The joys of carbon...

dermur · 31-10-2012 12:40pm #1

I was centering the rear brake (single pivot) on the bike the other day. While I was tightening the centre bolt back on to the seat stay bridge, the recessed cylinder nut started to peep out the other side of the bridge even though the brake was still a little loose. Not at all happy.

Not enough space for a torque wrench so I was using a regular hex key with thumb and middle finger applying force. Not even enough space to look through the bridge to check for damage since the seat post is in the way.

I suspect the wider top end of the cylinder nut has come too far through the carbon (frame and fork is carbon). I can take a look at the front brake to get an idea of what the recess might look like but in the meantime, anyone got any ideas for a fix?

I don't think putting a washer in would help much since the wide end of the cylinder nut is already a snug fit.
I could try putting tape around the narrow end of the cylinder nut to "wedge" it in place.
Worst case - get the carbon repaired (assuming [a] it's damaged and it can be repaired).

Any other ideas? Thanks in advance!

letape · 31-10-2012 2:53pm

Is it just that the brake nut is too long. These are available in different length for the front brake as forks are different thicknesses. It may be that yoiu are using a nut that is more suited to a front brake and therefore longer than you need.

Hungrycol · 31-10-2012 3:14pm

+1 on letape suggestion.

Besides, are these contact points not made of alu as I would imagine there's a lot of stress at this point?

dermur · 31-10-2012 9:19pm

Just had a good look around inside the housing with a torch & mirror. Thankfully, doesn't appear to be any damage to the bridge. Didn't have enough light to see if there was any alluminium in there though. Makes sense that there might be something to reinforce the carbon.

Anyway, fair play to letape, I think you called it - the only conclusion I could draw is that the cylinder nut is a little on the long side. At one point, I thought that maybe the front and rear nuts are different sizes and I had mixed them up but they're both the same length.

So I'll either try to get my hand on a shorter cylinder nut or maybe put a washer on the brake side to act as a spacer. Main thing is: no damage to the frame. *phew*

Bad form by Ridley though - would have expected their components to be a better fit! Especially for single pivot brakes that don't center as well as their dual pivot counterparts.

letape · 31-10-2012 9:38pm

Dermur - most brake sets include a washer on the inside anyway; although the washer is serrated to help hold the brake centred when the bolt is tightened. Should be able to pick one up or a shorter bolt at a local bike shop or on chainreactioncycles.

dermur · 31-10-2012 11:08pm

Yeah...when the either nut is inserted it protrudes by about 2mm. There's a serated washer on the outside alright (between the brake and frame) but doesn't fit around the nut. So when everything is tightened up, the washer will be pushing against the protruding nut (see below) rather than flush against the frame.

I'd be willing to bet money on it being the wrong cylinder nut that was originally used. The shop will hopefully have a shorter version for me.

On further inspection, Hungrycol is also right in saying that there are aluminium contacts inside the housing. So, I'm a little more confident tightening everything up without screwing up the frame!

Thanks for your help.

The joys of carbon...

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