Need help with my mountain bike rear gear selector please

ferry

Hi , I have dug out my old Peugeot Origin mountain bike from the back of the shed and it has a damaged Shimano rear gear selector ( derailleur)?
I know nothing about bikes - Are these generally hard to change and how would I go about selecting the correct parts to replace it please?

Thanks
F x

wongataa

They aren't hard to change.  To change one you will need suitable size hex keys/screwdrivers/spanners for the various fixings and a chain breaker tool to take the chain off.

If you want a replacement one you will need to source a new one that is compatible with the number of cogs on the rear wheel and your shift levers on the handlebar.

inspectorperez

Not hard to change if you know what you are doing. I do many jobs on my own bikes, but I wouldn't tackle this job. Do you not have a mobile bike mechanic in your area? Our local "Nextdoor" community website is very useful in locating such people so it might be worth joining up for your own area and simply placing a request online. The main man in my own area works within the Social Distancing rules and is extremely competent and inexpensive. He will also source any needed components.

alembicbassman

If the rear derailleur has been knocked it's likely bent the hanger it is screwed onto. On steel bikes you can usually bend this back into place, but on aluminium bikes it sometimes snaps off. Many aluminium bikes have replaceable mech hangers, but they're quite expensive for what they are £15 ish. Shimano rear derailleurs (7 Speed Tourney) Start at about £12. A new derailleur will only work if correctly aligned, which may require a visit to a bike repairer.
The video below gives you a good idea.
https://youtu.be/tXfvW0L3iLM

vitaweat

Google "Sheldon Brown".  The website is really old and clunky but it is an amazing resource for cycle maintenance.