I need to replace a Shimano Deore RD-M531 rear derailleur which has a long cage (9 speed cassette). I can replace the derailleur no problem, but my knowledge isn't great and am just not sure what to replace it with. This is an old bike and I would be happy with second hand to minimise costs. I would buy the same but none available on line. Any suggestions? Thanks Matt

  • That should read Shimano Deore RD-M531 Sep 2, 2015 at 8:43
  • Probably best to ask at your LBS (Local Bike Shop) rather than just ordering something over the internet... Sep 2, 2015 at 11:22

2 Answers 2


Shimano Deore RD-M591 is a comparable part which you can still find -- this is probably what I'd use. If you want to go a bit cheaper, Shimano Acera M360 will work too.

You can use any 7-9 speed Shimano rear derailleur to replace another 7-9 speed Shimano rear derailleur provided it has the appropriate capacity (*) for your setup (at least big chainring - small chainring + big cassette cog - small cassette cog) and largest cog rating, since the cable pull is the same. 10 speed onwards has a few more cases.

(*) Capacities tend to be conservative -- you can usually exceed them by a bit if you don't use absurd gear combinations.


I would recommend staying far away from used derailleurs, generally by the time they are taken off a bike, they do not function as they should. (bent hanger or cage, etc...)

Check ebay for good deals, When I searched this you could buy one for $23.50 shipped

  • I take your point. Looking at the used ones on ebay doesn't fill me with much hope. Thanks Sep 5, 2015 at 16:40

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