A broken rear derailleur my not mean an end to the ride. Removing the derailleur and splitting the chain so you run a single gear at the rear as a great ‘get you home’ trailside repair skill to know.
Disconnect the rear derailleur from the bike. If the rear derailleur is a mechanical derailleur, this will involve loosening the cable clamp with a 5mm Allen key so that the cable can be removed from the derailleur. The derailleur can then be removed from the hanger using a 6mm Allen key.
If the derailleur is electronic, it will involve unplugging the cable from the derailleur and removing the derailleur from the hanger by a 6mm Allen key.
With the rear derailleur disconnected from the bicycle but hanging down on the chain, wrap the gear cable neatly around the frame. If the gears are electronic, push the electronic cable back into the frame in order to prevent them getting caught.
To completely remove the rear derailleur from the bike, the chain must be split to allow the chain to be removed from the derailleur. To do this use a chain link extractor tool to remove a pin and split the chain.
If the rear derailleur is okay and it is the rear derailleur hanger that has broken keep the derailleur as it can be used again.
With the rear derailleur removed the only option is to now cut the chain to a length where it can only be used in one gear. Cutting the chain to this length will allow you to cycle home, so ensure that the gear picked is suitable for the terrain on your route home.
After selecting which gear to use to ride home, make sure that the tension of the chain is okay by pulling the two ends of the chain together and roughly lining up the end links. It is possible that in a certain gear the chain is too slack, in this situation select another gear which will allow for better tension on the chain when it is joined.
With the chain pulled together in the chosen gear, mark the link that needs to be split in order for the chain to be the correct length.
When splitting the chain, always split the chain to leave an open link with the pin still connected on one end and a closed link on the other end. This is done by using a chain link extractor to push the pin out towards the end of the link, but not all the way out of the link. As the link is being pushed out, the resistance of pushing the pin will increase, at that point stop as this means the link is within the outside plate of the link.
With the chain split to the correct length, loop the chain over the chosen gears and push the open and closed ends of the chain together. There should be enough of the pin protruding on the inside of the chain plate on the open link, that the pin should hold the closed end in place.
Using the chain link extractor tool again, push the pin through the centre of the closed end link and through into the other side plate of the open end link. This completes the join of the two ends of the chain.
The joining link could be very stiff, to loosen the link bend the chain side to side to free it off.
The chain is now connected and you would be able to cycle home. However, it has to be remembered that the chain will not be the perfect tension so there is a risk that it may fall out of the selected gear. This could be dangerous so take care and slowly cycle home.
Alternatively, there is another way of connecting a chain. Quick links can be bought which will connect two closed ends of a chain together. This method is much quicker and simpler. We would recommend always carrying a quick link in your saddle bag.
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This repair has been carried out on a component from a popular brand. If you are using a different component please refer to the manufacturers manual to ensure specific details of the component/task are known. The principles and general skills of the task can be transferred but maybe not the exact details.