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Help in adjusting my disc brake..

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  • October 2, 2019 at 7:08 pm #30165
    Huckfinn

    Hi all,

    I’m trying to work out how to fix the rear disc brake on my new (600km so far) Canyon Grail.  Nothing major but quite annoying and wouldn’t mind to learn to fix it myself!                            Basically :

    1- I noticed the back wheel does not spin as long as the front one when lifting the bike off the ground.

    2- When braking hard downhill it makes this light (but not that light) clunk..clunk..clunk kind of noise.

    3- Tonight I checked the rotor and noticed these regular “straight” kind of dark lines on the interior part of the rotor (picture shows only some of them but they’re regularly repeated in every section in between the fixing bolts).

    4- I also noticed that when braking with wheel off the ground, the wheel tends to move slightly inwards….

    It’s my first disc brakes bike and I would be grateful if someone suggested what to do.

     

    Thanks!

     

     

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  • October 2, 2019 at 9:32 pm #950643
    0
    Podc

    Rear wheels don’t spin as

    Rear wheels don’t spin as well as front wheels due to the extra drag from the freehub – in my experience anyway.

    October 2, 2019 at 9:08 pm #950641
    0
    hawkinspeter

    Re-adjusting the position of

    Re-adjusting the position of the caliper is an easy enough task and is worth knowing how to do.

    Loosen the two hex bolts that hold the caliper to the frame so that there’s some lateral movement of the caliper. Then there’s two methods that can be used:

    • Squeeze the brake lever so that the caliper will centre itself over the rotor and tighten up the caliper mounting bolts to keep it in place. (This is what the mechanic did)
    • Eyeball the gap between the rotor and the brake pads. A light background makes this easier, so hold some white paper the other side if it helps. Move the caliper so there’s the same gap either side of the rotor (usually it’s only about 1mm or so) and then tighten the caliper mounting bolts.

    I’ve found it can be tricky if when tightening the caliper bolts, it shifts the position of the caliper, so watch out for that happening. Once you’re happy with the position make sure you tighten the caliper bolts up to the recommended torque (from memory it’s probably around 5Nm).

    I prefer eyeballing the rotor as it also highlights any problems if the rotor is bent when you spin the wheel.

    Once the caliper is in the right place, it shouldn’t need re-adjusting often – maybe after replacing pads or a rotor but otherwise the thru-axle should keep everything firmly in place.

    October 2, 2019 at 8:41 pm #950639
    0
    Huckfinn

    Hi, and thanks!

    Hi, and thanks!

    I’ll check tomorrow morning on the potential side to side movement, but the reason why I think it’s only a matter of adjustment of the brake is because a few weeks ago I asked a veteran cyclist/mechanic why it would be that the back wheel wasn’t spinning much. He had a look and said: it’s the brake! So he unscrewed it from the frame, asked me to pull the brake lever, fidgeted with the caliper, retightened it to the frame and…voilà, everything was fine. 

    Unfortunately he doesn’t live nearby….

    October 2, 2019 at 8:10 pm #950637
    0
    hawkinspeter

    Maybe dodgy wheel bearings or

    Maybe dodgy wheel bearings or possibly the thru-axle isn’t correctly fitted. Can you feel any side to side wheel movement with your hands when the bike’s off the ground?

    The marks on the fins are curious as they shouldn’t be touching anything. Can you eyeball it when spinnng the wheel and see if there’s anything it could be hitting? Also, it’d be worth double checking that the rotor is good and tight.

    October 2, 2019 at 7:11 pm #950635
    0
    Huckfinn

    Got it. Here’s the photo.

    Here’s the photo.

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