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Discussion Starter #1
Hi,

When braking from speed (either stopping from 70mph) or downhill to a stop - there is a rotational ‘scraping’ noise on the front (I think nearside brake - although could be both). Pads have 5mm and discs are fine. It only seems to be when they’d be at their hottest (i.e. coming to a stop after sustained braking downhill). Then when brakes are released - this rotational noise continues relative to the wheel speed. As soon as I go over 20+ mph it goes away again. There’s no sponginess or fading and the car stops well.
It doesn’t happen after ‘normal’ braking i.e. stopping from 30mph at lights.
The brake fluid will need changing soon-ish (b.p. 219°C) but I don’t think that would cause this. If that was boiling surely you’d have loss of pedal feel?

Any ideas or guidance would be appreciated. Thanks.
 

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It might be a sticky caliper. Only thing you can realistically do is have a good inspect and perhaps try to free the calipers manually.
 

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I bet this is the tin stone guard behind the disc making contact, it has all the marks of being that and I've had it happen on loads of cars.
The noise isn't going away after a certain speed, it's just the frequency and other noise means you can't hear it any more.
It's an easy fix with the wheel off, just literally bend it away from the disc.
It's something I do on any car when I have the wheels off as a matter of routine.
You can even do it with the wheel on, if the alloys have big enough gaps to get your hands in.
 

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Discussion Starter #4
I bet this is the tin stone guard behind the disc making contact, it has all the marks of being that and I've had it happen on loads of cars.
The noise isn't going away after a certain speed, it's just the frequency and other noise means you can't hear it any more.
It's an easy fix with the wheel off, just literally bend it away from the disc.
It's something I do on any car when I have the wheels off as a matter of routine.
You can even do it with the wheel on, if the alloys have big enough gaps to get your hands in.
Thanks both,
Also I have just noticed a squeak when moving very slowly (1mph) any faster and it stops - without brakes applied - does this suggest sticky calliper?
 

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Thanks both,
Also I have just noticed a squeak when moving very slowly (1mph) any faster and it stops - without brakes applied - does this suggest sticky calliper?
That sounds like a pad lightly touching the disc.
Not necessarily a 'sticky caliper', could just be dust build up etc.
If it were me and the pads were in good nick, I'd just take the pads out, clean up everything and apply new brake specific grease to the backs of the pads (not copper grease).
Check the anti rattle shims were still in place, they can fall out/break up.
Sorry, I've no idea how competent you are in home mechanics, so I don't know if these terms will mean anything.
 

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Thanks both,
Also I have just noticed a squeak when moving very slowly (1mph) any faster and it stops - without brakes applied - does this suggest sticky calliper?
Could be. Short of having a good look at the brakes and assocoated parts you are not going to diagnose the problem while sitting behind your keyboard. There is just one more thing you could try. Get it going fast in reverse and stand on the brakes - try it two or three times. Sometimes a stone gets wedged in there and this could ping it out.
 

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Discussion Starter #7
I've had a look and the disc is slightly lipped (all the wheels are - but the NSF is the most pronounced). However there's still a lot left on the discs and the pads have >5mm so I don't really want to replace them if I don't have to. Could a slightly lipped disc cause this.
- But I'm thinking if it was this it would happen all of the time - not just when they're red hot from stopping downhill?

Thanks all
 

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Metal expands when "red hot"
So it's perfectly feasible whatever problem you have is only arising when the metals expand and something starts touching something else.
 

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The lips you mentioned often are just large enough to scrape on a caliper holder bracket, or hub.
Hold a big flat screw driver against the lip, while rotating the disk by hand until all loose lip is scraped off.
Especially the inside where there will be more rust.
Use of 60 grade paper, from a belt sander for ex, will also smooth off the lips.

Best results are achieved by removing the discs and using a grinder. Even a hand file is effective.
 

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Discussion Starter #11
The lips you mentioned often are just large enough to scrape on a caliper holder bracket, or hub.
Hold a big flat screw driver against the lip, while rotating the disk by hand until all loose lip is scraped off.
Especially the inside where there will be more rust.
Use of 60 grade paper, from a belt sander for ex, will also smooth off the lips.

Best results are achieved by removing the discs and using a grinder. Even a hand file is effective.
Will give this a go at the weekend
 

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Check the brake discs for corrosion on their outer edges. My car had a similar issue and once I'd cleaned the flaking rust off with an old chisel and wire brush it stopped.

Also, I recently replaced my front discs and on the first drive after there was a rubbing noise coming from the offside front. It turned out to be the brake disc shield rubbing slightly on the inner edhe of the disc. I cleaned it up and bent it slightly, put it all back together and went for a drive and the noise was gone.
 

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I had this metallic scraping on mine when the brakes got really hot, even after replacing them all with genuine parts. It ended up being the steel brake pad clips touching the brake disc when they get warm, I removed them and ground a portion out in the middle to increase clearance.
 
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