I have a crack on my front derailleur braze on on my carbon bike.  The crack is narrow and is not all the way through the braze on tab - on inspection it does not appear to be deep.  Unlike most bikes, the braze on is actually moulded as part of the frame and not riveted or bolted on - so a replacement is not an easy option.

I was considering repair options, and wondered if using your Black Epoxy Repair filler would suffice or of there was a better recommendation?

The tab holds the front derailleur onto the bike - so the stress of the derailleur moving the chain between chain rings is all it has to deal with.  It is an electronic shifter, so there aren't any additional forces from a cable that a mechanical shifter would cause.

Thanks
Steve

Can you post some pictures of the damage? It sounds like some filler is all you need, but it could possibly be more extensive than that. 

A crack means it has failed all the way through the piece. Posting pictures would be the place to start.
Fred

A picture would be essential so we can see how best to carry out a repair, if possible.

Although with bike repairs we generally we don’t want to encourage people tomake repairs to structural and safety critical part like a bike frame withoutexplaining that any work undertaken would be at your own risk, any advise givenis given in good faith and no guarantees or assurances can be made as towhether a repair is appropriate or safe to do. If in any doubt, either replacethe frame or take it to a professional.

With that said, if you do wish to undertake arepair yourself then it’s often perfectly safe and easy to make a good repairand restore strength to the frame. If the damage has broken or split the carbonfibres themselves (i.e. it is structural damage) then you can add new layers ofcarbon fibre to the part to return the original strength and prevent furtherdamage.

 If you do make a repair like this then you shouldbe aware that you will always be able to see where the repair has been made.You can restore the strength in this way but not the original appearance. Tomake a structural repair to a bike frame I would recommend our Fishing Pole Repair Kit. Although it wasdeveloped to repair fishing poles, repairing a bike frame is done in exactlythe same way.

 The more fabric (and resin) that you add (i.e.the more times you wrap the fabric around) then the more strength you will addbut it the same time the repair will look bigger. The Fishing Pole Repair Kituses a very special, lightweight 90gsm cloth which allows very thin andlightweight repairs to be undertaken however if the damage is significant andyou intend to add 1mm+ or wall thickness by way of the repair then you shouldconsider additionally purchasing a small Carbon Fibre 2/2 Twill 3k 195g - Mini Roll 0.3sqm.This cloth is more than twice the weight of the cloth included in the FishingPole Repair Kit and would be ideal for larger repairs to heavier damagealthough if the repair is small you will be fine with just the 90gsm clothincluded in the Fishing Pole Repair Kit.

If you can post the pictures then I can give more precise advise than the generic advise above.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

While I am not the OP, I found this forum searching for an answer for the exact same situation, enough so that I registered just to add to this thread since it appears OP figured something out. I have included a picture of my damage. I have no experience with carbon repair or any material repair for that matter. I have seen a few walk through vids but I am hoping to just be okay filling the 'crack'(not sure if its much more than a surface fracture) and just eliminate the use of the front derailleur entirely which would put no more direct force to that area. If filler is acceptable, are there any carbon fiber fillers that dry white(ish)? Any help in this matter is greatly appreciated. 

Cracks in carbon are often like iceburgs - the bulk of the damage is hidden.

Using a filler won't repair the broken fibres and thus won't restore the strength.  You ideally need to add extra reinforcement to add strength back to where it has been lost.

It's a critical area of the frame so you need to be sure you have done the repair properly.  Might be worth speaking to a bike repair shop for thier views if you are in any doubts. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant