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Well, it will shift to a higher gear, but it takes two clicks of the shifter and it skips over a gear when it does shift. With one click the chain hangs on the current gear by the slimmest if threads. It's quite amazing really.

This is a new derailleur, a Shimano RD-M410 Alivio SGS, on a cog set that predates index shifting. Could that be the problem?

I have tried adjusting the barrel adjuster, but that doesn't seem to have any effect (on this problem).

Also, I put bar-end shifters on the bike, so the cable seems a bit short.

Edit

The cog set has 7 gears, but the shifter has 8.

Thanks.

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What shifters are you using? And what cog set do you have? Predates index shifting? What else does it predate? I had an early 80's racing bike with indexed shifting. –  DC_CARR Mar 29 '11 at 18:07
    
I don't recall the model of the shifters. They are shimano, purchased recently, are for 8 speeds, and have a combo friction/index mode. I'm pretty sure the original derailleur is an Altus and non-indexed. I've read that these were pre-cursors to indexed shifters, but not quite there. The bike is a LeTour from 83-84. –  Steve Mar 29 '11 at 18:43
    
Try this: sheldonbrown.com/derailer-adjustment.html –  sillyyak Mar 29 '11 at 19:06
    
@sillyyak The article had a note about alternate cable routing to use when there are 7 cogs but the shifter has 8 positions - exactly my situation. I am also pretty sure the cable loop just before the derailleur is to short. I will check both tonight. Please put your comment as an answer so I can give you credit if that solves the problem. –  Steve Mar 29 '11 at 19:37
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can you put the note about using a 7-cog cassette with an 8-speed shifter into the body of your question? That's very important information! –  darkcanuck Mar 30 '11 at 3:22
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6 Answers

up vote 0 down vote accepted

I am not above easy points!!!

:)

sheldonbrown.com/derailer-adjustment.html

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I believe it was a combination of using the alternate cable routing and tweaking the barrel adjuster as several people suggested. However, it was the sheldon brown page that clearly pointed out what to do when having trouble going to a higher gear vs going to a lower gear. –  Steve Mar 30 '11 at 1:20
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Perhaps your shifter cable can't slide smoothly. Shift to the tallest gear (smallest cog). Pop the shifter housing out of the brazed-on stops. Slide the housing back and forth and look for stiffness. Put some lube in the housing and slide it back and forth to distribute it.

Perhaps your derailleur hanger is bent. A bike shop will have a tool to easily check its alignment.

If either of these is a factor, then you will never be able to adjust your shifting properly.

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neat tip on how to check the feel of the cable housing –  memnoch_proxy Nov 5 '11 at 3:44
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I suggest starting from scratch. First,shift onto the highest(smallest) cog and release the cable from the DR (derailleur). Hold the end of the cable and make sure it's moving positively each time you operate the shifter.

If that's the case, make sure you've moved the shifter back to it's highest-gear position and re-attach. Make sure there is no slack in the cable at this point... It should feel taut but not tight when pulled away from the frame. Now, cycle the shifter through it's travel; it should be very close at this point. If there is any hesitation in jumping from one cog to another, you should tighten the barrel adjuster just a quarter turn or so at a time till you get clean shifts. I'm going to assume at this point that being a new-ish bike, the stop screws on the DR do not need to be adjusted. Naturally, if the chain falls off either end of the cassette that's not the case... Oh, while you're down there, make sure the DR hanger (the little bit sticking from the frame that the DR screws into) is straight. Sometimes those replaceable aluminum hangers are very soft and bend easily.

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Does it solidly engage in the cogs on either end of that mis-shift? It sounds plainly to be like a mis-indexed cable. You should be able to shift into that 'barely-not-shifting' position and then loosen the barrel adjuster to cause it to index into place. If that's not happening, your barrel adjuster may have stripped threads.

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Yes, most gears are solid and quick. I don't know what a 'mis-indexed' cable is. –  Steve Mar 29 '11 at 18:36
    
I will double check tonight that the barrel adjustment does not fix this, however, I don't believe the threads are stripped as it's new. –  Steve Mar 29 '11 at 18:38
    
Try running through all of the gears with your shifters set to their friction setting instead of the index setting, also. That will tell us if the problem is in the indexing or if there is some issue with the cluster or with the cable. –  DC_CARR Mar 29 '11 at 19:33
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If you're using 8-speed bar end shifters with a 7-speed casette, I have an alternate solution for you. Many bar end shifters (for the rear derailleur only) can be switched from indexed mode to friction mode. That would allow you to shift smoothly without any peculiar cable routings.

If your shifter does this, it will have a screw (typically with a handle) just on the left side. Unscrew it a few turns and you will notice the shifter indexing gets "softer". After about 3-5 full turns the indexing should disappear completely and the lever action becomes smooth. Instant friction shifter! (should work with any number of rear cogs)

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How much clearance do you have between the top pulley on the derailleur and the cogs? It's unlikely to happen on all cogs, but if there's not enough clearance between cog and pulley you won't be able to shift down. You will usually hear the pulley running along the cassette when this happens. This is usually fixed by removing a link from your chain.

But the above answers are much more likely to fix your problem. Broadly, if there's too much friction in the cable the spring in the derailleur won't be powerful enough to shift properly. You can test for this by pulling the derailleur out while shifting, and if the extra force from your hand makes it shift then this is the issue. Fix it by putting lightweight lube in the cable (solvent-based chain lube works well), or installing new cable and housing.

Often this would also happen with a worn out derailleur, but since yours is new that's not the case.

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