New bike - scraping noise from front disc brake

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poorlittlefish
Posts: 11
Joined: 3 Jul 2019, 9:54am

New bike - scraping noise from front disc brake

Postby poorlittlefish » 17 Jul 2019, 9:25pm

So after finding out from the knowledgeable folks on this forum that it wouldn't be cost-effective to change the brakes on my old bike, I ordered a new one with disc brakes. I had to assemble a few bits myself, including putting on the quick release front wheel on, which all seemed fine. However, while the back wheel turns smoothly, the front wheel is making a scraping sound from where the brake is and it sounds like metal upon metal. I tried a quick fix I saw on YouTube (loosening the bolts of the arm, applying the brake fully then tightening the bolts before releasing the arm) but if anything it's made the noise worse.

Do the brakes just need to bed in a bit or should I be contacting the company to complain? They were supposed to have checked the bike over and set it up properly before sending it to me - thanks.

Brucey
Posts: 35906
Joined: 4 Jan 2012, 6:25pm

Re: New bike - scraping noise from front disc brake

Postby Brucey » 17 Jul 2019, 9:44pm

three options

1) fix it
2) send the bike back
3) go to the bike shop

If you don't know how to fix bikes then I'd suggest that you don't buy a mail order bike.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

pwa
Posts: 10439
Joined: 2 Oct 2011, 8:55pm

Re: New bike - scraping noise from front disc brake

Postby pwa » 17 Jul 2019, 9:52pm

Is there any way one of the pads could have been loose and come out while the wheel wasn't in? Is that possible?

mattsccm
Posts: 2729
Joined: 28 Nov 2009, 9:44pm

Re: New bike - scraping noise from front disc brake

Postby mattsccm » 17 Jul 2019, 10:09pm

Quick options.
Put bike on wheels and open QR if it has them. Close Qr. That should ensure wheel is in straight. Now check caliper is straight . This means re-doing what you have done. You will find that this is a knack that gets easier.
Check pads correctly set up. Maybe you have knocked them at some point. Discs have plenty of scope for minor cock ups if you don't have experience.
How many miles. New pads can be noisy as can new discs.

ElCani
Posts: 155
Joined: 5 Mar 2015, 11:24am

Re: New bike - scraping noise from front disc brake

Postby ElCani » 17 Jul 2019, 10:12pm

Discs often scrape and the fixing method you describe doesn’t always work, as you discovered. It’s often possible to align the caliper by eye, ensuring the pads are parallel with the disc and equidistant from it, then tighten the bolts. This might take a few tries and you might find the caliper wants to move as the bolts are tightened. Also, some caliper designs mean it’s hard to properly see what you’re doing.

If you don’t manage to get it to work, you can also try sliding cardboard spacers between disc and pads, then applying the brakes and tightening the bolts.

Good luck!

Debs
Posts: 523
Joined: 19 May 2017, 7:05pm
Location: Powys

Re: New bike - scraping noise from front disc brake

Postby Debs » 17 Jul 2019, 10:15pm

Check you haven't got a bent rotor.

ElCani
Posts: 155
Joined: 5 Mar 2015, 11:24am

Re: New bike - scraping noise from front disc brake

Postby ElCani » 17 Jul 2019, 10:50pm

Debs wrote:Check you haven't got a bent rotor.


Yup, good point which I forgot!

rmurphy195
Posts: 1424
Joined: 20 May 2011, 11:23am
Location: South Birmingham

Re: New bike - scraping noise from front disc brake

Postby rmurphy195 » 17 Jul 2019, 11:24pm

What brakes are they? Avid, Spyres, cable, hydraulic?

Once you let us know what they are, users of the specific type of brake will be able to tell you if/how they cured the noise.

Oce set up and bedded in, often a case of careful adjustment, the method for which depends on which type you have fitted.
Brompton, Condor Heritage, creaky joints and thinning white (formerly grey) hair
""You know you're getting old when it's easier to ride a bike than to get on and off it" - quote from observant jogger !

poorlittlefish
Posts: 11
Joined: 3 Jul 2019, 9:54am

Re: New bike - scraping noise from front disc brake

Postby poorlittlefish » 18 Jul 2019, 7:11am

They're cable disc brakes on a Merida mountain bike. When I spin the wheel the rotor seems to spin in line, but the noise does seem to be for about half a rotation rather than constant.

rfryer
Posts: 675
Joined: 7 Feb 2013, 3:58pm

Re: New bike - scraping noise from front disc brake

Postby rfryer » 18 Jul 2019, 7:33am

On most cable disc calipers, only one of the pads moves. So after setting up the calipers up as describe, you might need to retract the static pad to prevent it from contacting the disc. I don't know it that is an option on all calipers; it's certainly "a thing" on BB7s.

Eyebrox
Posts: 253
Joined: 5 Aug 2015, 8:56pm
Location: Ayrshire

Re: New bike - scraping noise from front disc brake

Postby Eyebrox » 18 Jul 2019, 7:43am

Just go out cycling. Give the brakes a good workout on a hilly path. The pads will wear down slightly in the area which is rubbing.

mattsccm
Posts: 2729
Joined: 28 Nov 2009, 9:44pm

Re: New bike - scraping noise from front disc brake

Postby mattsccm » 18 Jul 2019, 7:58am

Also consider the fact that discs are often not perfectly straight. price of them doesn't seem to matter. If set up with close clearances you will get rub. The fact that it only happens with half a revolution suggests that this maybe worth investigating.

slowster
Posts: 980
Joined: 7 Jul 2017, 10:37am

Re: New bike - scraping noise from front disc brake

Postby slowster » 18 Jul 2019, 10:22am

If the video you saw on Youtube was the one from the Park Tool website, that is fairly thorough. If not, suggest you follow the guidance in the Park one:

https://www.parktool.com/blog/repair-help/mechanical-disc-brake-alignment

dobbo800
Posts: 39
Joined: 29 Sep 2016, 12:23pm

Re: New bike - scraping noise from front disc brake

Postby dobbo800 » 18 Jul 2019, 10:35am

It's not unusual for new pads to need 'wear in' time. You get the same issue with motorcycles. One thing you might want to check though - some braking systems use a metal 'spring' to hold the pads back against the pistons and off the rotor. Make sure these springs are installed correctly and are not touching the rotor.

Someone higher up the thread suggested using a cardboard spacer between the pad and piston. Don't do this. For one thing, it's a bodge on an essential system and, well, cardboard does not fare well in the rain.......

Brucey
Posts: 35906
Joined: 4 Jan 2012, 6:25pm

Re: New bike - scraping noise from front disc brake

Postby Brucey » 18 Jul 2019, 12:24pm

dobbo800 wrote:
Someone higher up the thread suggested using a cardboard spacer between the pad and piston. Don't do this. For one thing, it's a bodge on an essential system and, well, cardboard does not fare well in the rain.......


that suggestion was made for setting up purposes; mechanical disc calipers need a clearance vs the fixed pad and this is one way of setting it.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~