Bicycle Mechanics - Can't shift to smallest rear cog
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05-22-11, 10:04 AM
This is on a 1984 Nishiki International. (Downtube friction shifters.) I haven't changed any part of the drivetrain, and I would be surprised if the previous owner did.
The limiter bolts are not the cause. I don't think it's the wire tension either. The problem was present both before and after having my derailer hanger straightened.
Could the spring in the RD have weakened over the years?
05-22-11, 10:38 AM
Only two things limit rear derailleur outward travel: the limit screw and cable tension. You can eliminate cable tension by removing the cable from the derailleur. If the derailleur still won't shift into the smallest cog, then it's probably the limit screw.
You can run a further check by sighting the plane of the rear derailleur cage in relation to the small cog. If the derailleur cage plane is outward from the smallest cog and still won't shift into the cog (or completely off the cluster), then there may be some debris in the cogs that prevents the chain from falling in. If the derailleur cage plane is inward from the smallest cog, then it's the limit screw or some debris in the derailleur that prevents its full outward extension. I assume we have ruled out a broken spring.
N.B. it's difficult to tell much from your photo. You're in a large cog but have not stated the lever's position. Give us a further hint by showing a full view of the rear derailleur. That will tell us the make and model. We may be able to find a link to its adjustment on the web.
05-22-11, 11:22 AM
Turns out, it's just me not thinking things through. I've fiddled with both cable tension and limit screw now, and it all worked out.
Whenever I've been adjusting the tension before, the limiter must have been ill-adjusted, and vice versa.
Follow up: Should cable tension be as high/tense as possible while also allowing smooth shifting, or is some slack justified?
05-22-11, 11:31 AM
The cable tension should be set as high as possible . But not as high to be interfering with the derailluar in the highest (smallest ) cog .
05-22-11, 11:45 AM
Should cable tension be as high/tense as possible while also allowing smooth shifting, or is some slack justified?Cable tension does not matter all that much with friction shifters. If the cable is too tight, then you will not be able to shift into the smallest/smaller cogs. If the cable is too loose, then you will not be able to shift into the largest/larger cogs. The no tension limit screw is set without the cable being attached.
Having a slightly slack cable for the smallest cog is no great deal with a friction shifter. The chances are that you will shift one cog at a time. You will get the sense of how much to move the lever to make a shift. It's most unlikely that you will move the lever more than is necessary to make a shift. Also, if the cable is slack and you are adding tension in the shift, you will be able to feel when tension begins. You will go quickly through the no-tension zone.
I don't have stops on my friction levers; they did not fit over the spigot. I can put all the slack I want on the cables. It's never caused me to miss a shift.
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