elcyc

I just replaced my chain (KMC x.99) with the exact same KMC chain, on my 21-speed Gary Fisher.
Concurrently, I replaced both rear derail. jockey pulley wheels with same Shimano models. I was careful in noting rotation and proper pulley position (upper and lower are different).
Everything looks aligned and true--the parts replacement went smoothly. I have done both procedures several times before on my Gary Fisher -- all w/o incident.

Except now, after replacing these new components, I am noting some significant "skipping" on the highest gears (smallest cassette cogs) (all this when PEDALING, i.e., CHAIN UNDER TORQUE). From what I could "see" when I looked at cassette while moving, the skip seemed to be the the chain "wanting" to shift left . The skipping is very apparent on the smallest cog. And the problem goes away from middle to largest cog.
I did some experiments with barrel adj.; made no difference.
It doesn't matter which front crank chain-ring I'm using.

On the other hand, smoothness and crispness has significantly improved. But that skipping is very annoying.

Later today or tomorrow, I'll try to do a full rear derail. alignment.
Till then, I'll let you all take dibs on what the problem may be!! Give me place to start!

jpescatore

Bent derailleur hanger.

Kapusta

If the previous chain was worn, then you probably need to replace the cassette as well.

New chain on a worn cassette does exactly what you describe. This is a textbook example.

I know it looks and feels like it is trying to shift up a cog, but what is actually happening is that the chain is lifting up of the cog.

blakcloud

I second Kapusta's comment. Your cassette needs replacing. While you are at it look at the chain rings because they may be next. I don't think it is your derailleur hanger if it worked before the replacement then it should be fine. Though it doesn't hurt to check as part of recurring maintenance.

Tandem Tom

When we check bikes in for repairs at the shop the chai is checked for wear. If it needs replacing I always tell the customer "A new chain doesn't want to play well with an old cassette/freewheel"!

nomadmax 

Look at every chain link as it goes around the top pulley while hand pedaling backwards. Could be a stiff link.

elcyc

Sorry, I already ruled out stiff link (should've noted this in OP). Again, no issues with middle to largest cog.

About cassette .... it is about 3 years old and shows very little sign of wear. My prev. cassette was replaced after 13 years of similar use, and it was only slightly worn in middle cogs.

With the troublesome cogs, if I step hard on the pedal while the bike is stationary, no skipping/jumping. Only happens when pedaling with torque.

An intriguing problem ....maybe some issues with KMC quality control (???) .... anyway, keep those guesses comin', folks!

Bigbus

Jeez, this could be a whole can of worms, but even though the chain is new, I'm leaning toward a fine tuning adjustment or a sticky chain link. Sticky chain links do that only on the smallest cog and only when you're pedaling under torque. Good luck and let us know what cured the problem when you get it solved, and I'm sure you'll get it solved haha.

CoogansBluff

I'm having a similar issue. Just got a new chain and new derailleur, plus new cables and wiring. The cassette is maybe 6 months old. The skipping was really bad on the first ride. Took it back and got it re-adjusted. On the second ride, it was much better, but still had probably 10 skips over the 30-mile ride. Might take it back for another adjustment. I can't do it myself.

Trakhak

The skipping on the small cogs means that the likelihood is nearly 100% that the cassette should be replaced to correct the problem. The smaller the cog, the higher the number of times each tooth on the sprocket is subjected to abrasion from the chain. Also, if you used the previous chain until it was elongated past its recommended maximum, you shortened the life of the cassette accordingly.

At this point, you can investigate other possible explanations, but you'll end up replacing the cassette after none of the other fixes work.

By the way, my guess is that most of the people saying that the cassette needs to be replaced are (like me) former or present bike store mechanics who have much more experience diagnosing this and similar problems. You see the same division of opinion in "I installed a tube and it turned out to be defective" threads. It's funny how seldom bike store mechanics encounter defective tubes and how often novices do.

Koyote

Quote:

Originally Posted by Kapusta

If the previous chain was worn, then you probably need to replace the cassette as well.

This.

elcyc

The prev. chain replacement was concurrent with cassette replacement (June 2017).
I don't ride hard or in dirty environments (city commuting; no real grades; 30 lbs of pannier cargo + me 135 lbs) ....and I'm pretty religious about cleaning and lubing and routinely CHECKING for wear, maint. and alignment issue.
BOTTOM LINE: I have mostly babied the Gary Fisher!

Get your guesses in ... I have made a few adjustments, and will hit the road soon. Pedaling on the bike stand shows promise .... but the road ride will reveal all evils!

