There is only one way to repair a carbon dropout and that is to replace the carbon with an injection molded part. Why? Carbon bikes are made approximately in 2 ways: Lay up for the tubes and injection moldings for the high pressure sections such as the dropouts, brake mounts, some front mech hangers. If these components are repaired in any other way they will most likely fail as the first picture shows – the 3rd attempt before sending it to us.
This blog is an edited extract from an email response I write almost on a daily basis for cyclists wanting an alloy insert fitted to remove the issue of wear. Since my earlier blog on the subject I have changed my opinion on the solution slightly – The problem many cyclist are having with excessive wear to the ‘face’ (Fig. A) of their carbon dropout is not only due to the carbon compound. Read on..
If there is wear to the skewer face, especially on the drive side, then it is probably already too late to simply to ‘rebuild’ the contact face. The slot itself is also worn in almost all directions (Fig. B). Misalignment of the wheel in the arch area should be your first clue.
This could be solved by sorting out the depth & width of the slot first. If you only build up the dropout face and clamp the wheel in, the drive side force on the wheel still causes movement within the distorted slot shape which is worn but the constant movement back & forth. This in-itself causes the dropout face to rub off whatever material to put on.
We used to put alloy faces on the dropouts (still can at more expense) but during A/B tests we found that if the slot shape was a tight(ish) fit and the customer clamped down the skewer sufficiently then there was no need for an alloy face. In fact if the above was not addressed this alloy face would also wear over a short time. On the whole carbon dropouts are rubbish as the record stands but sort out the dropout slot first and the dropout repair will hold well enough 🙂