Bicycle Mechanics - can you swop a derailer without splitting chain

that the question folks, my shimano sis is bent across the bottom pin and wont swing back out to the bottom 2 cogs under the spring pressure. looks like the chian needs splitting to remove it or am i looking at this wrong?

No, to your question. The derailleur cage is a closed loop; only an opened chain can be fed through it.

You can remove/replace rear derailleurs without breaking the chain if you just remove one of the pulleys, and loosen the other one... A lot of front derailleurs can be removed, as well, depending on if the cage is riveted or screwed together...

No, to your question. The derailleur cage is a closed loop; only an opened chain can be fed through it.
That's not correct, you can replace a rear derailleur without breaking the chain.

From the old derailleur, remove the small bolt that holds the lower pulley in place and remove it. Then "sissor" the two halves of the cage apart which will allow you to remove the chain from the old derailleur and the derailleur from the frame.

Remove the same bolt and pulley from the new derailleur and, again, sissor the cage halves apart. Thread the chain over the top pulley and behind the locator tab. Then pivot the cage halves together and install the lower pulley and mount the derailleur on the frame. Snug up both the lower and upper pulley bolts. Done.

For what it's worth, I've done it by removing the pulley and it's much more of a PIA than just breaking the chain, at least in my opinion.

No, to your question. The derailleur cage is a closed loop; only an opened chain can be fed through it.

Incorrect.

Urbanknight is right though, you might as well just break the chain and have done with it.

For what it's worth, I've done it by removing the pulley and it's much more of a PIA than just breaking the chain, at least in my opinion.

+1

Much easier to break the chain IMO.

If you have a master link chain like SRAM or Wippermann, certainly break the chain. If your chain uses a specific pin like Shimano ($) or Campy ($$$), I prefer to replace the derailleur without separating the chain.

For what it's worth, I've done it by removing the pulley and it's much more of a PIA than just breaking the chain, at least in my opinion.
+1
Most chains have a quick link allowing you to break the chain without tools. If you have a chain that requires a special pin or other special propriety part this would be a good time to change it out for something more user friendly.

If you have a master link chain like SRAM or Wippermann, certainly break the chain. If your chain uses a specific pin like Shimano ($) or Campy ($$$), I prefer to replace the derailleur without separating the chain.

There must be some Scot in your genetic pool.... :D

Having a healthy dose of Scot background I'd do the same in the blink of an eye.

For what it's worth, I've done it by removing the pulley and it's much more of a PIA than just breaking the chain, at least in my opinion.

+1. I think the OP might (and that is a MAYBE):


Not have the tools
Not have the experience of breaking a chain


In either case, it is a skill worth learning. You can get a chain breaking tool at most hardware stores for around $3.00 for the basic cheap-o version (which will work perfectly well).

Give 'er a try. PM me if you need help.

There must be some Scot in your genetic pool.... :D

Having a healthy dose of Scot background I'd do the same in the blink of an eye.
Well, not by heritage but my mother was actually born in Glasgow and maybe some of it stayed with her and got transfered. :)

Shimano pins aren't too bad at about $1 but a new Campy Permalink is nearly $20!

OK, if you want to take your derailleur apart, then I guess that it would be possible to remove the chain without opening a link. But why? Breaking the chain is not that big a deal; you ought to know how to do it anyway, and while you are at it, put a missing link removable link in.

OK, if you want to take your derailleur apart, then I guess that it would be possible to remove the chain without opening a link. But why? Breaking the chain is not that big a deal; you ought to know how to do it anyway, and while you are at it, put a missing link removable link in.
I don't know why everyone thinks opening the derailleur is such a big deal. You take out ONE small bolt, the pulley slides out, you thread the chain through and put the pulley and bolt back it. It takes longer to describe than to do.

If you're overdue to clean/lube (sparingly) the RD pulleys, then go ahead and take the RD pulley disassembly route.

If you're overdue to clean/lube (sparingly) the RD pulleys, then go ahead and take the RD pulley disassembly route.
In the OP's case the old derailleur has been trashed and is being replaced with a new one.

I agree with HillRider. It's (usually) a cinch to split the RD cage. Just remember *exactly* how the chain threaded it, though. Draw a picture if you need to. When you put it back together with the springs relaxed it won't seem to make sense.

what i did last year for the chains on all my bikes (except the fixie, because pressure is a bit high on the chain, and i cant risk a break cause i run brakeless) is invest 4 bukcs in a kmc or sram or wippermann connector link. they work like a charm and make repairs and thorough cleanings and chain replacements a breeze. i know its not free, but its well worth the money. those replacement chain pins suck and ive had breakage problems with them- walking 14 miles back to my car on a hot day when my mtb's chains replacement pin broke was such a bummer.

I still don't understand why you wouldn't pop the chain apart. Is it to avoid buying a chain breaker? Cuz that's a pretty useful tool, even if the cheap ones are total crap. I mean, how long is it going to be until your chain is done, anyway?

You can with a Suntour Cyclone and Vx rear derailleurs, and probably others:

http://farm1.static.flickr.com/25/35285654_82d587e6a6.jpg?v=0