On a side note: i did not lube the brand new chain. The buttery smoothness I noted in the OP is to be relished like a fine vintage.

Trakhak

"no real grades"; in your list of particulars, you left out the fact that you use the small cogs mostly or exclusively.

woodcraft

Yeah, most likely a bad chain- that happens a lot.

But also could be a problem with the pedals, or maybe a bump in the tire, or one of those jockey wheels was bad.

Also, it was just full moon...

OK, my guesses are in.

chadtrent

Just another thought - did you make sure the number of links in the old chain was the same as in the new chain? I have seen chains that are too long behave like you are describing.

79pmooney

3 year old cogs. New chain skips under pressure on the small ones. I'm 95% certain this is worn cogs. (If you can see the wear that cog is very worn.) Buy a new cassette. If the skipping still occurs, I"m wrong. Come back and scold me. But I won't be holding my breath.

With this new cassette and chain - measure the chain often. (Steel tape measure. Measure 12 pairs of links, pin forward edge to pin forward edge, New, this is 12" exactly, When the chain "stretches" to 12 1/16", replace it. (Keep it marked as that bike, date and 1/16") Do the same with the next chain, And so on until a new chain behaves as your current chain is acting, ie skipping, Now our cassette is too worn for a new chain but all your old 1/16" chains will work. Use them until each chain hits 3/32" or shifting becomes poor. Now it's new chain and cassette time again but you will have gone a lot longer on that cassette and saved some money.

Ben

elcyc

The new components act fine on a bike stand, pedaling at the smallest cassette cog. I even simulated added torque applying small amount of brake.
All power transmission and gear shifting, on the stand, is smooth and crisp.
BUT ... the problem remains on the road under actual conditions. Essentially, the three smallest cogs (on the HG50 7-speed cassette) are now useless.
I did notice that the skipping is worst when torque is light to moderate. If I apply the brake slightly to increase torque, the skipping reduces.

I'd have to say that in the 27 years I've owned this bike -- over a dozen chains, and three cassettes -- this is the first time I've encountered this issue.

AGAIN: On the stand ... what issue ? ?

Trakhak

Any guesses how many more times the OP will ask the question before finally buying the new cassette?

79pmooney

Again, try a new cassette. (Or just replace the outside 3 cogs if that is possible. I run Campy 9-speed where they are separate cogs, I've never owned Shimao or SRAM so I"m no help there.) You are describing what I am talking about. And yes, typically the chain passes the test on the stand, even applying the brake, but shows on the road when you need it to work. (Or put your old chain back on. You have missed the "window" of being able to put a new chain on an older cassette. This window closes first for the small cogs where only a couple of teeth take the full load of the chain. Once there is enough wear, the distance between cog teeth is greater than the distance between the chain links.) You could also just ride what you now have until the chain stretches enough to work on those worn cogs. Might take a couple thousand miles. I wouldn't have the patience but it can be done.

Ben

elcyc

Mid-2004 to mid 2017, I ran a 7-speed HG70 Deore cassette (very high quality -- the don't make it any more, so I had to settle for HG50).
Alas, the HG50 7-speed is no longer avail. (I haven't searched extensively, tho')
Suggest some alternatives please.
Some views of the Shimano HG50 7-speed 13-23 cassette I'm using (these photos taken today)....

elcyc

One thing about both the HG50 cassette ... the three troublesome cogs are not part of the HG "unit", per se. (Same as my old HG70, and maybe common to all HG). In the 17 years I've used HG, the smallest three cogs always had a very tiny bit of slop (can wiggle with fingers) despite the fact that lock-nut was torqued to specs. The 4 larger cogs are are UNITIZED to the HG body.

Trakhak

If you want to stick with 13 to 23 for the cassette, you might have to do some digging. First thing I'd do is ask at a local bike shop, especially if it was already in business back when 7-speed cassettes were commonly offered on racing bikes. If the shop doesn't have one in stock, they can always check with one or more of their suppliers. Quality Bicycle Products (QBP) is always a good bet.

CoogansBluff

Any signs that this cassette would need replacing?

woodcraft

You need a shim behind the cassette to take up the slack. There's a slight chance that this would help the skipping.

elcyc

I already use a spacer ring behind the cassette ... both the HG70 and HG50 required their use with the Deore wheel I use.
As far as the slop ... it is extremely small. I can reduce it by over-torquing the lock-nut. But I'll never be able to remove the damn thing ... been there, done that.