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Discussion Starter · #1 ·
Apologies If this has been asked.

Im running hope m4s and the rear brakes tend to have a low scratching sound that is a little irritating. (its different to the high pitched screeching sound that most experience). The sound only happens after I pull the brake a lot on downhills and becomes normal again after a period of time.

Im running metallic brake pads and am wondering if this is related to heat?

thanks.
 

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IS it a "Schwing" type noise? If so, could mean you need a good bleed, could be that there's air in the system and when it gets heated up and expands it's pushing the pistons out some and then when it cool, it contracts and everything is good again.
 

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Discussion Starter · #4 ·
IS it a "Schwing" type noise? If so, could mean you need a good bleed, could be that there's air in the system and when it gets heated up and expands it's pushing the pistons out some and then when it cool, it contracts and everything is good again.
yes. similar. But not that high pitched but is a low, course, rough metallic rubbing noise. The noise is like the amplified noise you get when you rotors rub on the pads when misaligned.
 

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One thing to check caliper alignment. If the caliper is not parallel to the rotor, the leading or trailing edges of the pads might brush the rotor making a tsinging or clicking sound. It can change as things heat/cool while riding.
 

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Discussion Starter · #6 ·
One thing to check caliper alignment. If the caliper is not parallel to the rotor, the leading or trailing edges of the pads might brush the rotor making a tsinging or clicking sound. It can change as things heat/cool while riding.
they are parallel but when i spin the rear wheel, the rotor is sometimes closer to the left pad, some times closer to the right.
 

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they are parallel but when i spin the rear wheel, the rotor is sometimes closer to the left pad, some times closer to the right.
Sounds as though the rotor is just a little off true. You can usually gently bend it back without a tool.
yep. rotor shouldn't be waving around in there. it should be as straight as possible. expansion/contraction from heat absolutely can cause a change in a rotor's warp that resolves some when it cools.

^^^yes. Try not to contaminate the rotor (or pads) with oil, grease, or fingerprints when you do this.
a clean, dry rag or paper towel works fine for me.

not a seruous problem tho is it?
disc brakes work best with high precision setup so that the calipers are square to the rotor (the pads are perfectly parallel to the rotor) and that the rotor is true (the gap between pads/rotor doesn't change). If the calipers aren't square to the rotor, and if the rotor is out of true, you'll have a reduction in performance. It's pretty simple in theory, but some people are not good at setting up disc brakes.

My understanding is that the setup process for Hopes is a touch different than what's usually recommended by other brake manufacturers.
 

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Discussion Starter · #11 ·
Sounds as though the rotor is just a little off true. You can usually gently bend it back without a tool.
How do I bend It back as I am not sure how much force to use and I am scared that I might bend the rotor itself. I have a IS mount so adjusting the brake caliper position is not possible
cheers mate
 

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Discussion Starter · #13 ·
[QUOTE

My understanding is that the setup process for Hopes is a touch different than what's usually recommended by other brake manufacturers

Hi, can you please give a simple outline of how to true the brake rotor? I have pliers and an adjustable wrench that I may use to bend it.
 

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IS mounted calipers can be aligned using shims. Back in the day they were supplied with a pack of shims that typically look like very thin washers* that you use to space the caliper inboard of the frame or fork mount.

They’re a bit fiddly to set up but simple, cheap and effective.

I’d try straightening* the rotor first if it is obviously wobbling

Steve

They can be “fork shaped” and just push over the bolt without fully undoing it which is easier to set up.
 

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I use a 6" crescent wrench which has smooth jaw surfaces that won't scratch rotor. I do it with wheels still on bike. Adjust wrench so it's snug but easy to slip over the rotor and slide it all the way into rotor. Then gently bend in areas that show a slight wobble (do it 180 deg away from caliper). You want to focus on bending the whole radius of rotor from center to outer diameter so any bend is a smooth transition. Start with gentle pressure and check for true after each attempt. Usually any bends are very small so it does not take much to true it up.

I hit it with a spray can of auto brake cleaner when done to clean off any contamination.
 
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