Chain skip....redux...again :)
 

I was here about a month ago regarding some issues about chain skip (http://www.bikeforums.net/showthread...1#post14291182)

I haven't been able to completely rid myself of it. The problem seems to be only in 7th gear (11-28 cassette). With the "B" adjust set to one end, I seem to get no skips when riding on flat ground. At the other end of adjustment, I get very occasional skips (no obvious pattern tied to links or cassette/crank rotation...tho it may be because it's not obvious :( And these particular skips don't seem quite like skips. Almost as if the chain momentarily hesitates to settle back onto the 7th gear (if that makes any sense). However, if I "stand" on the cranks when going up a hill or over a bridge, I definitely notice a nasty skip.

I have adjusted (and readjusted) the derailleur and can't quite completely eliminate the skip. Chain and cassette are now about a month old (brand new when this all started). I have adjusted Hi/Low limit screws as well as the adjusters at both the derailleur and shifter (shifter is Shimano SIS). Shifting is crisp (easily within 1/2 pedal stroke) up and down.

I know the standard procedure is to adjust the "B" screw so that the "jockey" pulley (one closest to the cassette) barely clears the lowest (in my case, 28T) gear. However, I can't tell any difference when I adjust this screw (other than a bit more tension).

I never had this problem before. The 2 things I changed are: 1. New jockey pulley - old one had a lot of side-to-side and up and down play in it (still not convinced it was worn out...tho with over 18K miles...maybe). May have caused some "slow" shifting from 6th to 7th gear, but never any skipping. 2. Cassette - Got a "low end" replacement (supposedly Shimano, but it only says that on the lock ring) because it's not easy to find 7spd, 11-28 cassettes these days. The chain is new, but it's the same chain I had on the bike.

I'm tempted to think it's the cassette. I may reinstall the old pulley. I will go back and try some more adjustments on the "B" screw and see if that makes it better (before I start tearing the rear section apart again).

I would welcome any insight or suggestions anyone can offer (my frustration is starting to build....)

Thanks and cheers....

Is this "indexed" shifting, or old style friction shifting ? If indexed, make sure the new upper pulley is for an index system, because they are supposed to have a bit of float in them.

Chain skip....redux...again :)
 

The SIS I mentioned in my post is Shimano's indexed shifting (A number of years ago I upgraded from the "friction" Grip twist shifting that originally came with the bike and have had no problems till now).

The originally pulley had lots of "slop" in it. The replacement pulley has ~1/8" side-to-side play.

If either of these were an issue, I would expect to have problems in some of the other gears, as well. This seems fairly specific to the 7th gear.

Thanks for the thoughts, tho.

Rather than scrolling back through the other ones, can you remind us if it occurs on both (all) chainwheels or if not which ones? Thanks.

You probably already have checked, but if not, the high limit screw is out enough?

Chain skip....redux...again :)
 

@cny-bikeman

The bike has 3 chainwheels (I've come to know them as chainrings). I pretty much (almost always) ride on the middle one.

@RaleighSport

I have had it loose and also firmed it up a bit. Doesn't seem to have any effect on the skipping. Altho, it's one of the things I'll go back and check.

The rear derailleur is a Shimano Alivio. Has 18K+ miles on it but still seems fairly tight on the pivots (parallelogram).

It feels like there is something subtle here that I am missing. I'm wondering if the older, and looser, jockey pulley is needed because of the design nearly 15 yrs ago, and that the newer, tighter pulley cranks down the tolerances too much for this older technology. Wouldn't think so, but then......

Has the bike fallen on driveside recently? I'm just wondering if the hanger or the RD itself might be bent?

When faced with problems I could not solve in my old manufacturing days, rather than look for "the" solution, we would just brainstorm and create a list of everything we had not tried, even stuff that seemed to have nothing to do with the problem. When we finished, we discussed which ones would be easiest to try, and we started trying them. Invariably, by the second or third item on the list, the problem would be solved.

The key was bringing up ideas we had all dismissed earlier. Solved a lot of big problems with this simple approach.

Well, that does not really tell me if the problem occurs in the large chainwheel (the granny of course is not useable with small cog). It does tell me you are riding the middle cog with the small chainwheel. Under stress it may not take very much to put things out of line due to frame or chainwheel deflection. It's also a terrible gear for wear. Unfortunately the stupid decision of Shimano to extend a 7 cog cassette from 11 to 28 teeth means you have a relatively large gap in between gears, and therefore may not have an equivalent gear with the large cog - but it does not hurt to check with Sheldon's gear chart. I would have advised you to get a 13-28 instead. The 11 is as useless a cog as I've ever seen.

