Rear shifter stuck for 7/8

[irumman]

Hi all,

I am using Trek 3900 disc and am a newbie. I am facing a problem with my rear derailleur. It does not change when I try to move gear from 6-7/8. Otherwise working okay but not perfect. I tried to loosen up barrel adjuster but it got stuck and are not moving counter clockwise anymore.

Little bit history:
There were some noise when I was paddling and I found that the noise was from the rear derailleur. The chain was not going to the cassette cleanly from lower pulley and this was the reason for making noise. I moved the high and low limit screw a bit and then I found that the problem was removed, but then I got the problem that the gear shifter was not working even from 1-2. I moved the barrel adjuster again and again but it was not working. Then I removed the back wheel and installed again and then the shifter started to work for 1-6, but not for 7/8. And again there were noise when the chain is was going from lower pulley to cassette.

Guys, as I am newbie I might make some mistakes with the names of the parts. If yes, pardon for that and let me know so that I could make you the experts understand my problem.

Please provide me some advice what to do now.

 

[oldbobcat]

You need to first determine whether the problem is caused by the shifter, the derailleur, or the cable that connects them. This topic has been discussed in countless threads that can be searched. Also, the Park Tool company has an excellent online tutorial on setting up rear derailleurs. See http://www.parktool.com/blog/repair-help/categories/derailleur-systems, especially the sections on Shifters, Rear Derailleur Adjustments, and Rear Derailleur Alignment.

 

[tafi]

Originally Posted by irumman .

Hi all,

I am using Trek 3900 disc and am a newbie. I am facing a problem with my rear derailleur. It does not change when I try to move gear from 6-7/8. Otherwise working okay but not perfect. I tried to loosen up barrel adjuster but it got stuck and are not moving counter clockwise anymore.

Undoing the barrel adjuster (turning anti-clockwise, as you say you have done) tightens the cable. In order to get changes to smaller sprockets (from 6 to 7 and to 8) you need the cable to be slacker (ie screw the barrel adjuster clockwise). You may have added too much tension or you may also have screwed the barrel adjuster out completely.

Limit screws do not assist with gear changing (except into the largest and smallest sprockets) and once set, they should be left well alone.

The procedure for setting or tuning the rear derailleur is generally:

1) Ensure the hanger and derailleur are straight. Straigthening may require someone with experience and specialist tools.
2) With the cable detached, set the limit screws so that the derailleur will move the chain (when pushed by hand) into the lowest (biggest sprocket) gear and (when pulled by the return spring) into the highest (smallest sprocket) gear. These limits should also be set to prevent the chain being thrown off either side of the cassette (but particularly into the spokes). After this, leave the limit screws alone!
3) Attach the cable, clamp it and tension appropriately so that gear changes are accurate.

Hope this helps you. But if not, don't be a fraid to take it to a bike mechanic who may even show you how it is done.