# When do you replace a rear derailleur?



## hardwarz (Jun 12, 2009)

Since it's winter, I decided to help my friend out and run new cables. Everything went fine, but his rear derailleur doesn't go from the larger cogs to the smaller cogs evenly. I had to replace his plastic derailleur guides, but now I think the spring that controls the return of the derailleur is weak and that the whole derailleur needs replaced. His bike is older so he has a Shimano STX rear derailleur on it.

Am I making the correct assumption to replace the derailleur?

Also, the front derailleur doesn't lock into the large chain ring. I believe it's a broken shifter that won't shift to 3. 1 and 2 work fine. What is the best way to test this?

Hardwarz


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## mik_git (Feb 4, 2004)

did it work before?

front, maybe cable stretch? can you physically move the derailleur with your hand?


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## hardwarz (Jun 12, 2009)

Did it work before? He was having problems. It's a 1999 with original everything.

Front derailleur I can move it with my hand.


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## AndrwSwitch (Nov 8, 2007)

"plastic derailleur guides" - jockey wheels?

To me, a rear derailleur is toast if you can wiggle the lower part, below the pantograph (the thing with the two parallel bars and most of the joints) mechanism, without feeling resistance from the spring. If there's play, get a new one.

Also, drip some Tri-Flow or something into all the pivots. If it's really dirty and sticky, it'll have a harder time with the shift you describe. If with clean, lubricated pivots the derailleur still won't move well, you probably need a new one.

Front derailleur sounds like it could be a limit screw problem. If it is, loosening the "high" limit screw (on top of the derailleur mount, with a little 'H' by it. They can be on either side, so look for the letters) will solve it. It could also be a worn out shifter, or you might not have taken the shifter to its lowest gear when you installed the cable.

Can you shift down again when you're in what you set up to be the lowest gear? If so, you had it in '2', not in '1' when you ran the cable. I never do that, of course. 

If the cable isn't attached to the derailleur, so there's no resistance, can you shift into '3?'

If the problem is the shifter, try flushing it with Tri-Flow or WD-40 and see if you bring it back to life. WD-40 should be followed by Tri-Flow or light oil after it dries. Shifters sometimes get jammed with grit.

And if all else fails, LX stuff is not _that_ expensive.


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## hardwarz (Jun 12, 2009)

"plastic derailleur guides" - jockey wheels **** Yes

To me, a rear derailleur is toast if you can wiggle the lower part, below the pantograph (the thing with the two parallel bars and most of the joints) mechanism, without feeling resistance from the spring. If there's play, get a new one. **** There is no play.

Also, drip some Tri-Flow or something into all the pivots. If it's really dirty and sticky, it'll have a harder time with the shift you describe. If with clean, lubricated pivots the derailleur still won't move well, you probably need a new one. **** The rear derailleur is covered in a sticky grease/oil. Maybe it just needs a good cleaning of degreaser and then relubed.


Front derailleur sounds like it could be a limit screw problem. If it is, loosening the "high" limit screw (on top of the derailleur mount, with a little 'H' by it. They can be on either side, so look for the letters) will solve it. It could also be a worn out shifter, or you might not have taken the shifter to its lowest gear when you installed the cable. **** Problem isn't a limit screw I moved it and set the limits by using my hand to push it.

Can you shift down again when you're in what you set up to be the lowest gear? If so, you had it in '2', not in '1' when you ran the cable. I never do that, of course. **** It goes fine between 1 and 2 and 2 to 1.

If the cable isn't attached to the derailleur, so there's no resistance, can you shift into '3?' **** I need to test this tonight.

If the problem is the shifter, try flushing it with Tri-Flow or WD-40 and see if you bring it back to life. WD-40 should be followed by Tri-Flow or light oil after it dries. Shifters sometimes get jammed with grit. **** The shifter that is having problems is missing the bottom dust cover, so there grit and grime may be in there already.

And if all else fails, LX stuff is not that expensive. **** Yeah, I found some new, pulls at Performance for $35.00 for a Shimano rear derailleur.


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## AndrwSwitch (Nov 8, 2007)

If you can get that front shifter working again, see if you can ghetto up a new dust cover. It's pretty important on bikes ridden off-road. Let us know how you do with cleaning and lubing - sounds like that may take care of both problems. Good luck!


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## jeffscott (May 10, 2006)

hardwarz said:


> Since it's winter, I decided to help my friend out and run new cables. Everything went fine, but his rear derailleur doesn't go from the larger cogs to the smaller cogs evenly. I had to replace his plastic derailleur guides, but now I think the spring that controls the return of the derailleur is weak and that the whole derailleur needs replaced. His bike is older so he has a Shimano STX rear derailleur on it.
> 
> Am I making the correct assumption to replace the derailleur?
> 
> ...


If it wiggles side to side it is toast....

If the spring is slack screw in the B screw....you can also take the thing apart and clean and grease the coil spring.

FD take the cable off and move the FD by hand up and down..(have you adjusted the high and low limit screws??? if so and if it moves okay then it must be the shifter or the cables..


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## ae111black (Dec 27, 2008)

when it looks like this


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## One Pivot (Nov 20, 2009)

i dont know your financial situation.. id go ahead and replace the shifters and derailleurs. could probably grab a cheap/reliable set off ebay for nearly nothing. 

ive seen deore rear d's for 10 bucks.


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## insanitylevel9 (Sep 23, 2009)

when it commits suicide like ae111blacks x9. that thread lasted way to long


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