Xt M785 Brake Noise/Dragging?

maccasparks
maccasparks Posts: 4
edited May 2015 in MTB workshop & tech
Howdy - when I ride down flowing trail with sweeping turns my rear brake makes a horrible pad on rotor noise after I have braked and exiting the corner. If I only use the front it does not happen. I suspect the lever is too slow to release the pressure in the line and maybe combine with a bit of rear flexing (Stumpy Evo 29) I'm getting the noise. Brakes work very well and wheels spin long and freely while on the stand. I have bleed the brakes and replaced Shimano Oil and Pads - old oil was quite grey/black but after two weeks on fresh it has made no difference. Bike was a Ex Demo only six months old but maybe done a bit of work - everything is great! Tonight I swapped callipers front to rear but not going to be on trail for a while so not sure if that's effected anything. The lever does look slightly sluggish to return to normal position compared to the front lever. Any hot tips?

Comments

  • oxocube1
    oxocube1 Posts: 651
    It sounds like rear wheel flex as it happens to you in corners. Is it a QR on the rear?
    2016 Banshee Rune

    2012 Nukeproof Mega
    2011 Haro Flightline Expert
    2010 Spesh FSR XC Pro
  • The Rookie
    The Rookie Posts: 27,812
    Check for a slightly sticky piston at the rear, watch how they retract when you release the brake, if one is sticky then remove the pads and push that piston out a bit (squeeze the level while holding the good piston in), clean the piston with some fresh oil on a cotton bud or similar, push back in, repeat, clean thoroughly to remove excess oil then refit.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • maccasparks
    maccasparks Posts: 4
    Axle is 12x 142 . I will wait and see it still does it after calliper swap to confirm sticky piston. Cheers
  • maccasparks
    maccasparks Posts: 4
    UPDATE : Hit some sweet trails tonight and noise is gone so sounds like sticky piston was the go. Just to be sure I removed top cap of lever and cleaned some more blackish crap off the parts inside , then bleed again. Lever seems faster to return .Also got the cotton buds out and cleaned the pistons as described above. Front is working well but will give it the same treatment after weekend - got two days riding with bit of camping to get too.
    Cheers for the advice folks!

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