LeicaLad 

A few photos below.

New chain, new 7s Uniglide cog set, skips on the 3rd cog only.

Now why would it do that? Chain line is essentially at its best. No issues in, on, or off any other cog.

This is a new wheel set with a DA 7400 hub and a standard 7s cog set from NOS cogs. A very low mileage SRAM 890 did the same, only on cog 3, and I swapped out the chain.

Uniglide has these mixed height teeth in some cogs, or are these actually broken? I’ve seen enough that I presumed it was part of the design.

Does “lining up the cogs”, such as by the stamp mark happens to leave such “stubs” adjacent to one on the next cog. Would that matter?

These feel like exceedingly dumb questions, but I cannot figure this out. I cannot replicate the skipping on the stand. Only under pressure, even modest pressure.





Just pull the cog and change? But I want to understand why it is happening.

Thank you for any insights.

AnkleWork

Maybe lube the chain?

bigredkevbot

Make sure your cable tension isn't too tight. If it's skipping on a couple teeth on the cog that may be your issue. check to ensure the chain is in-line with the cog (the teeth would ideally rest in the middle of chain).

Homebrew01

This is friction, non-indexed setup ??

I am guessing that due to a Campy rear derailleur with Shimano cassette.

I would start by riding it and getting it to skip. Then, without touching the shifter or anything. Put it on the stand and pedal, looking at the chain and derailleur and alignment with the cog, and look for anything bent, out of place etc ...

Is the rear derailleur meant for indexing, so the upper pulley has some float, allowing the chain to move a bit side to side ?

LeicaLad 

Yes. All C&V content. Friction, Suntour bar-cons.

Again, it is slipping only on the 3rd cog, where the chain line is actually as straight as possible. The chain is brand new from the wrapping and is lubbed and even Teflon coated. But this occurred with a SRAM 890, too. Also well lubbed. ONLY on the 3rd cog, a 21t, new cog.

So, feathering back and forth doesn't seem to secure the lock down. I guess there is something in that cog's specific teeth, but it is not logical and I see nothing amiss beyond those odd "stumpy" teeth.

Those ARE normal on UG cogs, yes?

Bill Kapaun

Try flipping the 3rd cog and see if it makes a difference.

LeicaLad 

Thanks. That's next. But if it works, I'll be even more mystified. I just can't figure why on that cog, and not reproducible on the stand?

Will do the cog flip or swap next.

FarHorizon

Last time I had a third cog skip, the adjacent cog was slightly bent, deflecting the chain when I tried to shift to #3 . The chain would shift down to #3 without issue, but when trying to shift up, it skipped maybe 30% of the time. I'm sure you've looked at the adjacent cogs, but just in case...

Bill Kapaun

I'd be less "mystified", since the other direction may have zero to < wear.

hueyhoolihan

occasionally, when i start entertaining really off the wall type of situations, i go back over things that i have previously ruled out as not possible, looking for something that i may have assumed was true, but wasn't.

hueyhoolihan

it's very hard to duplicate a problem that only manifests itself under load, when the bike is on the stand.

LeicaLad 

Cogs are new, meaning less than 100 miles. Chain is new, meaning less than 10 miles of shake down.

Under careful and magnified eye-balling, I see nothing crooked, bent, nor nuthin'

I'll flip 'em first, then I'll swap out for other NOS cogs.

Just strange. Thanks for encouragement as I go.

ljsense

Since this problem happened with your other cog set (the SRAM one you mentioned) I'd be surprised if it were related to the cogs.

And since it happens under load, I would think about things that might change with pedaling force.

Maybe your frame is flexing and applying force on the shift cable. I don't know why that would only affect the third gear, but maybe this is the one that's most eager to shift, since the chain is neutral here and easy to bend in either direction.

Also, maybe the cable housing is doing something as you pedal. Bar end cable housing is pretty long and can do stuff when you're riding.

Just a few quick ideas for your consideration

FBinNY 

New chain/old sprocket is classic for shipping.

With wear the rollers create pockets at the base of the teeth. That allows the chain to settle deeper and the next roller ends up bumping the corner as it meets the teeth. That causes it to climb up and ride the top, until the pitches line up tha the chain can engage. That's why you get the one link skip.

If the skipping is very minor and you can live with it, ride the bike, and the bumping roller will wear the offending corner, and the problem will solve itself. Or you can use a Dremel to break the back corners of all the teeth on the problem sprocket, and solve it immediately (but it's a slow process).

ljsense

op says both the cogs and the chain are new, and the same thing happened on a different cog set that had low mileage

ljsense

Can you check the alignment of the derailleur hanger?

LeicaLad 

Same cogs, different chain. It's a new wheel. NOS cogs. NEW. Did a couple modest rides with SRAM chain. Skipping on 3rd cog. That chain was a few months old, very modest mileage. Thus, the cogs maybe have 100 miles, but I'd guess less. That SRAM chain, maybe 500-600 miles. Darn near new.

But, I still traded that out for a Brand New fancy schmancy Wipperman chain. Same result.

I'm swapping around the cogs, but can't get out to test right now. (Duty bound.) Derailleur has been no problem on other wheels, mostly 6s or 7s Freewheel equipped.

It's an odd one.

FBinNY 

I missed the second "new".

Then it's probably a simple profile or stiff chain issue. Since it's only on a single sprocket, I'd see if I could live with long enough for break-in wear to fix it.

ljsense

whoops i misread. try a different cog set

LeicaLad 

Thanks. I'll flip the cogs to see if it is the same, but I may try the "patience" route next.

As always, thank you for the generosity of suggestions.

ThermionicScott 

Could you take some dedicated pictures of the "stumpy" teeth? I was under the impression that Uniglide teeth were all the same -- full height and twisted.

LeicaLad 

Solution achieved, but mystery remains.

A new set of cogs and it shifts flawlessly. I got a quick 30 mins. out for a sprint, and nary a single slip nor chatter. Can't make it skip.

When I pulled the previous cluster off, I'd forgotten that the upper five cogs were pinned. Yes, I could unpin them, but it was easier to quick grab a group of loose cogs and throw 'em on. Also all NOS cogs. SO, the obvious answer is that there is something among those pinned cogs. That was a NOS set I'd purchased a while back. Who knows what warp or pinch, but my eye hasn't seen it yet. I've looked from every angle but still stumped. I'll take it apart on a cold night.


Ask and ye shall receive. The short and slightly wider teeth seem to appear only on the 21t and larger cogs. I've just dug through a box of new cogs, including a set pulled from box and virgin wrapping plastic. They all have them above 21t.

Two photos.





Both images the same two 21t cogs. This was Q&D.

They have another on the other side, but not directly.

ThermionicScott 

Thanks! Given that they're in the same position and cut straight across, it must be intentional -- probably to aid shifting. I've learned something new, and am going to re-inspect my Uniglide freewheel(s) to see if it/they have similar teeth.