Problems with disc brakes on daughters bike

[5potTurbo]

Afternoon all!

I'm hoping someone can help me in my quest to solve an annoying problem with the disc brakes on my daughter's bike.

I bought a Raleigh MTB for her for Christmas 2010. In recent months I noticed the discs, when they're rotating, touch the pads, making an annoying squeaking sound when they do.

To avoid having to buy new discs, are these shims (only washers really?) perhaps the remedy so the discs spin in a more uniform manner, i.e. with less lateral movement, enabling me to centre within the pads more effectively?

http://www.halfords.com/webapp/wcs/stores/servlet/...

If this would be the remedy, should I actually bother with the shims, as they're packaged, and simply try some washers instead?

Sorry if this is a silly question, but I've really no experience with disc brakes on bikes!

Thanks in advance!

[Beyond Rational]

These washers are not for lateral movement in the discs but rather the positioning of the caliper relative to the disc and the brake mount. If you have warped or bent rotors, you need to replace them or bend them back.

For safety's safe, I would suggest visiting a bike shop.

[Jimbo.]

What brakes?

[kamilb1998]

I would suggest checking trying to adjust the caliper mounting position. If this doesn't work try and see if it could possibly be a bent wheel from hitting a pothbole or something. It could also be a bent/warped disc which may need replacing.

Before I got the Sinclair I had a cheap MTB with disc brakes and they were constantly going wrong, finally a fitting a set of replacement discs and wheels I had lying around fixed the problem.

[Beyond Rational]

I should have added that you need to check the bolts holding the disc are tight.

[5potTurbo]

Thanks for all your responses.

I can categorically state the wheels are true and my daughter's a "proper girlie girl" when it come to going up/down pavements, etc. - getting on/off her bike!

The disc is also firm attached to the mounting points.

The shop I bought this Raleigh bike from (Auchan, Luxembourg) aren't interested in helping, so much for their "Service Apres Vente", and, sadly, other bike shops charge a whopping €40/hour. If they take too long to fix the problem it would be cheaper to replace the bike!

Jimbo. said:

What brakes?

The front disc brake! - unless you mean their make?
It's some obscure Chinese make, "Sunyung" or something, and when I checked the manufacturer's own website they don't list discs as a replacement part.

That said, assuming the disc has the standard fixing points and is of a standard size, it shouldn't be too difficult to change myself - should it?

[timbo48]

Two things. I imagine that the discs are a cable operated system rather than hydraulic. If so the cable might have stretched. You can adjust this at the lever end.
If it's not this, or they are hydraulic, use the shims (they should be various thicknesses) to get the disc as central as possible, hold the brake on by using the lever and then tighten the caliper bolts.
You don't make it clear as to whether it's a constant rubbing noise (adjustment should deal with this) or one that rubs say every revolution of the wheel. If it's the latter it's more likely to be a warped disc.
Could possibly be paint finish on the frame mounts in which case you may still be able to adjust them but getting these mounts faced at a LBS would be better.
It's a fiddly job and doesn't just happen on cheaper end 'bikes.

[5potTurbo]

Hi Timbo

Reading your post makes me think I wasn't very clear in my OP, so I'll try and make it as clear as I can.

It's "only" a £120 bike for my daughter who's 10, but the annoying squeak of the disc against the pads at a certain point in each revolution is very annoying - probably more so for me when I'm cycling alongside her than it is for her - but she's only 10!

The brakes are cable operated, (£120 bike) and I've checked and adjusted them, but the disc's seemingly warped. I can't imagine that was from a high speed very strong braking incident if you woudl see how fast (slowly!) my daughter can cycle! It's a sham though as the bike's not had a great deal of use since it was bought a year ago.

I think I'll go ahead and check the discs are a standard mounting and replace the front item.

Thanks again.

[JPJ]

If it is the disc that's bent slightly in one place, they can be straightened with long nose pliers and a bit of patience. Best done with the bike in a makeshift stand (hang saddle from rafter in garage roof perhaps) so you can spin the wheel and identify the point at which the noise is created, then tweak gently with the pliers until the noise goes away.

[CoolC]

Sounds like a job for a couple of adjustable spanners. Carefully identify where the warp is and then use small movements to bring the disc back into line.

As you say it's a £120 bike so I can't imagine the discs are of the higest strength hardened steel IYKWIM.

[deadtom]

do what JPJ and coolC have said.

if you try this and still no luck, then yes the rotor will probably be a standard size (probably 160mm, and it might even have it engraved on the rotor itself) and the mounting points on the wheel hub will (almost certainly) also be standard.

[5potTurbo]