Rear Derailleur index shifting trouble
 

I spent an unsuccessful 4 hours today trying to tune an indexed-shifted rear derailleur.

First I set the H and L limit screws. I verify that the chain goes over all the cogs, but doesn't go over the lowest and highest cogs. But then the chain shifts erratically between gears. So I use the barrel adjuster to adjust the cable tension so the chain shifts on clicks. Usually this is all I have to do.

But now for the strange part: after that barrel tension adjustment the thing won't shift to the smallest cog. Even weirder, if I put it in high gear, reach under the downtube and pull on the bare shift cable, and then snap the cable to let it go, it shifts into the smallest cog. But if I shift out, it usually won't go back.

I'm going nuts.

Could this be caused by a bad or binding shift cable? Or do I need a new derailleur spring? Or could this be something else? The cables haven't been changed in about 10 years (about 6 of those it was unused). The derailleur itself is an old Alivio MTB model.

Need new cables and housings.

+1
You could try lubing the cables to get it to work, but that will just confirm that you need to replace them.

I had the same problem and the cable looked fine. Took to the LBS and he confirmed that the cable was just barely hanging on by a thread at the shifter. I'd say definatley new cable.

I replaced the cables and housings, but it still doesn't adjust properly.

But I did discover that the barrel adjuster on the derailleur is bent. The thing wobbles when I turn it. That's probably not good. Do they sell those things separately? (The cogs on the derailleur look straight.)

Here's what I tried this time:

- disconnect the cable
- shift into highest gear
- connect the cable with it taut
- adjust the (shifter's) barrel adjuster until I can shift into the second highest gear

but now it won't shift into the highest gear again! The derailleur moves a bit... just not far enough to actually move it. If I give it a gentle tap, it shifts right in.

Do I need a new derailleur? If so, any suggestions?

No need for a new derailleur. When you "connect the cable with it taut", you put too much tension on it. It needs to be just a little bit looser.

Try this:
1: shift the chain so it's on the second smallest cog
2: without pedaling, put the shifter in the high-gear position, i.e. the last click. You don't want the chain to go onto the smallest cog.
3: adjust the cable so all the slack it taken up, but not "twangy" taut
4: check that this adjustment allows for shifting between the #1 and #2 cogs
5: use the barrel adjuster in small increments to make sure that the chain is vertical through the derailleur and cogs in both gears
6: verify that the indexing keeps the chain vertical from cog to derailleur in all gears.

If this doesn't work, your derailleur my be worn out, derailleur hanger bent, or the cable may not be routed correctly. There's a couple photos at http://www.parktool.com/repair/readhowto.asp?id=64 that may help.

They do sell them separately. In fact, the LBS probably has 50 used ones in a bin, so it won't cost much :) Replace the barrel, unless you're pretty sure the derailleur is shot.

Derailleurs can get loose in the joints, so as a quick test, you can hold the derailleur at the lower pulley and gently push in and out. If you see and feel much slop in the derailleur's upper pivot and parallelogram pivots, then there's a limit to how precisely it's going to locate the pulley cage. In that case, pick up a new derailleur, and if you need help picking an appropriate one, post more info and/or pictures of your bike's current drivetrain.

I haven't tried Jeff's steps yet, but here's some photos of the derailleur.

BTW: There is some slop in the derailleur arm, I'm trying to figure out how to measure it.

Hmmm... the second image seems to show that the derailleur hanger is bent inward slightly. However, parallax may be throwing me off. Try taking another picture from directly behind the bike- the middle (4th) cog should line up with the middle (2nd) chainring.

Photo attached.

I think you're right. It does look a little bent inward.

I put the chain on the second front gear and the fourth rear gear. You might be able to see the handle of a little orange screwdriver handle sticking up above the chain. That's the second chainring.

I tried the above advice, but it still won't shift into the small gears reliably.

