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rear derailleur skipping specific gears

Old 07-30-12, 11:24 AM
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rear derailleur skipping specific gears

I am relatively new to biking and I'm still trying to learn to work on my own bike. I just picked up a older raleigh mountain bike from a friend. 2 weeks ago he had his lbs do a full tune up on it right before he sold it to me. It had only been used once since the tune up and it was a light trail.

Now I am noticing it is skipping specific gears when shifting. this is only happening on the rear derailleur. The rear derailleur is a shimano 300 lx and the shifters are the sti 200 gs. For the ease of explainging I am going to call the largest cog 1st and the smallest 7th. When starting in first it will shift perfectly all the way till 6th. when I shift to 6th the chain will skip for a minute then jump to 7th. when I am downshifting back to 1st it will stay in 6th with no issues but skip on 5th and jump to 4th and when shifting again skip 3rd completely and sometimes skip 2nd going straight to 1st.

This is only doing this on the smallest gear on the crankset, if I shift it up to the middle it will not do this. (at least not yet) I haven't tried the largest cog though.

I have looked over the cassette and there are no worn or broken teeth. The bike shop adjusted everything 2 weeks prior to this so I dont think it is out of adjustment although this is possible.

My question is does something sound broken/bent or does this sound like an adjustment issue and I should just try adjusting it myself?

Thanks for all help in advance
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Old 07-30-12, 11:35 AM
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You shouldn't use the smallest cog with the small chainring, nor should you use the largest cog with the largest chainring. This is called cross chaining and puts extra lateral stress on the chain- causing premature wear to the chain, cogs and chainrings. The skipping is probably a minor cable tension issue- it likely shifted fine on the work stand, and the shop didn't check their work with a road test.
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Old 07-30-12, 11:50 AM
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I went out and tried adjusting the cable tension and it made no change, Also I was wrong in my first post it is doing it on all three front cogs. I was on the middle cog and it was still jumping the same gears. I had the same outcome with the largest cog to. Is it possible for the indexing to get out of alignment or something like that?
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Old 07-30-12, 11:52 AM
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That sounds more like a stiff link in the chain or a bent derailleur hanger.
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Old 07-30-12, 11:58 AM
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Originally Posted by AADrcw
I went out and tried adjusting the cable tension and it made no change, Also I was wrong in my first post it is doing it on all three front cogs. I was on the middle cog and it was still jumping the same gears. I had the same outcome with the largest cog to. Is it possible for the indexing to get out of alignment or something like that?
My guess is you need to tweak the limit screws on the RD. I had a similar issue when I changed my cassette, everything worked fine but it was prone to jump when I was using the smaller sprockets. A twiddle with the limit screws fixed it.

I've still got an intermittent issue where the largest sprockets sometimes skip under heavy load, need to get it back on the stand to fix that. It's probably a related issue, maybe the cable has stretched a little since I last adjusted it.
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Old 07-30-12, 12:02 PM
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Limit screws have nothing to do with skipping gears in the center of the cluster. Getting to the small cog is likely a cable tension adjustment, since the chain seems to eventually drop onto the cog.
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Old 07-30-12, 12:20 PM
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To the OP, when you "relax" the left hand shifter (loosest cable tension), does the derailleur go to the smallest (7th) or largest (1st) cog in the rear? That tells us we're not working with a rapid rise (reverse spring) derailleur, which would change the diagnosis.

If it normally wants to go to 7th with loosest tension, then your problem is cable tension too loose (back the barrel adjuster out 1/4 turn and try again). If this only happens while under load, or happens in other rear cog positions, it could be a worn cassette or stiff chain link, as has been suggested.

In no case is it the limit screw.

If your derailleur wants to go to 1st with loose cable (reverse rise), then your cable is too tight, so the barrel adjuster must go clockwise 1/4 turn.
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Old 07-30-12, 01:49 PM
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Ok so here is what I did.. My friend brought up his bike and we took his RD off and put it on mine with his new chain, it still did it, we then used his back wheel with a 1 month old cassette, and it still did it. after that we started to put all of my original stuff back on when I decided to check the RD hanger like demon had suggested.. it was ever so slightly bent in. I called my friend I got it off of and he said he did lay it over and may have hit the RD the one time he did ride it after the tune up. So I took a straight edge and put it up to it and bent it back, I don't have the special tool to get it perfect but it is very close now. Sure enough after putting it all back together and adjusting it it shifts through all the gears perfectly and doesn't skip at all.

Thanks again for the help, I would never have thought to check the hanger.

On another note would the shimano st-ef51 ez fire shifters work for my setup or would I need a newer RD?
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Old 07-30-12, 02:34 PM
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Since you have 7 cogs in the rear you must stay with 7-speed shifters.

The sprockets in the front are called chainrings not cogs.
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Old 07-30-12, 02:49 PM
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Originally Posted by demoncyclist
Limit screws have nothing to do with skipping gears in the center of the cluster. Getting to the small cog is likely a cable tension adjustment, since the chain seems to eventually drop onto the cog.
Curious, tweaking the limit screws fixed the problem for me when it was skipping. Usually it skipped when it was in about 5-6-7 on the cassette, where 1 is the largest sprocket and 9 is the smallest.
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