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Disc brake vibration & mega squeal

scooterbscooterb Posts: 76
edited July 2019 in MTB workshop & tech
I’m sure my pads aren’t contaminated ?
The front brake is fine & totally quiet but the rear Is horrendous and I can’t stop it from squealing sending vibrations through the frame ?

Its a carbon hardtail stumpy
Deore m615 Caliper with Shimano resin pads .
Hope 183mm rotor
I’ve thoroughly cleaned the disc rotor
Checked the pads which look ok , gave them a flat rub on sandpaper

What happens is - when Im coming to a near stop the rear brake starts to squeal sending mega vibrations through the rear carbon frame stays .
It’s ok when travelling at speed just when coming to a near stop as you ease off the Caliper .
I’ve tried using a smaller rotor - no difference
There’s no signs of any leaks and the pads look ok
I’ve swapped the front and rear pads

Anyone got any other ideas I could try ?
https://photos.app.goo.gl/uipoh866F3C1zgHw7
https://photos.app.goo.gl/Urydi6H7LKbfMSWf8
https://photos.app.goo.gl/fX4B5EjpCJjdYXej9
https://photos.app.goo.gl/ksU5Tixahb1MAkuN6

Posts

  • robertpbrobertpb Posts: 1,866
    Misalignment?
    Now where's that "Get Out of Crash Free Card"
  • scooterbscooterb Posts: 76
    All true and straight ,
    just been reading that the rotor can get scored so I wonder if that’s the cause ?
    it does have some wear on it , when you run your nail over it you can feel the lines but not that deep .
    I guess the only option is buy a new disc and pads .

    I’ve also read about bedding in the disc and pads when new so will follow that guide .

    What a ball ache ! The rotor seems to have loads of life left as do the pads .

    More money to throw at it :evil:
  • JBAJBA Posts: 2,707
    I’d say misaligned caliper as well.
    Align the caliper by eye. Use the ‘seam’ on the caliper as a datum and line it up with the disc and torque the bolts.
    Then remove the wheel and use a pad spacer or suitable flat item to spread the pads and fully retract the pistons. Refit the wheel and pump the brake to reset the pads.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Bird Zero Mk1 ¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • scooterbscooterb Posts: 76
    Yeah ok , I’ll give that a go too.
    Cheers
  • steve_sordysteve_sordy Posts: 2,126
    I had what sounds to be the same thing. Coming down the mountain you could hear my car horn blare all over the valley!

    I went through EVERY SINGLE IDEA THAT ANYONE EVER HAD and nothing worked. I swapped a complete brake set and that worked, but I wanted to fix it. In the end I dismantled the bike and sold the bits. But what I now believe it to be was a very small amount of air in the hose that acted as an air spring. This allowed the vibrations from the pad/disc interchange to bounce (vibrate).

    Put the brake full on hard and tie down the brake lever with a zip tie. Store the bike with the front wheel high so that the rear brake hose has nowhere that air can collect anywhere except in the lever assembly. Leave it overnight or longer, then do a front end bleed.

    Let me know how you get on, please. :)
  • scooterbscooterb Posts: 76
    Will try that too .

    How about I just bleed the brake again with new mineral oil which I have .
    I did notice that when I flip the frame upside down and back to upright the rear lever pulls in further than normal then after a few pumps goes back to normal , so I wonder what that would be .
    Worth a full bleed I reckon .
  • cobbacobba Posts: 282
    What size post mounts are on the frame?

    The adapter looks to be a 160-203mm/+43mm.

    When the wheel is on the frame, is the outer edge of the rotor near the outer of the braking material on the pads?
  • scooterbscooterb Posts: 76
    The adaptor is 20mm

    Not sure I can get it much closer , probably about 3mm before the Caliper hits the rotor
    Take a look
    https://photos.app.goo.gl/WajKi9H1eXX9mAiA8
    https://photos.app.goo.gl/YjR3GVzPTavqxdvi8
    https://photos.app.goo.gl/NhWrZe8xh5CtkJmt5
    https://photos.app.goo.gl/2e8vbntdtnHcc2Jv7
  • cobbacobba Posts: 282
    scooterb wrote:
    The adaptor is 20mm

    First photo shows a C stamped on the adapter, it's a Hope 160-203mm/+43mm adapter.

    If the frame has 140mm post mounts, the adapter would be the correct one needed.

    140 + 43 = 183

    If the frame has 160mm post mounts, it would be the wrong adapter.


    The last photos don't show anything other then the type of adapter that you have.

    Turn the bike up the correct way, look into the top of the caliper and see where the top of the pads are in relation to the top of the rotor.

