Screaming brakes

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Screaming brakes

Postby fozzie » Wed Jul 10, 2013 2:13 am

After some advice for a friends bike I'm attempting to fix. The bike is a cube fitted with shimano brm446 callipers. He's had the bike from new, about 12 months, he keeps it in good service. He made the mistake of spraying some gt spray near the brakes and buggered them up, so replaced pads and cleaned discs. This is when the screaming brakes started, god it's loud!, front and back. So pads out, new 180 discs, full degrease, new pads, 10 min bed in ride and all seemed ok. Next ride, banshee scream! So he's left it with me to look at, I've stripped both callipers and found the rear one is leaking from piston, so new one needed, I've bled and put new pads on the front, screams when slight pressure is put on, but performs awesome stoppies when full pressure. It's baffling me as to the reason it screams. My Hayes soles are silent! :) any ideas to on the noise?
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Re: Screaming brakes

Postby schwim » Wed Jul 10, 2013 7:53 am

Heya fozzie :)

In my experience, once you've removed the residual material on a rotor by either replacing, cleaning or sanding it, more than the normal bed time is required to apply enough pad material back onto the rotor so it doesn't howl. The sound is caused by vibration of a grabbing brake causing pad material to be applied to the rotor in pulsing waves. Once it's begun, it's almost impossible to reverse without cleaning or sanding and will just keep getting worse.

From a tech article:

As the brakes go through the break-in period, they don't begin to stop with authority until some of the brake pad material is deposited on the rotor as the two components bed together. If the pad cuts through this layer or the layer is laid down irregularly by an improper break-in interval, the pad jumps a tiny bit as it hits a damaged area, digs in, jumps a bit and then digs in again a short distance beyond. The sequence creates an oscillation which continues onward, creating a microscopic series of waves around the circular braking track. Once the pattern is created, the rotor essentially becomes a steel recording disc that is programmed to squeal - and it can't be erased simply by switching to new pads. Brake squeal is most commonly caused by a weak initial break-in period, with the introduction of impurities like chain lube or chemical bike cleaners to the braking surfaces as a close second.


I would suggest a longer seating period. Because I don't have the patience to do it myself, I just combine the process with my rides. When it's time to brake, do it with as much pressure as possible without breaking the tires loose and then get off of them completely. The absolute worst thing you can do is to apply light pressure over an extended period of time.

Since it's howling on you already, I would suggest sanding the surface lightly so you have a fresh start then get some really good hard braking cycles in. I bet that will get rid of your problem.
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Re: Screaming brakes

Postby JacksPerson » Wed Jul 10, 2013 9:34 am

Since it's howling on you already, I would suggest sanding the surface lightly so you have a fresh start then get some really good hard braking cycles in. I bet that will get rid of your problem.


Everything Schwim said, but I would also add:

- I have found it best to lightly sand the rotors in a circular pattern to avoid making anymore grooves length wise in the rotors.

- Make sure all the fasteners are tight too, if the rotor fasteners are loose it can sing too.
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Re: Screaming brakes

Postby SCHucker » Wed Jul 10, 2013 12:23 pm

fozzie wrote:He made the mistake of spraying some gt spray near the brakes and buggered them up, so replaced pads and cleaned discs. This is when the screaming brakes started, god it's loud!, front and back.

What did he clean the disc with? Standard rubbing alcohol is the best for cleaning disc's, but if they were cleaned with chemicals like brake cleaner, then you will have issues then. The best to do here is to lightly sand the rotor on the rim (where the pad contacts the rotor in full). Clean it very well prior and after sanding with rubbing alcohol. Would not hurt to touch up the pads as well (very lightly sanding), then cleaning them as well with alcohol as well.

The best way to burnish (initial break-in period or when just changing pads) your pads and disc correctly is to brake harder, but not enough to lock up the front tire and either do a hard stoppie or even endo. Just be harder on the applying to better burnish them in bro. It will take a couple of good hard rides to completely burnish them in correctly.

Good luck!
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Re: Screaming brakes

Postby fozzie » Wed Jul 10, 2013 12:32 pm

Thanks for the help guys. Ill rub the disc and use some alcohol on them, new pads too. To be honest he's a big girl (no offence to the girls out there!) when it comes to braking and riding :) he's ordered a new rear calliper to replace to seized and leaking one.
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Re: Screaming brakes

Postby fozzie » Sat Jul 13, 2013 8:09 am

Front bled, disc cleaned and sanded, pads sanded, 10 12mph brake slams, screaming gone! Now rears to be done
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Re: Screaming brakes

Postby schwim » Sat Jul 13, 2013 8:51 am

Enjoy the newfound silence :)
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Re: Screaming brakes

Postby SCHucker » Sat Jul 13, 2013 1:05 pm

fozzie wrote:Front bled, disc cleaned and sanded, pads sanded, 10 12mph brake slams, screaming gone! Now rears to be done

Awesome!!! :mrgreen:
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Re: Screaming brakes

Postby fozzie » Sat Jul 13, 2013 6:46 pm

schwim wrote:Enjoy the newfound silence :)


I've still got to put up with his whining! But I can always speed up and leave him behind ;)
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Re: Screaming brakes

Postby SCHucker » Sat Jul 13, 2013 7:46 pm

fozzie wrote:I've still got to put up with his whining! But I can always speed up and leave him behind ;)

+++1 :lol: :lol: :lol: :lol: :mrgreen:
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Re: Screaming brakes

Postby schwim » Sat Jul 13, 2013 7:47 pm

Man, that must be nice. Luckily for me, I'm always the one that's waaaay in the back. Its very serene when you're the slowest Guy around.
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Re: Screaming brakes

Postby maddslacker » Sun Jul 14, 2013 9:46 pm

schwim wrote:Man, that must be nice. Luckily for me, I'm always the one that's waaaay in the back. Its very serene when you're the slowest Guy around.

I'll challenge you for the slowest rider status. Jeff and Mtbgreg can confirm my slowness. :lol:
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Re: Screaming brakes

Postby fozzie » Mon Jul 15, 2013 2:17 am

schwim wrote:Man, that must be nice. Luckily for me, I'm always the one that's waaaay in the back. Its very serene when you're the slowest Guy around.


I get the crazy man face and just steam off like a nutjob :) it's funny because he has all the latest kit on his bike, I used to ride a 10year old Saracen with spring shocks! My latest bike is home built, carbon frame rigid, lightweight missile
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Re: Screaming brakes

Postby schwim » Mon Jul 15, 2013 9:03 am

maddslacker wrote:
schwim wrote:Man, that must be nice. Luckily for me, I'm always the one that's waaaay in the back. Its very serene when you're the slowest Guy around.

I'll challenge you for the slowest rider status. Jeff and Mtbgreg can confirm my slowness. :lol:


You're just going to be sad when you find out that you're only the second slowest rider on the site.

My dad always used to say "The second slowest is the first winner." Or something of that sort. I couldn't really hear him well because he was so far ahead of me.
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Re: Screaming brakes

Postby maddslacker » Mon Jul 15, 2013 9:23 am

I'll bring my secret weapon in the slow dept: the fat bike. :twisted:
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