It will not change the breaking power obviously, but should fix the horn issue.

Source: years of experience with my MTB.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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Here is my unofficial cheat for when new pads squeal on disc brakes. Keep in mind Shimano will probably tell you don't do this but its worked every time for me so far.

Remove pads from caliper
Place the pads face up on your driveway or other heat/flame proof surface
Use a butane torch on the pads for 10-15 seconds to bake them and burn off any contaminants (wear eye protection)
Remove the glaze on the pad with sandpaper/emery cloth.
Clean the rotor with isopropyl
Install pads
Bed pads
Last edited by: SiRcivic27: May 30, 19 8:46
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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So, I swapped out the pads and everything worked great for a week or two. I thought the problem was solved.

I had a month off the bike and rode it again for the first time today. Same problem as before.

So the pads are not the root cause. I didn't ride in rain or any of that. I don't think it is the rotors or caliper mounts, or it wouldn't have temporarily fixed with new pads. My guess is that I have a slow leak in the caliper somewhere which is contaminating the pads.
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Re: Brakes work better as a horn [torrey] [ In reply to ]
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Wife only does a small amount of recreational riding (never in the rain) and had an issue that cleaning pads/rotors didn't fix. One trick that did work (keeping wheels mounted in frame) was to loosen the pad mounting bolts, apply brakes, tighten mounting bolts. Has been OK for a few months now. I think it was something like toe-in on rim pads, I think in our case the pads weren't parallel to the rotors and causing a squeel.
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