Motorcycle front disc brake scraping sound

Question

Had my tyres changed on my CBF 125, last week. Since then, I've had issues with braking. I took the bike back to them and taking the wheel off (to change the tyre as it was already going flat) and putting it back on seemed to fix the weird brake feeling I had.

However, I've noticed that the front wheel, when spun on the center stand, makes a scraping sound. It's not loud, almost like two bits of metal sliding against each other. I imagine the brake pad is scraping. I've searched this and I've found people saying it's normal and others saying it's not.

What do you think? When I got home after a 25 mile ride today, the brake disc was particularly hot. So hot, I could barely hold my finger on it. The guy in the shop said that the brake pads were wearing low, so I'll be buying new ones next week. Not sure if the scraping sound could be because of this?

Answer 1

Assuming that disc brakes on a motorcycle are similar to those on a bicycle, it is possible that the rotor – which is on the wheel – is no longer aligned with the caliper on the fork. This could explain your first point if the wheel was not returned to its previous location after changing the tyre. All it would take for this to happen is for there to be a little bit of play in the fork where the axle is clamped. It could also happen if the axle was not quite tight enough and the braking forces have caused the wheel to shift a bit.

Some disc brake designs do not actively withdraw the pads, so a tiny bit of noise from dragging after applying the brakes might be normal, but a large build up of heat is not. That's energy being dissipated which wastes fuel and the heat can also reduce the effectiveness of your brakes.

Replacing worn pads is a good idea, but none of this sounds like it would be due to worn pads. I think there is an alignment issue between the rotor and the caliper/pads. If the front wheel is properly mounted and properly torqued, then it is possible that the caliper needs to be aligned (on bicycles there are a couple of bolts that hold the caliper on disc brake systems and, roughly speaking, you loosen the bolts, apply the brakes to force the caliper into alignment with the rotor, and then tighten the bolts – it's an easy process.

The other possibility is a warped rotor, but that is something that wouldn't be likely to be related to the recent work.