Disc brake problem

[PpPete]

One of the boys has a disc braked MTB (cable operated). Discs are something about which I nothing.

Just in the last few days rear wheel has started rubbing in only one place around the rotation - not much, just enough to stop the wheel turning freely when spun off the ground, but not enough to slow the little tyke down.

All the bolts are tight, so I'm thinking he's bent the disc very slightly (he's not exactly careful) Difficult to see any "wobble" but can't think of any other cause?

I'm thinking next step must be to remove the disk and check on a flat surface, then replace if I can't tweak it back to flat with an adjustable spanner?

Any other suggestions?

 

[chris-s]

First off, try simply removing and replacing the wheel ensuring it is fully located in the dropouts.

Chris

 

[Andy_R]

You don't need to take the disc off, simply look down into the caliper while wheel is spinning and check the gap between pad and disc. You'll more than likely be able to see the disc "wobble" slightly towards the pads and you should see where the disc is making contact with the pad. Once you've identified the area that's out of true, firm but gentle pressure with your thumbs will be enough to straighten it out.

 

[Moodyman]

Could well be a bent disc (rotor), but try these before embarking on the big mission:

1) Wheel not sitting properly in the dropout - most common fault and easiest fix. Disc brakes more susceptible to incorrect sitting the dropout.

2) One of your pads could be wearing at an angle. So centre the pads by loosening the two bolts, squeeze the brakes hard and keep them squeezed. Now re-tighten the bolts. When you un-squeeze the brakes, the pads will move away and allow the rotor to spin freely. A bit like installing caliper brake for the first time.

 

[PpPete]

Have checked wheel sitting correct in drop-outs, and pads wearing evenly. Can see the wobble in the disc now (looking at it from behind in good light, which I wasn't before).

Disc is definitely bent. Not been able to shift it with " firm but gentle pressure with thumbs".

Most replacement discs (160mm 6 bolt) seem to be around £20.... which seems like a lot.
Anyone any experience with these Promax ones?
Thinking that if I get him mobile again with one of those I can spend a bit more time trying to get the OEM one flat.

 

[Moodyman]

Those ProMax look very similar to my Deore ones.

Worth a punt for that sort of money.

 

[Andrew_P]

Are they BB5 Disc brakes?

 

[MacB]

Disc is definitely bent. Not been able to shift it with " firm but gentle pressure with thumbs".

There's a chance you're being a bit hesitant, it needs a bit more than you might think. I bought one of the truing tools but a large wrench tightened down would work as well.

I'm guessing, not got to this point yet, that once you've retrued 3/4 times over a rotor lifetime then that would be about the limit. The great bit is that the only alternative is a new rotor, so you might as well give the existing one a proper go.

 

[Cubist]

Have checked wheel sitting correct in drop-outs, and pads wearing evenly. Can see the wobble in the disc now (looking at it from behind in good light, which I wasn't before).

Disc is definitely bent. Not been able to shift it with " firm but gentle pressure with thumbs".

Most replacement discs (160mm 6 bolt) seem to be around £20.... which seems like a lot.
Anyone any experience with these Promax ones?
Thinking that if I get him mobile again with one of those I can spend a bit more time trying to get the OEM one flat.

Heed MacB, for he is wise.

 

[PpPete]

Are they BB5 Disc brakes?

Nothing so fancy ! No recognizable name on them

Heed MacB, for he is wise.

I may just take the knackered disc to his Alladin's cave of wonders next time I'm passing that way.

 

[MacB]

Nothing so fancy ! No recognizable name on them

I may just take the knackered disc to his Alladin's cave of wonders next time I'm passing that way.

always welcome Pete, you have my number and know the way here now

 

[threebikesmcginty]

Heed MacB, for he is wise.

A wise guy!

 

[Cubist]

You're not in the "post a lie" thread now 3bm!

 

[Globalti]

Flinkin' blip! What a fuss about nothing! This is a routine matter with new discs.

Just get a wrench set slightly wider than the disc, pad with cloth and bend away using the centre seam on the caliper for reference. Go carefully and you'll soon have it bent straight.

*wander off shaking head in wonderment*