Bicycle Mechanics - Rear Derailleur Arm Doesn't Hang
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05-25-11, 07:48 AM
I removed the bike chain and wheels to clean them but when I put it all back together I noticed the rear derailler arm isn't as vertical as before. It's actually so horizontal that the chain rubs against itself when using the smallest cog.
It seems like the chain is too long because if I pull it toward the front derailleur the rear arm goes into it's natural position. Problem is, I didn't change the chain. I checked and double checked how the chain is threaded through the derailleur and can't imagine it working any way other than how I have it.
It also didn't shift right going to the smallest cog when I rode it but if I flip the bike over and shift all the gears it works fine.
05-25-11, 09:06 AM
Sounds like you have bent the rear deraillur hanger when the wheel was off the frame. If you have bent the hanger, it depends on what the frame is made of / if the hanger is replaceable.
If the hanger is replaceable, then just replace it; normally Aluminum frames.
If it is non-replaceable, normally on Steel or Titanium frames, take it to your LBS, should be a cheap repair, the tool (Park DAG-2) is not normally worth buying for the home mechanic as it is so infrequently used.
Picture needed. If you never removed the dr/sounds like either the chain is threaded wrong or the cage got flipped (which amounts to the same thing. I've done this before (call it a brain fart). If the dr was removed/make sure it's oriented on the hanger stop. I take pics for ref now before I pull things apart :)
05-25-11, 09:32 AM
Thanks for the feedback. This is the best picture I have right now. I can take a better one when I get home if this isn't good enough.
How does the cage get flipped? Are you saying it spun around on the hanger?
05-25-11, 09:36 AM
This is the same model derailleur in the correct position.
When in the small chainring and smallest cog the derailleur shoudl be almost horizontal. However, you should avoid using the small chainring/small cog combination as this is cross chaining and causes problems. However, the chain shouldn't actually be rubbing on itself as it passes through the derailleur...
Did you remove the derailleur as well as the chain? If you did, it is possible you re-instaled the derailleur incorrectly - so that the b-tension screw (on the back of the derailleur body) is not pushing against the tab on the derailleur hanger.
If you are worried that your chain is too long, shift intot he large chainring/large cog and see how your derailleur sits: the derailleur cage shoudl be angled significantly forward. THis is generally the gear in which chain length is selected - find the length of the chain that goes tightly around the large chainring and large cog, then add two links.. this usually allows you to shift into this gear without jamming or ripping off the derailleur, but is not so long that things rub.
If everything is properly assembled, you could simply tighten the b-tension screw a couple of turns and see if that helps.
05-25-11, 10:14 AM
We need a picture of the deraillieur in the position that it is in now. from you 2nd post, sounds like it may nto be a bent hanger, has the cable come out of it's guide, do you just need to put it in the correct gear?
05-25-11, 10:25 AM
I didn't remove the derailleur. I tried adjusting the B-tension screw and it didn't seem to help. I'm pretty sure it was in contact with the tab but I will double check and take better pics tonight when I get home.
The cable didn't come out of the guide.
05-25-11, 10:29 AM
Well, then if you're not in the small to small combo then you somehow threaded the chain through the derailleur wrongly. Your picture doesn't show the whole chain path through the cage and jocky pulleys so it's impossible to say what is going on. But for starters with the rear still on that same sprocket shift the crankset up to the big ring if it's not there already. If the cage is still way back like this then see if you can pull it down and take a picture of it that has the cage angled the same as your other picture of the red bike.
I'm tipping there's absolutely nothing wrong and the OP's just got it in small/small.
+1 Small, small, which is a cross chaining no-no.
05-26-11, 07:47 AM
The chain rubbing did occur in small/small. It won't shift to the small cog at all now though doesn't matter which chain ring I'm on. I will post pics in a sec.
Hmm, any chance the cable housing is kinked or not properly seated or something?
05-26-11, 10:23 AM
05-26-11, 10:25 AM
05-26-11, 10:29 AM
Does the cassette look too far away from the wheel in the last pic?
What, exactly is the chain rubbing on? From you initial description it sounded like the chain as it enters the lower jockey wheel is rubbing on the upper jockey wheel. From the latest pictures, this rubbing is not occuring, so if there is still rubbing, it is coming from somewhere else.
And, looking closely at the first pic you posted, there is some clearance between the chain and upper jockey wheel there, too.
05-26-11, 12:20 PM
@DCBO, the picture was to illustrate how the chain is threaded so I put it on the middle chain ring so the arm would extend. Your description of the problem is accurate, beside that the bike wont shift to the smallest cog. It looks to me like the cassette could be half an inch closer to the spokes and the shifting issue would go away. Not sure how close they normally are though.
Cassette should not be able to move side to side on the cassette body. And if a wheel or hub places the cassette body a mm or two closer or farther from the wheel, this can be compensated for by adjusting the derailleur.
I think, if you are just having shifting difficulties, you should go to the Park Tool web page and follow their front & rear derailleur set up instructions to the letter, step-by-step without leaving anything out.
Some videos to watch
05-27-11, 09:26 AM
So I was able to get the bike to shift to the small cog again. The chain still rubs in small/small but I won't worry about it since I shouldn't use that combination anyway. Thanks for everyone's help. Now on to wheel truing...
Did you remove and rescrew the freewheel back on? It does look way too far away from the backside of the hub-happens if cross threaded. If the chain wasn't rubbing before/it shouldn't now. ????
05-27-11, 12:24 PM
Juls there was too much tension in the cable to let the derailluer move to the smallest cog. I didn't mess with the wheel.
05-27-11, 12:52 PM
If the only thing you changed was the limit screws to allow the dérailleur to be shifted to the smallest rear cog and it never was there before this repair, then your chain is too long and was before but you were not aware since it could not be made to rub like it is now. Check this out and see for sure: http://www.parktool.com/blog/repair-help/chain-length-sizing
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