    The braking material on the pads should not overhang the outer edge of the rotor.
  • scooterbscooterb Posts: 76
    Ok ,
    I’ve removed the pad spring to make it easier to see .
    It looks pretty flush , maybe 1 mm overhang ?
    What do ya think ?
    https://photos.app.goo.gl/h2H4nESWA4AtLLnWA
  • cobbacobba Posts: 282
    Should be ok, if you get a lip developing on the pads sand it down.

    At first I thought you had the wrong adapter, not a lot of bikes have 140mm post mounts.
  • scooterbscooterb Posts: 76
    Ok thanks ,
    And I guess this is normal that the pad has a slight bit of play on the width inside the Caliper ,
    You can see the small gap on right side of the pad back plate .
    It rattles around a bit when inside the Caliper , could be triggering the vibes ?
    https://photos.app.goo.gl/nvfWMaqkRb6APcEn8
  • cobbacobba Posts: 282
    scooterb wrote:
    Ok thanks ,
    And I guess this is normal that the pad has a slight bit of play on the width inside the Caliper ,
    You can see the small gap on right side of the pad back plate .
    https://photos.app.goo.gl/nvfWMaqkRb6APcEn8

    Yes, that's normal.
  • JBAJBA Posts: 2,707
    Another thing to try is dome washers under the bolt heads. Adapters can sometimes cause the calliper to lean slightly so the pads don't sit parallel to the rotor.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Bird Zero Mk1 ¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • cobbacobba Posts: 282
    JBA wrote:
    Another thing to try is dome washers under the bolt heads.

    They aren't needed with the adapter that's been used.
    Adapters can sometimes cause the calliper to lean slightly so the pads don't sit parallel to the rotor.

    The only time you'd use those washers between the caliper and the bolt head is when the top of the caliper isn't parallel with the underside of the bolt head.

    This image shows where you'd use them:
    https://ep1.pinkbike.org/p4pb15830280/p4pb15830280.jpg

    Tech doc: https://si.shimano.com/#/en/SI/8170A
  • JBAJBA Posts: 2,707
    It's worth a try though.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Bird Zero Mk1 ¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • cobbacobba Posts: 282
    JBA wrote:
    It's worth a try though.

    Waste of time and money.

    Those washers won't change the pad alignment when placed between the bolt head and the caliper.
  • keef66keef66 Posts: 13,123
    But what I now believe it to be was a very small amount of air in the hose that acted as an air spring. This allowed the vibrations from the pad/disc interchange to bounce (vibrate).

    Ooh, wonder if that's what's going on with my wife's car? It's had new discs, pads and calipers, and I bedded in the new pads properly according to Brembo's instructions, but there's a persistent barely perceptible vibration / pulsing through the brake pedal that's not going away with continued use. Think I'll get the eezibleed out at the weekend and push through a bit more fluid to see if any tiny bubbles come with it...
  • scooterbscooterb Posts: 76
    I’ve thoroughly bled mine now , made no difference ☹️
  • billycoolbillycool Posts: 833
    We've all had different experiences and various solutions to similar issues in the past, so it's hard to know for sure.

    Personally, I'd try new pads and discs. Remove the chance of any contamination.
    Check everything that should be bolted tight is done correctly (I'm sure this has been done already)
    Check alignment etc best you can (there have been some comments about adaptor mounts etc)

    Would a cracked frame/seat stay cause vibration and/or misaligment of brakes?
    "Ride, crash, replace"
  • scooterbscooterb Posts: 76
    Yeah , that’s my next option , new pads and disc .
    I’ll take a good look for any cracks aswell , Hope not :(
  • robertpbrobertpb Posts: 1,866
    When all else fails put some copperslip on the end of the pistons.
    Now where's that "Get Out of Crash Free Card"
  • scooterbscooterb Posts: 76
    Yeah , not a bad shout .
    I was thinking it could be the pads which triggers it , rattling .
  • take the pads out and inspect the backing plate for any minute traces of oil
  • steve_sordysteve_sordy Posts: 2,126
    Try Swissstop disc brake silencer.

    http://www.swissstop.ch/silencer/

    But the small aerosol, its all you need to test it and use it more than a few times. No point buying the big one if it won't fix the problem for you.

    Remove the pads and spray a quick blast (very quick) onto the pads. Best to do one at a time. The pads will go black! Refit the pads and go for a ride on the street to bed them in. Be prepared for the brakes not to work at all despite repeated application on hard stops. Then all of a sudden they start to bite and then one more application of the brakes and you will be standing the bike on its nose (if you were testing the front brakes).
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