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Backstory: I currently have a BH Ultralight RC road bike that I use to ride to work. About 6 weeks ago I took it to the bike shop because the pedal was slipping over the cassette when I took off, so they changed the rear cassette and the chain, and they did a few other things. It cost $220, but The bike was running very smoothly.

Then about a week the dropout (that's what they called it) literally snapped and the rear derailleur got stuck in the rim. I took it to the shop again, they straightened the "transmission" (what they said), they also straightened and reused the chain, they changed the spoke and they installed a dropout. I picked it up and took it home.

The issue is that I rode it yesterday for the first and the ride is terrible: the pedal's slipping again, the chain is always scraping something regardless of the shift, and it's making all kinds of noises. It's just terrible.

Since they said that the cassette and the chain was damaged from the dropout break, I'm almost sure that they'll want to change the rear cassette and the chain once again. My concern is that the dropout has never snapped like it did before (I didn't even know that existed), and I'm thinking that it broke because they didn't install something right the first time I took it.

Question: is it possible that the dropout broke because something wasn't done correctly when the new cassette was installed?

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  • I doubt the dropout itself broke as they're not generally replaceable parts, could you post a picture? I've looked online and can't find a closeup of that area Some designs have a derailleur hanger that follows the shape of the dropout; they can bend or break, and lead to derailleurs getting stuck in wheels (normally the spokes rather than the rim but it could end up anywhere). After similar damage a new chain was a must on my bike; the cassette was fine, but is probably a bit more robust than yours
    – Chris H
    Commented Nov 4, 2020 at 15:47
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    Do you actually mean the dropout or just the derailleur hanger? I assume you mean the chain is slipping over the cassette. Do you know why the derailleur hanger broke? What were you doing when it did? It could be that they made the chain too short or didn’t adjust the derailleur limits correctly but it could also be that you bent the hanger (causing the chain/derailleur to get caught in the spokes) or something got caught in the derailleur or chain. Your current problems sound like they wanted to do it as cheap as possible (instead of replacing everything) and didn’t do a good enough job.
    – Michael
    Commented Nov 4, 2020 at 15:48
  • I don't have a picture but I found a picture of the dropout. I've edited the question.
    – rbhat
    Commented Nov 4, 2020 at 15:54
  • The chain was slipping over the cassette, so they changed the cassette and chain in the first visit.
    – rbhat
    Commented Nov 4, 2020 at 15:54
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    The picture you've added clearly shows the hanger.
    – Carel
    Commented Nov 4, 2020 at 19:06

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It is possible that the rear derailleur low limit screw was misadjusted such that holding the shifter down allowed the RD to get snagged by a spoke. That is a fairly common cause of what happened.

Another possibility, also common, is the hanger (what you are calling the dropout) got bent inward for whatever reason, usually uncareful handling of the bike or crashing, after it left the shop, and the RD was able to get snagged that way

Unless something like a stick or vertebrate got caught in the wheel while riding and was able to reach over and snag the derailleur that way, it's likely one of those two scenarios. If you knew what click the shifter was on when it happened, that would be a clue.

It would be weird if the derailleur was unscathed enough to not need replacing completely. They're unobtainable for shops in a lot of cases right now, so that could be a factor that led to some kind of decision to de-mangle rather than replace it, which is idiotic in normal times but can now legitimately constitute good customer service. If this is what's happened, it could be causing the current bad performance and noises, as they usually wind up too misaligned and sloppy to work great. It's also of course possible they just did a bad job.

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  • Or the hanger got bent because somebody pushed/stepped/knocked into the rear end of the bike in some way. Check both rear triangles for scratchmarks or chippings.
    – Carel
    Commented Nov 4, 2020 at 19:04
  • I know of a case where the cause of an RD going into a wheel was a crisp packet; I believe mine was due to a stick. In my case it wrote off the RD, newish chain and 9 spokes. The derailleur was a twisted mess with a snapped cage plate, and the 5mm-thick steel hanger (part of the frame) noticeably bent.
    – Chris H
    Commented Nov 6, 2020 at 13:47

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