HELP! Disc rotor moves independently of hub?

[arallsopp]

Howdo.

Mrs' new bike has arrived in a big cardboard box, flat packed. Fair on, its a folding bike, so no worries there. Have put pedals on, mounted the handlebars (levers were already attached), hooked the front brake cable into the lever, and put the saddle post in. All looking decidedly bike like.

Bike is a Dahon Cadenza 8, and a lovely one it is too.

Only problem I'm having with the assembly is re the front brake. Standing astride the bike with the front brake on, the front end exhibits a slight rocking that made me think the headset was loose. Having had a closer look, its the disc brake rotor. Whilst the rotor stays absolutely clamped by the pads, its still possible to rotate the wheel about 1.5 degrees clockwise / anticlockwise. This says to me "that rotor isn't clamped properly".

Anyone have any idea where to start?

 

[Steve Austin]

Have you checked the rotor bolts are tight?
If they are it could be the pads rocking a bit in the caliper, they sometimes do this. Or it could be the caliper that isn't tightened enough to the forks.

 

[arallsopp]

Thanks Steve,

I'm pretty sure the rotors aren't rocking in the caliper, nor caliper on fork, as I can stand the bike up, tyre touching tarmac, pinch the rotor twixt finger and thumb, and still turn the rotor back and forth whilst the wheel sits still.

Must be the rotor bolts.

mMMMmmm... They look good. Infact, the movement looks to be between the whatever the rotor bolts are attached to, and the hub itself. I'm looking at this: http://techdocs.shimano.com/media/t...eSystem/SI_8E80A_En_v1_m56577569830604346.pdf and thinking its something to do with the rotor installation ring, or tightening plate. Plate seems to move with the rotor, if that helps?

 

[Mr Pig]

Is it a centre lock rotor?

Is the rotor itself held to the 'spider' part with rivets or bolts? If it's rivets it's a centre lock rotor.

 

[arallsopp]

"Rivets" said Andy, scratching his head...

 

[Mr Pig]

Ok, that's a centre lock rotor. It's held on with a lock ring very similar to the ring that holds the gears/cassette on. In fact it's the same tool for both. What you want to do is look and see if the ring is loose. If it is you'll have to remove the wheel and tighten it up.

It can only be tightened with the right tool, the correct torque is marked on the ring but it is 40Nm, which is 350 in lbs in old money.

 

[arallsopp]

Cheers Mr Pig. I'm guessing 'the right tool' probably isn't a hammer or a hacksaw. Darn. That's my toolkit exhausted.

...off to the bikeshop goes the bike

 

[Mr Pig]

Cheers Mr Pig. I'm guessing 'the right tool' probably isn't a hammer or a hacksaw.

It's the same tool as the cassette lock ring. They come in most bike tool kits, a good investment.

 

[spandex]

Cheers Mr Pig. I'm guessing 'the right tool' probably isn't a hammer or a hacksaw. Darn. That's my toolkit exhausted.

...off to the bikeshop goes the bike

Thats the best thing to do as if you get the brakes wrong thats it

 

[Mr Pig]

Thats the best thing to do as if you get the brakes wrong thats it

Actually, the point of the centre lock rotor is that it 'can't' go wrong! Even if it is loose it is still splined to the wheel and will still work. It'll just float around a bit. Not a bad idea.

 

[Monst]

Ring Dahon?! Its a new bike, thus they can advise properly.

 

[jhkuo]

Just want to add that the Dahon cadenza 8 (2008 model) I bought in Oct 2009 also had the exact issue. I ended up taken it back to the shop to have the rotor tightened.

 

[arallsopp]

If it reassures, having tightened things, its been good ever since.