Chain slipping issue

[Ernbar]

I recently replaced the worn chain in my 1974 Le Tour 10 speed. I went to my LBS and they sold me an SRAM PC830 8 speed chain. I asked about this chain being for 6,7, and 8 speed but they told me it works on the cassettes with 5 sprockets too. I installed the chain and all gears work fine except the smallest one on the cassette that slips under load. I looked at the teeth shape and they all look the same, squared at the top and I can't see any uneven wear. I usually don't ride in that particular gear but the next higher one. It wasn't doing this with the older worn chain and wonder if the chain they sold me is the correct one. TIA for your comments.

 

[GTs58]

That's a 1/2 x 3/32" chain and should work just fine. Sounds like a rear derailleur adjustment is needed.

 

[rustjunkie]

chain & cogs wear together and the smallest cog wears the fastest.

 

[Rambler]

I worked in a bicycle shop for many years and this is a common problem. The chain and sprockets wear together meshing as a set. Even though it may look OK to the eye, trust me, it's worn to match the chain you removed. On popular higher quality gear clusters you could often purchase individual sprocket. Replace the small gear sprocket with a new one and your problem will be solved. Typically it's only the smallest and sometimes the next smallest sprocket that you will experience this issue with because they have the fewest number of teeth so tend to wear the fastest. The larger sprockets have more teeth in contact with the chain so under load are less likely to slip even if they are worn some. You will need to replace the sprocket or put the old chain back on to eliminate this problem.

There are only a couple other things that can cause a slip or skip as you describe. (1) the chain link is stiff where the chain was joined together so that joint does not flex properly. Each time that stiff link encounters the small sprocket it slips. This can be solved by forcefully flexing the chain side to side to loosen that link. or (2) the derailleur limit screw is not properly adjusted so the chain is either being forced off the sprocket, chain is not riding properly on the sprocket. (3) Lastly alignment between the front crank and rear wheel sprockets is off so much it is not allowing the chain to ride properly on the sprockets possibly due frame alignment but I am ruling this possibility out because your bike worked properly before the chain replacement.

All this being said, I'm still convinced it's the combination of the new chain and old worn sprocket that is your issue.

 

[GTs58]

I really doubt the cog is worn on this beauty. Check the rear wheel alignment, the derailleur alignment and the derailleur adjustment. You have a bike stand?

 

[Ernbar]

I really doubt the cog is worn on this beauty. Check the rear wheel alignment, the derailleur alignment and the derailleur adjustment. You have a bike stand?

View attachment 1147699

 

[Ernbar]

Hey thanks for all the comments. Yep that’s my bike Gt and yes I have a stand . I will check things out tomorrow.
One thing that I was looking at was that to my eye, I see a slight cant to the left on the derailleur. I took a picture now and is more visible in person and in daylight.

 

[Ernbar]

If in fact the small cog is worn, can I just replace it instead of the entire cassette. I forgot to mention the rear small cog slips while using both large and smaller chainrings up front.

 

[GTs58]

When you say slips, you mean jumping off to the side of the cog? If that's what's happening it's not worn teeth on the 'freewheel', it's the derailleur.
I don't think Schwinn used cassettes during that time.

Do you have a straight on shot of the freewheel? You said the teeth are square at the top but in that picture it doesn't depict that.

 

[Ernbar]

When you say slips, you mean jumping off to the side of the cog? If that's what's happening it's not worn teeth on the 'freewheel', it's the derailleur.
I don't think Schwinn used cassettes during that time.

Do you have a straight on shot of the freewheel? You said the teeth are square at the top but in that picture it doesn't depict that.

Sorry Gt it's the freewheel. I keep learning stuff from you guys so thanks a bunch for the replies. The chain stays on the small cog but you can feel a jolt, slip or skip under heavy load.
I used my calipers to measure the teeth on the small cog and they are pretty consistent in size. Everything looks to be straight and in line so I guess the small cog has worn out as previously mentioned.