New bike - scraping noise from front disc brake

[ElCani]

Someone higher up the thread suggested using a cardboard spacer between the pad and piston. Don't do this. For one thing, it's a bodge on an essential system and, well, cardboard does not fare well in the rain.......

that suggestion was made for setting up purposes; mechanical disc calipers need a clearance vs the fixed pad and this is one way of setting it.

cheers

Yes, cardboard shims purely to aid set-up, not as an integral part of the braking system!

[bgnukem]

Assuming the caliper has only one moving pad, then using the manual adjuster on the static pad, screw it inwards a few turns, then re-set the caliper position as before by pulling the brake on, then releasing and re-tightening the caliper mounting bolts, then back off the adjustable pad a few turns to obtain clearance between the adjustable pad and the rotor. You might also need to use the cable adjuster to back off the other pad (reduce cable tension) to ensure clearance at that side.

If the brake still rubs and there's too much free travel at the brake lever before the brake activates then it suggests the rotor might be bent.

If so, it can be carefully bent back into line using a large adjustable spanner adjusted to grip the rotor and lever it gently inwards or outwards (i.e. towards / away from the frame).

[jk49]

After wheel removal, if I don't follow the procedure I am about to describe, I get disc rub, despite clearances being set up correctly. I think it is just a simple way of aligning the disc with the caliper, BB7's FYI.
I put the wheel into the dropouts and while the skewer is still untightened, just tie the front brake lever tightly on with a piece of string, velcro strap or whatever comes to hand, so it grips the disc firmly. Only then do I tighten the skewer. You could also slacken the caliper bolts after tightening the skewer and repeat the lever trick before retightening the bolts, but the first way is quick and easy. HTH.

[rmurphy195]

Assuming the caliper has only one moving pad, then using the manual adjuster on the static pad, screw it inwards a few turns, then re-set the caliper position as before by pulling the brake on, then releasing and re-tightening the caliper mounting bolts, then back off the adjustable pad a few turns to obtain clearance between the adjustable pad and the rotor. You might also need to use the cable adjuster to back off the other pad (reduce cable tension) to ensure clearance at that side.

If the brake still rubs and there's too much free travel at the brake lever before the brake activates then it suggests the rotor might be bent.

If so, it can be carefully bent back into line using a large adjustable spanner adjusted to grip the rotor and lever it gently inwards or outwards (i.e. towards / away from the frame).

If its a TRP Spyre, which has 2 moving pads, then each is adjustable individualy. Once you have the brakes set up - following the TRP video on Youtube, paying attention to the angle of the actuating arm and ensuring the cables are routed correctly on it (mine weren't), then with the bike off the groind spin the wheel and gradually adjust each pad in/out. For the outer pad this can be done while the wheel is spinning, for the inner pad you will need a long allen key and will need to stop the wheel to make each (tiny!) adjustment.

The video is https://www.youtube.com/watch?v=wPTK0yEUI5s, you can start about 2 minutes in!

With bit of patience you will soon get the knack whatever the type of brake. As things settle down you'll need to re-do the operation a couple of times.

[reohn2]

They're cable disc brakes on a Merida mountain bike. When I spin the wheel the rotor seems to spin in line, but the noise does seem to be for about half a rotation rather than constant.

What make and model of cable discs are they?
Failing that what year and model of Merida MTB is the bike?

[poorlittlefish]

Thanks, everyone. The brake sounds like the one in this video: https://www.youtube.com/watch?v=h2rsdPFcNFw so I'll take the bike out and give it a chance to bed in. If that doesn't do the trick then I'll give some of your suggestions a go.