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Permanently squealing RS785 disc brakes

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  • March 16, 2017 at 12:32 pm #26892
    stub

    I wonder if anyone has experienced this or something similar and can shed some light on this for me

    I’ve got a cyclo cross bike with the Shimano RS505 shifters and RS785 hydro calipers. When I first set them up, everything is fine. I go through phases of not using the bike a lot (tend to ride the road bike more often as I’m a fair weather cyclist), yet when I do, I find the brakes squeal terribly – almost like there is oil all over the rotors, front and back. Around christmas time I re-bled everything, and fitted new pads and rotors. I used the bike quite a bit then and everything was fine. The front brake has however got noticably soft (The pad is quite worn), yet I though it should self-adjust?

    I’ve just got the bike out after six weeks or so of non-use and gone to check it over – the brakes squeal with the tiniest pressure again. I can’t see any signs of leaks, there is no sign of oil anywhere, so I’m at a loss to explain it.

    Can anyone shed any light?

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  • March 17, 2017 at 4:14 pm #889007
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    DaveE128
    risoto wrote:
    Sorry, but that  is why I absolutely hate disc brakes. I got some mechanical Avid BB7 brakes, so no fluids, and they are ALWAYS noisy – from the very beginning I bought the bike. Everything has been cleaned and adjusted several times. Goes away for a few rides. Then squeling terribly again. This happens in the dry  and the wet. I keep my bike clean and still..I am conviced that  the slightest dirt on rotors provoke it. When I clean them with alcohol it goes away for a while=1-2 rides. You can’t even see that the rotors are ‘dirty’ enough to provoke anything. I have never had a problem with caliper brakes. In the future I will avoid disc brakes like the plague! Same thing happened with my first bike with hydrolic disc brakes. that was Shimano and just as noisy.

    Are you using any kind of spray lube, polish, WD40/GT85 etc on the bike? You really want to avoid getting these on disc rotors.

    March 17, 2017 at 3:26 pm #889005
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    risoto

    Sorry, but that  is why I

    Sorry, but that  is why I absolutely hate disc brakes. I got some mechanical Avid BB7 brakes, so no fluids, and they are ALWAYS noisy – from the very beginning I bought the bike. Everything has been cleaned and adjusted several times. Goes away for a few rides. Then squeling terribly again. This happens in the dry  and the wet. I keep my bike clean and still..I am conviced that  the slightest dirt on rotors provoke it. When I clean them with alcohol it goes away for a while=1-2 rides. You can’t even see that the rotors are ‘dirty’ enough to provoke anything. I have never had a problem with caliper brakes. In the future I will avoid disc brakes like the plague! Same thing happened with my first bike with hydrolic disc brakes. that was Shimano and just as noisy.

    March 17, 2017 at 12:26 pm #889003
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    stub

    Thanks for all the responses

    Thanks for all the responses – reading through I’m convinced that it is the pistons leaking.

    I think I’m going to have to bite the bullet and remove the calipers and send them back. Only problem is the place I bought them from is no longer trading so I’ll have to try and persuade my local LBS to send them back for me….

    March 17, 2017 at 9:41 am #889001
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    kev-s

    Deffo leaking caliper

    Deffo leaking caliper

     

    Had this on a shimano zee brake caliper a while ago

     

    All was fine when new then after a while it squealed, new pads, good clean and all was fine, bike sat for 3 weeks went to use it and brake squealed again

     

    Luckily it was under warranty, sent it back to chain reaction, they couldnt find a leak so they sent it back to shimano who pressure tested it and found one piston was leaking under pressure

    March 17, 2017 at 7:27 am #888999
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    bauchlebastart
    stub wrote:
    Hi bauchlebastart,

    I’m beginning to think that is the cause. Did a replacement caliper cure your problems? I’m just wondering if I’m doing something wrong to cause it…

     

    On both occasions, yes. Calipers replaced and the issue went away.

    March 16, 2017 at 8:09 pm #888997
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    CXR94Di2

    It’s the resin pads, when
    It’s the resin pads, when they get wet they deposit lots of material on the rotors. Clean the rotors with alcohol or brake cleaner thoroughly. This should eliminate the noise. It will come back when the pads get wet again. Upgrade to sintered pads, these are much better against squeal noises

    March 16, 2017 at 5:12 pm #888995
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    HalfWheeler
    bauchlebastart wrote:
    Leaking piston seals?

    This. 

    Had a smiliar problem with my Kona Cinder Cone. Went through umpteen calipers (mostly on warranty) before I figured out what was happening. This may not be the case with you but it was where I was storing the bike that was the problem. I have an Asgard metal bike shed, freezing cold in winter, boiling hot (like a parked car) in summer. Over the course of the year the seals would expand, contract, etc etc. The seals couldn’t take it. Fluid would leak onto the pads. Result; screeeeeech!

    March 16, 2017 at 4:12 pm #888993
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    part_robot

    Grease kicked up from the

    Grease kicked up from the road is usually the culprit. Bloody polluting cars!

    Remove pads and clean with Isopropyl alcohol (or replace). Remove rotors and do same. Hold discs with something heat proof, pour on alcohol and ignite. Do a few times. Let cool. Re assemble everything. Take bike to steep hill ideally without using brakes on the way there. Cycle fast down the hill and apply front brake to medium strength down to a jogging pace and then hard as you can. When you almost stop let go; do not let the wheels stop rotating. Keep going like this down the hill; fast-slow-fast-slow etc. Go to the top again if necessary and do again until you’ve  braked about 20 times. Discs will get really hot! Repeat with rear brake, with bum sitting over the rear tyre for extra traction. 

    Result; perfect silent braking in all conditions.

    March 16, 2017 at 3:52 pm #888991
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    stub

    Hi bauchlebastart,

    Hi bauchlebastart,

    I’m beginning to think that is the cause. Did a replacement caliper cure your problems? I’m just wondering if I’m doing something wrong to cause it…

    March 16, 2017 at 2:50 pm #888989
    0
    bauchlebastart

    Leaking piston seals?

    Leaking piston seals?

    Happens often with Shimano hydro calipers.

    Ive had this problem on two bikes, squealing rear brake, no power but no signs of leaks. Cleaned rear disc and replaced the pads, all was fine for a week then the problem returned. Had to replace the entire caliper as Shimano dont provide spares.

    March 16, 2017 at 1:08 pm #888987
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    Ogi

    Weird one. I don’t know,  try

    Weird one. I don’t know,  try cleaning the rotors with alcohol. If not, leave it for while for the pads to bed in and check it out if it keeps coming back later. It might help to take a steep descent and step on the brakes a bit, to maybe remove this top film/layer that seems to be the problem. I assume you’re talking of this extreme squeeling in dry weather, bcs in the wet –  this is expected to some degree with some pads.

    March 16, 2017 at 1:01 pm #888985
    0
    stub

    Hi,

    Hi,

    I’m using the stock Shimano XT/SLX resin pad (J04?). I figured it best to replace the originals (using the XT RT81 rotors too).

    I always bleed with the bleed blocks (wheel off, no pads fitted) to avoid contamination. Initially the bike was fine when I rode it for a couple of months in winter. I put it back in the garage, got it out yesterday, squeals terribly.

    No brake rub at all (I centered the caliper post-bleed last time and it had been fine) – it’s only if you apply the brakes.

    March 16, 2017 at 12:55 pm #888983
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    Ogi

    Hi,

    Hi,

    Do you mind me asking which pads did you use? They might be of low quality.

    Secondly, by any chance did the oil spill on the pads/rotors when you were bleeding? If so, there you go.

    Do you have any brake rub on the rotors?

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