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I ran into an unfortunate situation earlier this week. I was out on a mountain bike trail, alone — just me and my hardtail. I'm pedaling, when I suddenly hear a CRUNCH and my bike stops. The hanger has broken, and the derailleur is totally bent.

picture of broken derailleur

I couldn't pedal, because the derailleur would travel with the chain and get stuck in the gears, and I had no way of reattaching it.

Luckily, I happened to be pretty close to the town when this happened, so I ended up walking it for ~15 minutes and dropping it off at my local bike shop.

However, I'm wondering what I can do if this happens again and I'm at a less convenient location - say deep in the woods. I don't generally carry any tools besides for a Swiss Army knife and an Allen wrench set.

Is there anything I can do to patch it up enough to at least get back home if I happen to break my derailleur?

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    See also my question on rear derailleur breakages (also a duplicate of the one I linked above, but with some useful material of its own) – Chris H Jan 24 at 8:02
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    And definitely upgrade your tool kit to include the means to deal with a broken chain, which will also allow you to shorten your chain to an emergency single speed. While you're at it, make sure you're set up to deal with punctures (even if you run tubeless). – Chris H Jan 24 at 8:04
  • Possible duplicate of Rear derailleur breakages – David Richerby Jan 24 at 10:07
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    Wow. In 35 years of fairly frequent bike riding with derailleur gear shifts I have never even heard of this. There is not much mechanical load on the arm, is there? What do you think caused this? In any case I think there is a plethora of more common incidents to prepare for (among others, I've had about three broken frames in this time period) -- I'd not bother with this fluke incident. – Peter A. Schneider Jan 24 at 14:32
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If you carry a multi-tool which happens to include a chain tool, you could also convert your bike to a single speed. If you do so, you would have to replace the chain afterwards as well (since you shorten it) but in some situations it could get you out of a rural area.

If you do so, carefully select the gear you would put it in, as you won't be able to shift anymore afterwards.

There is a nice video online illustrating the idea: how to do a roadside fix of a broken rear derailleur. GCN has some more videos online explaining roadside repairs of various issues, which may also interest you.

Additionally, I always take a missing link with me, as it allows you to get home after a broken chain. This speed link can also be used while converting your bike to a single speed.

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    I'll add a couple of points, having had this happen to me: 1 - if you have a chain with a missing link on your bike, it's REALLY hard to open a missing link without either the proper tool or a pair of pliers 2 - after you shorten your chain, it's still going to move around on the cassette and "self-shift". You have to be really, really careful that your chain doesn't "climb" the cassette far enough and under enough stress to snap the chain or break something else. So you'll need to be going slow and careful. I found that leaning the bike could coax the chain one way or the other a bit. – Andrew Henle Jan 24 at 11:17
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    It’s really hard to properly tension the chain without horizontal dropouts or a chain tensioner. I guess loosening the chain ring, “shifting“ to a larger cog and then tightening the ring could help. – Michael Jan 24 at 12:36
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    @AndrewHenle: you're right that it's hard to open a missing link without the proper tool. Point 2 is indeed also a valid one, it's not a perfect solution but might help you to get back home... If I would have a chain tool with me, I would break the regular links and use the spare missing link to fix the shorter chain. That way you never have to open a missing link on the road. Ps: if you can't get the the missing link "locked", move the chain so it's in the upper section and put some stress on the chain by pushing the pedal ;-). – cookiemonster Jan 24 at 14:37
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Another suggestion: Scooter it.

The bike is functional but the drive train cannot transmit power.

So one solution is to scooter along with one foot on the opposite pedal, and your other foot pushing directly on the ground. This can be uncomfortable, so rotating your saddle ~30 degrees to the opposite side from where you're standing can give your hip something to lean on.

You can still use your brakes to slow and stop,and steering is just like normal.

This suggestion is pretty useless if there are any uphills, or any challenging terrain to cross.

If the chain is slapping around, you can tie it to the chainstay with cableties/slipties, or if your equipment loadout is missing these then long grass or flax or even soft twigs can help retain things.

If your chain has a master link, then dropping the derailleur and chain completely off the bike and into a plastic bag can help too.


Related answer Tow it out

If you are riding with someone else then see if they are prepared to tow you out. All the above applies, but you'll be moving faster so secure any loose bits.

The towstrap needs to be long enough that the tow-bike's back wheel clears the towed bike's front wheel. Half-wheeling can bring you both down if it all goes poorly.

A spare innertube or two makes an adequate towstrap. A suitable branch might work but will require some creative mounting to the tow-bike. Fasten the towstrap to the front bike, and the disabled bike is NOT secured - instead the back rider holds the towstrap in their secondary hand and steers/brakes wiht their primary hand.

Communication is critical, and not going too fast. If anything goes wrong, the towed rider simply drops the strap and steers/brakes with two hands. There is no need to tow on a downhill. Do take the easiest line everywhere - remember the tow-bike rider is doing a lot more work than normal, so you will owe them.

Aside - those loose bits can help with repair later on, so don't litter/lose them. If not refitted in the repair, then they can help identify the right replacement hanger to buy.

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    Walk up, scoot down or on the flat, carry over serious terrain. A map may help - here in the UK most of the trail centres are criss-crossed by fire roads which can provide a short easy route out - if they go the right way. – Chris H Jan 24 at 8:06
  • I once broke a cup on the side of my bottom bracket, and lost all the bearings on that side. I reasoned that scootering 5 km was okay because the BB axle was fine with no bearing surfaces touching anything, and the cup needed replacement anyway. – Criggie Jan 24 at 10:43
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I hope that your derailleur hanger was a separate part and not integral to the frame.

Some options:

  • If you do have a separate derailleur hanger you can carry a spare. If the hanger gets broken install the spare. You will need more tools than a few hex wrenches to do that, maybe pliers to hold the broken hanger while you unscrew the derailleur bolt. Of course if you break the hanger you may break the derailleur as well.

  • Carry a chain tool and spare joining pin or quick link. If the hanger or derailleur breaks: remove it, shorten the chain and make a singlespeed with the chain on a chainring and sprocket you can pedal out on.

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    You also need to have some cable ties or electrical tape or some such to tie up the loose cable. – Daniel R Hicks Jan 24 at 0:12
  • @DanielRHicks an easy way to take up cable ends on the road is to clamp them off to a bottle-cage boss. Twice I've done this with most of my RD cable (admittedly to my tourer's 3rd cage under the downtube) after it snapped in the shifter. It's secure enough to hold it in gear, never mind to take up slack – Chris H Jan 24 at 16:39
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This is a last resort and is a dirty bodge. Not recommended.

Use your multitool to undo the lower jockey wheel from the rear derailleur. Mind out for small parts - keep them.

This would let the chain come free. You may choose to undo the inner cable from the derailleur and pocket it, or tie the derailleur up high on the seatstay out of the way.

At this point you have a massively long chain. Pressing a pedal will tension the top, and the lower loop will dangle, probably dragging on the ground. You can then set the chain on the middle or big chainring and gently ride.

Downsides:

  • At the rear the chain will probably migrate toward the smaller cogs. Every time you lean the bike, the dragging chain will want to step to a smaller cog/higher gear, so you have to keep the bike as vertical as possible.

  • You might ride over your own chain with the rear wheel.

  • You will damage your chain, possibly ruining it.

  • The chain will try and step off the smallest cog to the right, and could wedge between the frame and cassette.

  • There's an enormous risk of the chain catching something on the ground. This could stop you suddenly and promote the situation from a mere mechanical to a full-on injury situation.

Upside: You're rolling, not walking.

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