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I took my bike for the first ride of the season yesterday and unfortunately it was pretty short. As I was cycling through the rear gears I hear a plinking sound and then a large clunk. I stopped immediately and went to inspect the back wheel where I saw the following carnage:

  • The plastic shroud that holds the return spring for the lower pivot was broken and the spring had been ejected.

Broken derailleur

  • The pulley cage was crushed

Crushed pulley cage

  • Two spokes were damaged, one snapped at the base of the rim (nipple?) and another snapped off at the hub.

Broken spokes

I suspect that happened where is the L limit screw was dialed in too far and the pulley cage was hitting on the spokes (thus the plinking sound) but when a spoke mounted reflector passed by it put enough force on the derailleur to break the shroud and mess up the pulley cage as well.

With the why and how aside I'm looking to repair the damage so I can go on cycling!

I'm fairly new to bicycle maintenance so I'm trying to understand this piece by piece. I obviously need a new derailleur, probably a higher quality one this time around. Is there anything a beginner should be aware of when buying a new one? Besides the minimum and maximum tooth sizes.

Secondly, is it possible to buy just a few replacement spokes (I've been mostly looking on Amazon Canada)? Should I replace all the spokes at the same time?

Thank you!

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    FYI the specs on your derailleur are at bike.shimano.com/en-EU/product/component/tourney-a070/… Its a 7 speed Tourney with a max tooth count of 28 (though it can likely do 30~32 and perhaps even more) Min count is 11 tooth. It is pretty much bottom entry grade, and would be hard to distinguish from a banana by function or feel. (still beats walking though)
    – Criggie ♦
    May 1, 2020 at 3:40

3 Answers 3

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I recommend you take the bike to a bike shop and let them deal with this.

  • Yes, you can get individual spokes, but they need to be exactly the right length, which is determined by the specific hub and rim you've got, and the lacing pattern.
  • You probably do not need to rebuild the wheel with all-new spokes, but if you do, it will probably be cheaper to buy a readymade wheel.
  • Lacing spokes and truing wheels is not exactly a black art, but it is an art about which entire books have been written. You'd also need a freewheel-removal tool to get at the drive-side hub flange.
  • I'm a bit concerned that the spoke nipples damaged the rim at the spoke holes where they pulled through. And it is possible that there are other problems that only an experienced eye will be able to spot.
  • It's possible the derailleur hanger is bent.
  • Your new derailleur will need to be compatible with your shifters and your freewheel. I'm guessing that will limit you to a Shimano Tourney.
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  • Thanks Adam, I was kinda worried this would be the case. Just one clarification, the spokes didn't pull through the rim, they just snapped at the base.
    – Duck of Death
    May 1, 2020 at 20:54
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Having done something similar myself last year, beware of damage to other spokes. I didn't break any at the time, but 2 snapped within 3km of each other, 150km later, and when I removed the cassette I could see that all the drive side outer spokes has chunks or of them. This was presumably where the chain ended up after smashing the plastic disc.

A new rear derailleur was needed as well as replacing all 9 damaged spokes. I replaced them one at a time, keeping the wheel dished and fairly true, so only a little truing was needed. This was before I ever built a wheel.

Getting something caught in the derailleur could have caused this. I think mine was due to a stick, I've heard of a crisp packet getting stuck in the cage and causing the same damage.

You also need to check the derailleur hanger isn't bent, if you fix the bike.

Another repair option if you like the bike is to buy a similar cheap second hand one (which doesn't have to fit you, but the components have to be compatible) and take parts off it.

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    Its amazing how little it takes to write off a rear mech. I dropped a couple of dog-poop bags out of my rear pocket, they caught on the lower run of chain, and got swept into the mech This jammed it up good, breaking metal and requiiring a complete replacement.
    – Criggie ♦
    May 1, 2020 at 12:43
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    @Criggie I guess when the chain jams in there you might as well be stamping on it with one end fixed and the other unsupported. Quite an effective way to bend metal
    – Chris H
    May 1, 2020 at 15:02
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Sure you can replace spokes yourself. You will need the correct spokes and a spoke key that fits your nipples. You also need a way to remove your freewheel.

However a rim that permits the spoke nipple to pull through the metal sounds extremely sketchy. I would not ride that rim.

Your rear mech is stuffed. It will never work right again, so other than salvaging the lower parts of another derailleur, replacement is your best option.

I also see a freewheel not a cassette, so this is either a really old bike or a BSO. I'm leaning toward BSO because of the visible disk brake rotor.

UPSHOT Instead of pouring good money after bad, its time to look for a replacement bike. A decent used bike will probably cost about the same as a bike shop's total charge to fix that.

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    Thanks! I had to look up what BSO is and yes, it's definitely a Bike Shaped Object. I got this a few years ago when I was a student, just cheap transport but you get what you pay for. Just to clarify the spokes didn't pull though the hub, they sheared off the threaded cap(?) that is inside the rim.
    – Duck of Death
    May 1, 2020 at 20:57
  • @DuckofDeath Oh okay - that's not quite as bad, and yes I'd have a go at fixing the wheel. If you're feeling competent with tools, give it a go. The rear mech is toast, perhaps you might benefit from a donor bike, or get a similar-age used bike and combine.
    – Criggie ♦
    May 2, 2020 at 2:18

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