As for the jockey wheel or derailleur, you have to think about this logically. The derailleur is in much more solid a position on the small cog than in the middle gears, laying against the high limit stop, so one would generally expect fewer problems there, especially after trying different screw positions. The biggest difference between the small cog and others is the angle and the small number of teeth, so the most logical cause would be related to one or both of those in combination with the chain.

Skipping under heavy pedaling load is almost always a symptom of worn chain OR cassette, or both.

Could also be a broken axle.

I don't know how I missed this before.

Even with the middle ring you're pushing a gear ratio that should generally not be used unless you are already up to speed and have run out of the other cogs - certainly not for routinely climbing. Go ahead and use it if you wish, but you will run into problems - noise, skipping or wear - no matter what adjustments you make.

Thanks for all the feedback and suggestions.

Without rehashing too much of my previous thread here's a quick summary of how this all started....

This skipping problem began when I replaced chain, cassette and pulleys on the rear derailleur, about 1-2 months ago. Prior to that I was running an HG-60, 11-28 7spd cassette, just like I have now, and had no problems (other than a bit of temperamental shifting from 6th to 7th).

Recently cleaned and regreased the hubs and everything seemed fine. New cassette (HG30 11-28), new chain and I replaced the pulleys with what I thought were a top and bottom pulley I purchased in a set. Almost immediately I had serious chain skip, even in 6th gear. I put back on the old cassette, no change. Swapped out the chain, no change. Thought about the new cassette but I finally figured out that the pulleys I purchased were both bottom pulleys, so I had a jockey pulley that wouldn't jockey.

Ordered up a new Shimano "Centeron" pulley, installed it and went thru an adjustment process: Hi and Low Limit, B adjust, and barrel adjustment on cable at both derailleur and shifter. I have been able to eliminate skip when riding on flat land, but have not been able to get rid of it when doing some sort of climbing.

Again, this problem wasn't there until I started to replace parts.

I have fallen on the bike (water on paint and slick wood, sand/loose gravel), but not since this problem started, and never on the derailleur side of the bike.

I can eliminate the chain because it is supposedly the same version (SRAM - old: PC-58, new: PC-870) of chain I had on before, and there are no kinks or stiff links.

At this point, I can only figure it to be 1 of 2 things (I think I mentioned them above..but I am always open to suggestions :) The cassette is supposed to be Shimano, but is it possible that Shimano sells their lockrings and someone is using it on an inferiorly designed and mfg'd product? The lockring is the only thing that says Shimano. The other is the jockey pulley. The old one had a lot of play (sideways and up/down/front/back). New one...just sideways. The new pulley makes the shifting really nice...but I wonder.....

@wrk101

You must be very familiar with "Occam's Razor", I suppose ;)

Again, to summarize, none of this started happening until I began replacing parts. The pulleys were an obvious one at the beginning. However, I'm not sure what to do except maybe put the old pulley back in and see if the problem goes away. That pretty much leaves the cassette as the issue, but that may not make sense either. tho, I might just put the old cassette back on just to satisfy my curiosity.

Again, I appreciate any and all input. I will take the suggestions offered and check them out to see if I missed something.

Cheers....Steph

OK, so this may end up bring a "Well, duh!!" kind of moment......

I readjusted the "B" screw to the opposite extreme (mostly out) and that seemed to minimize the chain skip on flat terrain (when I had it most of the way in, the skipping was worse). While on my ride this morning, another thought occurred to me.

In my original posting I believe I mentioned that the derailleur is the one that came with the bike. That means it is ~13 yrs. old and has 18K+ miles on it. It's also Shimano's lower end product.

While I realize anything is possible, for those in the know about deraillers, how probable is it that the derailleur spring(s) could have lost its/their tension? Is it possible the skipping problem could have been "masked" until I put in the new jockey pulley, which tightened up the specs?

I know running an 11T gear can be a challenge in some situations. I have been running the 11-28 set up for ~5 yrs. without any problems (before I replaced the jockey wheel). It seems to me that tension in the chain/derailleur is pretty much critical to ensure the chain is well-seated on the gears, especially an 11T, which kind of pushes the limit.

I'd be interested to hear of any one else's experiences with derailleur spring fatigue.

As usual, thanks for the taking the time to help out.

Cheers....Steph