So I pulled off the hanger, cleaned it up, and put it down on the table. The hanger is almost as flat as the table! If it is bent, it's only by a couple degrees.

I'm hoping LBS has them in stock.

Well, I installed the new hanger and the derailleur looks somewhat straighter, but still it won't shift into the highest gear without coaxing.

I'm starting to think that the old Alivio derailleur is just too worn out to work properly. It seems like it just isn't pulling hard enough on the cable in the high gears. In fact, no matter how far I let out the H screw, I can't get the chain to run off the small gears into the frame (even after disconnecting the cable).

Maybe I just have derailleur envy, but it may be time for a new one. Any suggestions for something that will work on an old IG 7 speed? Can I just pick up any 8/9 speed derailleur?

Do the derailer pivots move other then the intended direction? If so, replace the derailer. A new Alvino would be fine.

I loosen the cable clamp turn in the barrel adjusters all the way make sure your shifter is clicked all the way down with the chain on the small cog replace the cable make sure its in the groove on the RD and straight it looks like it was before. When you have the cable clamped in take up the slack shift to the next gear adjust the barrel adjuster if it didn't move up to the cog adjust while turning the crank till it does, and make it nice and quiet, shift up 2 adjust if needed fine tune small turns shift up and down and check, adjust as needed this works for me.

May I ask is this a setup that was working before or is this something your setting up fo the first time? I ask because you could also have a compatabality issue "pull ratio" with that old MB derailleur and your shifter your using, just what is this combo?

JTGraphics - I can do all the steps you mentioned, but here:

When I adjust the barrel adjuster enough so it goes to the next highest cog, then it won't go back down to the highest gear. It shifts reasonably well though the remaining gears, albeit off by one.

(I can trick it into going down by either pushing gently outward on the cage or by pulling on and snapping the cable under the down tube.)

This has been getting worse for the last 500 miles or so. Except the cable, all the "transmission" equipment is original though, so it's probably not an incompatibility.

DieselDan
The top pivot wobbles in and out a small amount. I the wobbling top pivot to two other derailleurs. One is a year old SRAM, it doesn't wobble at all. The other is a low end Shimano, as old as mine but ridden less. It wobbles but a smaller amount.

I'm surprised how cheap the Alivio shifters are (at least at nashbar). The hanger from LBS cost just a bit less. I wonder if it would be worth a couple extra bucks to spring for the next model up.

Well at this point is sounds like you have done everything, so if you take the cable off and the chain with your fingers push the RD over how is the return strong or weak? possible return spring problem weak or broken. Check the shift lever and cable ends. Check cable for sticking for some reason did you replace outer casing? make sure the hole is round and not squashed. Don't take it for granted do a physical check I just say this because many times people will say yayaya because they were sure because they did the job but ends up being a problem.
Hay good luck hope you find the trouble.

Are the cable-pulls of the shifter compatible with the lateral-throws of the derailleur? Take a picture without chain of the RD in the smallest cog position and one in the biggest cog position. Rotate the cage so that the two pulleys are vertical and take a picture from directly behind the cogs so that the camera is centered on the cog that has the RD on it. With the older 6/7spd stuff, there's only a 0,25mm difference in spacing, but it adds up to large spacing differences between the two ends of the cluster.

By this do you mean going from smallest to bigger cogs isn't reliable, or only from big cogs down to smaller cogs? If it's the 2nd scenario only, it's a sign of insufficient return-spring tension in the RD or too much cable-friction. Did you oil/grease the new RD cables where they go into the housing? I find that the ferrule-ends without the o-ring seals work better, but require more frequent maintenance. Did you also clean-up or replace the plastic cable-guide under the BB?

At work I compared how wobbly the RDs on other bikes were (people probably thought I was crazy). None wobbled in and out from the top pivot as much as mine.

So I went to LBS and picked up a Alivio m410. It took about 2 minutes to tune the derailleur after the install!

Thanks for all the help guys!

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