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New(ish) bike, back brake becoming noisy as hell!

Adam_DT3Adam_DT3 Posts: 52
edited August 2010 in MTB workshop & tech
Picked up a genesis core 30 a few months back but the rear disk break is becoming increasingly noisy, so noisy in fact I am using it to make pedestrians move out of the way on the cycle path lol.

Really need to look into fixing it tho, but a total novice when it comes to disk breaks. When I lightly pull the trigger i get what can only be described as a v high pitched squeek, followed by a very loud drone noise when I apply full breaks. The break works fine regardless and the front works fine with no noise too.

Is this a common issue someone could help me with? or is this something I need to get the bike serviced for?

From Evans site, I have the following;

Front Brake:
Shimano BR-M575 hydraulic discs
Rear Brake:
Shimano BR-M575 hydraulic discs
Brake Levers:
Shimano BL-M575

http://www.evanscycles.com/products/gen ... e-ec021331

Posts

  • I would suspect brake pads have worn/been contaminated. Easiest way is to take them out and have a peek...
  • nicklousenicklouse Posts: 50,675 Lives Here
    have read of http://www.bikeradar.com/forum/viewtopic.php?t=12674934

    will give you some ideas.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • davildodavildo Posts: 162
    I had a very similar problem to this when I got my new bike.

    I'm not sure whether the shop set it up wrong but the caliper was not centred properly on the disc.
    This caused the pad and disc to glaze, which just gets progressively worse and noisier.

    Look at your pads very closely and how they line up to the disc. There should be a small gap each side but you should be able to see daylight. Then pull the lever looking VERY closely at the disc from above so that you can see whether it bends, even very slightly, when the pads squeeze in from each side tp grip it.

    To correct this you just have to release the bolts holding the caliper to the frame, pull the brake on hard and tighten the bolts whilst holding the brake. This should center the caliper, leaving the gaps as mentioned above and even braking from each side that does not bend the disk. You could spin the wheel at this point and look at the gap to see if your disc is bent.

    However, if the pads and discs are glazed, this will still not solve the problem. I ended up buying a new rotor and new pads. I then centered the caliper properly and hey presto, silent braking. Apparently you can sort out glazed pads and discs with a proper clean but I didn't have much luck trying this, hence new pads / rotor.

    Sorry if that all sounds a bit confusing. I've tried to describe how I sorted my brakes out as clearly as possible.

    Cheers,

    Dave.
  • mobilekatmobilekat Posts: 245
    I suffer from noisy brakes too, this is due to me being a tad heavy on my brakes!- so the further down a hill I get the louder the noise.

    I blame living on the edge of the moors, which means we often have 2-3 mile descents down country lanes with poor visibility.- too many tight bends- with cars gunning it to come up the hill!

    If I am being good and remember to stay of the brakes, not over heat them and dont panic the noise is much better!

    But its a good way of moving pedestrians!!!
    Wheeze..... Gasp..... Ruddy hills.......
  • Paul 135Paul 135 Posts: 92
    dont worry :) being new you will be taking the glaze off the pads and cause the pads a rubbing on the disks they vibrate and make a noise its known as harmonic vibrations to nothing you can do really but it can (should?) sort itself out :)
  • ive had this problem easy to fix de-glaze the pads by taking the glaze off the pads with a fine file, then clean the disc with petrol, after this they will be as good as new, done this numerous times works a treat, better than buying new pads every time they glaze over and also a lot less noisey :D
  • Adam_DT3Adam_DT3 Posts: 52
    Thanks for all your advice, I prob shouldn't take the brakes apart by myself so if it doesnt sort itself out then I will prob take back to evans for a service. Can anybody recommend an online guide or something to show disk break maintenance for times when im feeling braver?
  • I'm not sure whether the shop set it up wrong but the caliper was not centred properly on the disc.

    Sorry got to disagree, calipers by their very nature are self-centering. The pressure in the brake fluid is the same throughout the caliper and if one piston/pad is slightly further away when initially fitted it will centre itself on first application of brakes. Same as car brakes which I've been working on for years.

    Try the automotive trick of putting a very small amount of copaslip or the like on the rear of the pads (the metal bit, not the braking surface !).

    This is done on car brakes every time replaced, and works wonders on bikes as well. Stops all manner of squeeks, and vibrations. Also degalze the pads as suggested above.

    Cheers
  • Bar ShakerBar Shaker Posts: 2,313
    Er, bike callipers normally only have one piston so nothing like car brakes at all.

    The noise is glaze but not on the pads, the disc grooves/slots clean the pads. Clean the disc by sanding with fine grade wet and dry paper moving the paper in a radial pattern towards the centre and back out. Never sand in a motion along the braking surface.

    Once you have a fine dull sheen on the disc it's time to start again. Re centre the calliper and then rebed the pads in. 20 braking efforts from running to walking pace (not to a stop) then 20 stops from 15mph to walking pace, applying more power. Finally repeat the last 20 with full power applied to the lever.

    The braking power will increase over the next few uses and any noise from residual glaze will disappear after the first few uses.
    Boardman Elite SLR 9.2S
    Boardman FS Pro
  • Hi,

    I was refering to OP's calipers "Shimano BR-M575 hydraulic discs" which are twin pot and just like car brakes. :D

    Didn't mean single pot or mechanical calipers. (Although copaslip still works)

    Sorry for confusion.

    Cheers
  • Bar ShakerBar Shaker Posts: 2,313
    :D oops, quite right. Good bedding in is really important so you get a uniform film of resin on the disc, it's the resin that will give you good uniform stopping power.

    Copperslip will help the pads from jarring at angles to the disc. As St George would say, use sparingly so it doesn't get on pad faces.
    Boardman Elite SLR 9.2S
    Boardman FS Pro
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