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Got a Scott carbon gravel bike and have noticed some brake disc rub at the rear. Tried realigning the caliper (using spacer, resetting pistons etc) but the only way I can get it to stop catching is if I loosen off the caliper mounting bolts slightly.
Any idea why this is the fix? and should I be worried, as I’m pretty sure it’s not at the 5nm recommended spec (sram rival axs). Using new rotors.
Is it dragging or just rubbing slightly. It's fairly normal to get a slight bit of rub. IME, simplest way to deal with it is to find a big hill and drag the brake all the way down. If that doesn't fix it, check that the rotors aren't warped.
If it's actually dragging, check that the system isn't overfilled with fluid.
Also check the mounts don’t need facing.
I fitted new SRAM pads and rotors to my SRAM Rival brakes and I couldn’t even get the rotors between the pads without some force initially. Basically had to drag down a long hill to wear away some pad material. At which point I discovered uneven wear as the pads didn’t fully cover the rotor and I had lots of squealing noise so I needed to get the mounts faced.
The callipers definitely should not be loose enough to move when the levers are squeezed though…
Its just rubbing slightly and only on a certain part of the rotor. They are brand new rotors though so shouldn't be warped?
I had to manually position the caliper to stop the rubbing, its only when I tighten down the calipers to the frame (to torque spec) that the rubbing happens again, like it moves the caliper angle position when its torqued (just guessing though).
The calipers are not loose, but not as tight as recommended.
If it moves when you tighten it then you’ll need the mount facing is my guess, as that’s exactly the symptom. It’s exacerbated by new pads as there’s less tolerance until they wear down.
does it need a spacer to lift the caliper ? like a little 0.5mm washer for example.
They are brand new rotors though so shouldn’t be warped?
the 2 centre lock rotors on my gravel bike were bent from new, and have never been great at staying true. I'd just straighten it out
Its just rubbing slightly and only on a certain part of the rotor. They are brand new rotors though so shouldn’t be warped?
Rotors are never perfectly flat. Try centering the caliper then remove the wheel and gently push the pads apart so the pistons are retracted back into the caliper. Then refit the wheel and pump the lever to reset the pistons. If they still rub after doing that, you need to either straighten or replace the rotors (or just tolerate the rubbing).
Sometimes when you tighten the caliper bolts, the caliper can move slightly, I think the bolt heads drag it slightly.
Try nipping the bolts up very gently while holding the caliper with the rotor perfectly in the centre, then gently tightening each bolt.
Also, are the caliper pistons clean and moving evenly?
👆That’s a good idea too. I tighten mine just enough so that I can still move the calliper and then centre it by tapping with a small wooden handled screwdriver and then tighten each bolt a smidge at a time while holding the calliper in place .
Needs to be central over the disc then get the pads moving correctly.
See last minute of this vid-
Yeah I think the caliper pistons are fine/clean. It is pretty much a new bike.
I've done the gently tighten technique, I think i'm struggling to hold the calipers in place whilst I tighten to proper spec. Anyway, more tinkering required - thanks for all the help so-far