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Rear Derailleurs for Dummies(11 posts)

Rear Derailleurs for Dummies_sprocket_
Sep 6, 2002 6:16 AM
The cage on my rear derailleur comes way too close to(basically touching!) my spokes when I'm in the 39x25 (smallest gear). How can I adjust this? The bike shifts fine so I don't want to mess it up. Please be as specific as possible!
re: Rear Derailleurs for DummiesChen2
Sep 6, 2002 6:27 AM
This sounds more serious than a simple adjustment of the limit screw. Is it possible that you have a bent derailleur hanger, or a badly out of true wheel? I recommend that you take it to a reliable mechanic. Whatever it is, it can be fixed.
re: Rear Derailleurs for Dummiescharyne
Sep 6, 2002 6:29 AM
Not our of true wheel, but out of dish wheel!
re: true vs dishChen2
Sep 6, 2002 9:12 AM
You're right, but to me being "out of dish" is just another way of being out of true. When I true a wheel the rim will be centered.
Sep 6, 2002 6:30 AM
There are two screws on the side of the derailleur. The lower one, I think, determines how far inward the derailleur can go (if you get the wrong screw, just return it to where it was). Turn it in one turn and see what happens. Try to shift to the large cog. Keep turning in the screw until it won't shift to the large cog; after you reach that point, back off a little just until it is able to shift correctly.

Further information:

Chen2 is right about possible causes and taking it to a shop. However, you may want to check out this online maintenance guide as well:
Sep 6, 2002 6:31 AM
Wow, how did that happen?! Try this insteadTig
Sep 6, 2002 6:32 AM
Is it touching or not?TJeanloz
Sep 6, 2002 6:31 AM
If "basically touching" means that it is very, very close but not actually touching (ever, including when you sprint or climb); do nothing.

If "basically touching" means that it is actually touching, turn the left screw (upper limit screw) clockwise a VERY little bit (no more than 1/4 turn); double check your shifting.
Is it touching or not?_sprocket_
Sep 6, 2002 6:39 AM
It touches when I climb (I can hear it). I'm afraid the hanger might be bent from a little accident I had. :( Should I try to straighten it? I'm afraid I'm getting in over my head.
Is it touching or not?gtx
Sep 6, 2002 6:47 AM
if you think the hanger is bent take it to the LBS.
My bet is with Chen2.Spoke Wrench
Sep 7, 2002 4:36 AM
I'd say that the most likely causes are an inadequately dished rear wheel or a slightly bent derailleur hanger. Both are quite common.

Once a bicycle is set up correctly initially, there is seldom a need to "screw" with the derailleur limit adjustments. Most often that just creates additional problems for your bike mechanic to figure out.