Chain skipping gone weird
 

I finally got the Casati all dialed in, strung up the derailleurs and had some trouble shifting into the lowest gears, but eventually got it. Now, originally I had problems with the chain skipping and heard that I should move the wheel back a little in the dropouts, so I went ahead and pushed it all the way back. Kept skipping, so I replaced the freewheel with an almost NOS Regina. Since it was STILL skipping, I ordered new jockey wheels from Soma. Got it all re-done today, and guess what? My chain skips in the middle cogs on the freewheel.

My only current theory is that the chain is just the tiniest bit too narrow. It's an 8-7-6-speed Sram chain. Should I look into getting a(nother) new chain and seeing if that solves the problem? Any other ideas?

Assuming you are using friction shifters? Are you using an narrow style freewheel, to run 6 speeds in a 120mm frame? Sometimes a chain will be too wide for those and not seat on the center cogs. I've had trouble with Regina narrow sets. But it sounds like you have the right type of chain.

I've never had the opposite problem of too narrow a chain. But since you've replaced everything else I would at least try a chain off something else just to see if anything changes. Unless you have a very large low gear, having the wheel all the way back will not solve anything. Italian race bikes should have the adjuster screws all the way in!

No, the frame's spaced at 126. I had heard that the Nuovo Record rear der can be picky with the wheel too close up. I'll probably take it into the LBS where I work tomorrow and see if there are any other suggestions.

I had the same problem, did many of the same things you did with no improvement. Finally figured out that the chain itself had a couple of links that did not move freely like they should. When the stiff links hit the freewheel, all heck broke loose. A little penetrating oil and some moving the offending portion back and forth fixed the problem.

Tim, you said this happens in the "middle cogs." By chance are your friction shifters loose and move more freely in the mid range? If so the spring in the N/R RD might just be pulling the chain off to the next cog. Does it tend to only skip in one direction? Down to a smaller cog? The other possibility is that the RD is bent and the jockey pulleys not lining up with the freewheel cogs correctly.

I'd suspect the chain since you've dealt with everything else. I'm assuming what you describe is that it skips under a load, not self shifting as Bob describes? Is the derailleur fully tightened on to the dropout (and thus has no play)?

Neal

How many speeds? Indexed or friction?

I'm cheap, and use the HKK Z-Chains. I had a similar problem with the lower gears (high tooth-count) on a Miyata 210. Replacing the existing chain with a Z-Chain helped a lot, but the problem didn't go away until I replaced the 5 speed Sun Tour freewheel with a 6 speed (seems counter-intuitive doesn't it?) Shimano freewheel.

My money's on the chain. Try a new one.

My 83 Trek is doing the exact same thing, skipping in the middle cogs. I've had a new chain, and the chain that was on it when I found it. It only skips slightly less than with the new chain. New cables, and RD is an NOS Cyclone M-II. The shifter "wingnuts" are tight. Should I try the old BL?,,,,BD

I had skipping on my 84 Trek. I wracked my brain for a long time trying to figure it out.
I needed to tighten the bolt on the shifter. Doh!

Mine isn't jumping from gear to gear, it stays in one gear and jumps. Causes the crank to lurch forward while pedaling. The bike is IN one gear while doing this. I installed another helicomatic from my PH10 peugeot, and it was full speed ahead, no problems.,,,,BD

Cogs are shot I guess. Sorry not trying to hijack. My bike is doing the same thing that's all.

Huh, could be that the cage is bent. I'll check it out when I get home.

It's friction shifting and the lever is tight. 6-speed. The bolt is well secured. Also, it's not skipping to a smaller cog, it skips and remains in the same gear.

Had the same issue myself recently and as mentioned earlier in the thread it ended up to be stiff links in the chain. The problem was the chain would skip on some cogs (not all) it would not skip to another cog. Tried everything and as a last resort swapped out the chain which was only a week old..... problem solved. Why not give it a go?

385xza

No, I know the links are good. I've checked them all already.

Mine too, even had a new chain on it. It was worse with the new chain, lol.,,,,BD

Bent teeth on the cog? I don't know how it happens, but I had two on a freewheel that I got with a replacement wheel from one of the LBS's
I think I saw something about how to repair them on Sheldon's site.

Double check by hand the chain completely for a stiff link(s).
Check the derailluer hanger for alignment, often out by the way. The Shimano tool is best, from the SIS days.

Checking the cogs carefully, for bent teeth as stated and Cupping, depending on the ratio, that can happen to Reginas if somone attempted to take them apart, note the intercog spacing adjacent and between to all troubled cogs, its micrometer time. It can be very slight.

Unless you know the history of the freewheel personally, even a slightly used unit when run with a stretched chain can cause havoc.

Check the rear derailluer for alignment, best test is with the jockey wheels removed and with the parallellogram spring out, I have seen units that "look" good be bent from a wreck and or botched shift, rare, but what can happen is that at certian angles of the cage to the freewheel, the jockey wheels are not in alignment and the skipping is an "autoshift" in progress.

I'm thinking the derailleur's just shot. I'll double check the hanger, just in case. Grrrr.

I'm not sure what the adjuster screw is called where the RD mounts on the dropout. I unscrewed mine nearly all the way and it seem to help a bit. I still can't stand on it, but I can pedal harder than just cruising
on all but one gear.,,,,BD

Tim, can you take some close up pics of the RD, chain, FW, etc and let us take a look before you start adding to the landfill? Someone's eagle eye should be able to spot the cause(s) of your problem.

http://farm1.static.flickr.com/239/4...36e540b0_o.jpg

http://farm1.static.flickr.com/246/4...edd1607a_o.jpg

http://farm1.static.flickr.com/228/4...b8eda9b7_o.jpg


Let me know if you'd like any more pictures.

maybe not enough chain wrap? maybe add more links to the chain, or mess with the "b" screw adjuster if you have one.

edit: i don't see a b-screw (think this is what bikedued is refering to)

:beer:

Just added two more links to the chain (anymore and it'll be way too loose in the small ring), didn't get any better.

hmm...you said almost NOS freewheel? how NOS? those middle rings are the ones that usually get used the most.

:beer: