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  1. #1
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    Rear disc brake squealing when braking Shimano M395

    Good day!

    I would be very grateful if someone could advise me on a big problem with my new bike.

    Recently bought a Scott Aspect 620 with Shimano M395 brakes.

    I tried the bike in the shop and immediately noticed that the rear brake squealed heavily when used. Sounds almost like a car horn.

    Being a noob, I asked about it and was told that this was "normal" and should go away when brakes are broken in. I believed them.

    After about 200 km, the problem persisted and got worse, until at some point, there the lever had gone very spongy and the rear brake was virtually inoperable. There was also oil residue around the brake area.

    I took it back to the shop, where quite a disinterested looking mechanic looked at it and just bled the brakes. He then told me that the brakes were contaminated and he heated the pads to clean them, but didn't know what the problem was.

    While the brakes still sort of work, they squal as they did before. Again, there is buildup of oily residue around the brake, some 80 km later.

    The front brake worked fine and silent since day one.

    What should I do?
    Last edited by tlass; 07-17-14 at 09:53 AM.

  2. #2
    Nigel nfmisso's Avatar
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    return the bike, demand a full refund, then find a different bike shop.
    Nigel
    Mechanical Design Engineer

  3. #3
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    Sounds like you have a hydraulic leak, and the oil is contaminating the pads. I don't know the shop, but you're right that the mechanic was certainly disinterested. Simply bleeding the brake won't solve the cause, it only treats (temporarily) the symptom. It's equivalent to putting air in a flat tire without patching the leak.

    Go back, talk to the manager, and have him assign a new and caring mechanic (if he has one), and have the entire brake and line connection until he finds and addresses the leak. The likeliest cause is a poor line connection at the brake, but it could also be a faulty caliper.

    BTW- a leaky caliper can happen to anyone, and yes new brakes sometimes squeal a while before settling in. So far so good, stuff happens. In fact, this was an opportunity for the store to show that they stand behind their products. Instead, when you walked in with a very obviously leaking brake you got blown off as an inconvenience. Unless you sense a very positive attitude from the manager or owner, I wouldn't spend another nickel in that store.
    FB
    Chain-L site

    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  4. #4
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    Many thanks for the replies so far! I will take the bike to the shop tomorrow and ensure this time that the people there pay attention to the problem.

    When I took off the rear wheel, I put a plastic piece between the brake pads and started pumping on the lever. I then saw that the part of the piston that came out of its socket slightly was oily around the edges.

    Could it be that the seals are bust?

  5. #5
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    Quote Originally Posted by tlass View Post

    Could it be that the seals are bust?
    Sounds like that. Some calipers are rebuildable, some aren't. But on a new bike, and especially after the prior (dis) service I think you'd be entirely within your rights to insist on a new caliper. If they don't have it in stock, they should pull it from a new bike, and get you on the road forthwith. And buy you a beer by way of apologizing.
    FB
    Chain-L site

    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

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