I want to put a new Sram X7 instead of killed one, should I open the chain (if I have no chain lock) or it's better to open the derailleur?

  • 4
    Personal opinion - Much better to open the chain. It's easier, and that's how it's designed to be.
    – JohnP
    May 23 '13 at 17:59
  • Agreed. Opening the chain is infinitely easier than trying to open the derailleur. Especially if you have a master link, but even without one it's not hard.
    – sevargdcg
    May 23 '13 at 19:41
  • @JohnP that is the answer. You should post it as such.
    – jimchristie
    May 23 '13 at 21:31
  • @jimirings - done.
    – JohnP
    May 23 '13 at 21:35
  • 2
    Old derailers (20-30 years ago) were designed to be opened. New ones, not so much. May 23 '13 at 21:49

It's much better to open the chain. Derailleurs are not really designed to be opened repeatedly, and doing so inexpertly can potentially ruin the derailleur. Chains might have either a lock link or a master link of some kind, find that open the chain and then thread the chain through the derailleur. If the chain does not have one of these links, you will need a chain tool to split the chain. DIY grade ones are quite cheap and do the job well, but you will need to read up on how to use it properly.

Also consider that if the size of the derailleur arm is different, your chain may need either fewer links or more links to fit properly.

  • And, if your chain didn't come with one, buy one of these. chainreactioncycles.com/Models.aspx?ModelID=871
    – alex
    May 24 '13 at 1:53
  • Are you saying new derailleurs aren't designed to have jockey wheels replaced or their bearings greased? Because that would suck.
    – armb
    May 24 '13 at 10:36
  • @armb - No, I edited the answer slightly. However, removing a chain is basically just pushing out a pin. Here is a link showing derailleur maintenance and all the springs/parts involved: parktool.com/blog/repair-help/rear-derailleur-overhaul
    – JohnP
    May 24 '13 at 14:29
  • 1
    But most of that isn't relevant to just opening it enough to put a chain through. If you don't have a master link, some modern chains have pins designed for single use only. Once you've got the chain the right length, if he's replacing like for like, undoing the dérailleur is probably as easy as splitting the chain, especially if he doesn't have a suitable chain tool. We're not talking about opening it "repeatedly", just once to fit it. On the other hand, he'll need a new chain sooner or later, and then it will need adjusting to length.
    – armb
    May 27 '13 at 21:18

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