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I have bought this bike one week ago from a friend of mine, and when I checked it, it was clear that the rear brake caliper cable was loose. I could see, under the frame, the steel wire bulging from the lack of tension.

So I thought it was a easy fix, just tension the cable again, adjust the rear caliper and everything works, right? Apparently, no.

After retensioning the cable and adjusting the caliper, with a few squeezes in the corresponding brake lever, the tension disappears and the cable becomes loose again. I don't think the problem is the caliper cable nut, as the cable does not seem to move there.

One symptom it has, is that the lever is much more hard to squeeze compared to the front caliper one. I think that is a problem with the cable/housing, because I have removed the rear caliper from the frame and it does not seem to be blocked or stuck in any way.

Do you think the solution is to replace the cable?

Besides these problems with the cable, I am a little bit concerned that the quick release mechanism of the rear caliper has some kind of issue. It feels very hard to move compared to the front one, and I am actually able to drive it further the locked position (past the two white dots aligned). I don't know if this may also explain the loss of cable tension.

FYI: caliper/levers are 2016 Shimano 105.

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    If you disconnect the brake cable from the brifter, does it operate freely?Are you sure the cable isn't slipping? Re-adjust it, color on one side of the cable at the caliper with a sharpie and see if it actually is slipping.
    – Batman
    Commented Sep 20, 2016 at 23:45
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    I suspect that the cable is rusted up and seizing.
    – Daniel R Hicks
    Commented Sep 21, 2016 at 1:26
  • Its a bike less than a year old? I'd be astonished if its rusted already. Are you sure of the bike's provenance? Is your friend a bit shifty? Something smells odd about this problem.
    – Criggie ♦
    Commented Sep 21, 2016 at 3:52
  • I will check the whole cable by removing the handlebar tape. The bike itself is a specialized Allez bought in november 2015. He recently (3 months ago) changed the group set to a Shimano 105 one. I have the receipts and everything. What may explain the problem is that it was him that installed the whole groupset. So far, I have checked the front/rear derailleurs and they were correctly installed. But I don't know about the cables.
    – gstorto
    Commented Sep 21, 2016 at 7:03
  • You can check the brifter without removing the tape, and if you don't have internal cable routing, you can try to operate the brake by hand.
    – Batman
    Commented Sep 21, 2016 at 19:57

2 Answers 2

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If you fasten the cable anchor with the quick release at its "tight" position and then it's able to slip into a "loose" position, that sounds like a likely culprit to me. I haven't encountered a misbehaving BR-5800 QR yet so I don't actually know what to tell you there, but I think either the silver part in front comes off and is covering a bolt head that holds the whole thing together, or the whole anchor assembly threads in and out of it. I would investigate that and get the issue you describe taken care of either way. You want those dots to have zero ability to come unaligned unintentionally.

Other possible causes of the cable slackening issue:

  • The cable is slipping from the anchor bolt.

  • You've got braided housing that's bursting through a ferrule, possibly the hidden one going into the brake lever. Or it could have been installed without a ferrule. (Coil housings don't need a ferrule here but braided/compressionless ones do.)

  • Someone installed a poorly fitting ferrule at the brake lever end and it's gradually getting wedged further in.

  • The cable is in the process of fraying apart somewhere.

  • There's a rubber cable doughnut or three caught in a housing stop getting gradually squished more and more.

  • The piece of housing going into the brake lever isn't long enough, and as you squeeze the brake, it's getting worked in further as it gets increasingly kinked where it leaves the tape.
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The problem was with the cable/housing. I would probably pinpoint the source as the housing which goes from the frame to the caliper.

I could probably have done a cheaper fix by replacing just the last cable housing, but I have replaced all the cable and all the housings of the rear brake.

It is working smoothly now.

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    thanks for reporting back, that greatly helps other people finding your question (and answer) in future.
    – Móż
    Commented Sep 25, 2016 at 21:35

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