Screeching disc brakes

Jerry185
Jerry185 Posts: 143
edited July 2018 in The workshop
Five year old Boardman hybrid with city commuting. Shimano brm 615 disc brakes
Recently, brakes started howling. Took out pads and cleaned; gunk out of works and rubbed down rotors. No joy
Bought new pads - sort of ok.
Few days later it rained, now screeching brakes. Note, no loss of braking power.
Talked to LBS . He said it was leaking calipers . £78 for new calipers.
Thought - why would leaking oil cause 200 decibel noise on braking?
Thoughts please.

Comments

  • kajjal
    kajjal Posts: 3,380
    Rim brakes are rubber on aluminium rims, disc brakes are metal on metal and a lot more powerful.

    This is why any oil on disc brakes stops them working and you get a really nasty screeching noise. In really bad cases the whole bike can vibrate.
  • The Rookie
    The Rookie Posts: 27,812
    Most screeching is caused by a resonance, that can be triggered by a fluid leak, or damp in the pad, or rain, or slightly glazed pads... or a host of other reasons, if the brakes are otherwise working fine, just keep on riding, a few good hard stops often helps, especially if you drizzle some dry dust onto the pads before doing them.
    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.
  • greenamex2
    greenamex2 Posts: 272
    Probably leaking.

    Had this twice recently -

    Once where the bleed valve hadn't been tightened properly by the LBS...trashed two sets of pads and one disc before resolved.

    Currently on the hybrid where BOTH front and rear calipers simultaneously started leaking via a piston...awaiting confirmation of a possible warranty claim as they have only done 700 miles. Picked by pressure testing the systems...wasn't obvious otherwise.

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