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Chain Skipping on Rear Cassette

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Chain Skipping on Rear Cassette

Old 06-14-15, 07:20 AM
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Chain Skipping on Rear Cassette

I have just about come to the end of overhauling my DB Topanga. I have replaced the crankset and chain and when I took it out for a test ride this morning, the chain was skipping on the rear cassette when under load. It seems fine when changing gear carefully and when not putting the gears under pressure. But when I start to push on the crank - such as on a hill - the skipping starts.

I have replaced the Shimano FC MC12 44-34-24 crankset with a Shimano Acera FC M361 42-34-24 version and replaced the SRAM PC830 chain with a Shimano HG40 one and both look the same. I kept the number of links the same for the new chain as I had on the old one. And I have done nothing to the rear cassette or derailleur other than clean them. I did not remove the cassette or derailleur.

The cassette does not look worn to me, but here is a pic:



Can anyone advise if they think this cassette looks worn? Or does anyone have any idea what could be causing the skipping?
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Old 06-14-15, 07:24 AM
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To me the cassette looks badly worn and is your problem. Roger
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Old 06-14-15, 07:27 AM
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A cassette which skips with a new chain is due for replacement. You cannot tell wear condition by visual inspection unless it is really trashed. The fact that it does not work is all you need to know.
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Old 06-14-15, 08:12 AM
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As a general rule, a well used chain and cassette have to be replaced together. A new chain will almost always skip on a high mileage cassette unless the chains have been replaced very frequently in the past. As noted, you cannot tell the condition of the cassette by inspection unless it is obviously damaged.
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Old 06-14-15, 08:42 AM
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Originally Posted by dsbrantjr
A cassette which skips with a new chain is due for replacement. You cannot tell wear condition by visual inspection unless it is really trashed. The fact that it does not work is all you need to know.
I concur. It just takes a little bit of wear to create a mismatch that leads to skipping under load.

Once I had a bike that was skipping like the OP's. As an experiment I tried replacing single parts. Then I tried every combination of replacing just two of the three drive train parts. No go. I had to replace the entire drive train in that one case.
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Old 06-14-15, 10:57 AM
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Many thanks, guys. I did suspect that would be the case. The cassette was changed a couple of years back and to me it didnt look bad but I do accept that the wear could be 'between the teeth' and therefore difficult to identify.

New cassette to be ordered then!
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Old 06-14-15, 11:49 AM
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Originally Posted by rodscot
Many thanks, guys. I did suspect that would be the case. The cassette was changed a couple of years back and to me it didnt look bad but I do accept that the wear could be 'between the teeth' and therefore difficult to identify.
As noted by others, new chain/old cassette is a classic and predictable cause of skipping. In most cases the only remedy it to replace the cassette. But if the skipping is slight and only occasional, it will heal itself and resolve if you simply ride the bike. The remedy is to wear off the back corners of the teeth a tiny bit so they clear the rollers as the chain arcs into place as it winds onto the sprocket at the bottom.

If it's skipping badly you'll run out of patience before it resolves, but if it's rare enough that you can live with the problem a bit, you might give it a chance. Also, if you have less patience, but do have Dremel tool, you can grind a bit off the rear of each tooth on the offending sprocket.
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Old 06-14-15, 12:35 PM
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Originally Posted by FBinNY
As noted by others, new chain/old cassette is a classic and predictable cause of skipping. In most cases the only remedy it to replace the cassette. But if the skipping is slight and only occasional, it will heal itself and resolve if you simply ride the bike. The remedy is to wear off the back corners of the teeth a tiny bit so they clear the rollers as the chain arcs into place as it winds onto the sprocket at the bottom.

If it's skipping badly you'll run out of patience before it resolves, but if it's rare enough that you can live with the problem a bit, you might give it a chance. Also, if you have less patience, but do have Dremel tool, you can grind a bit off the rear of each tooth on the offending sprocket.
Thanks, I have ordered the cassette now as I thought that since I had done so much work on the bike, then it would be daft to risk damaging the chain - or anything else. The bike can be ridden if ridden carefully, but when confronted with a sudden hill or incline, then a sudden change down under pressure would mean having to get off the bike and wheel it up the hill.

It is a pity that I did not plan for this as I would probably have opted to change to an 8 speed cassette and would have been able to buy the right chain, new shifters, etc before doing all the work on the bike. A lesson for the future!
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Old 06-14-15, 12:46 PM
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Also make sure you don't have a kink in the chain.

Either run it through your fingers, bending every link, and make sure they straighten back out... or slowly crank it through the derailleur and watch for the links to hop as they go around.

If you find a stiff link, then you can loosen it by pushing the pin with the upper shelf in your chain tool, or sometimes work it out with wiggling and oil.
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Old 06-14-15, 03:05 PM
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Originally Posted by CliffordK
Also make sure you don't have a kink in the chain.

Either run it through your fingers, bending every link, and make sure they straighten back out... or slowly crank it through the derailleur and watch for the links to hop as they go around.

If you find a stiff link, then you can loosen it by pushing the pin with the upper shelf in your chain tool, or sometimes work it out with wiggling and oil.
Thanks, I had a quick look earlier today when I first noticed the problem and the chain seems ok. I will give it a more thorough check tomorrow morning.
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Old 06-14-15, 03:30 PM
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Is it skipping in all gears or just a few? Most cassettes don't wear evenly, so its usually only a few cogs that are bad. If it skips equally in all gears something less seems more likely.
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Old 06-14-15, 03:33 PM
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Originally Posted by gsa103
Is it skipping in all gears or just a few? Most cassettes don't wear evenly, so its usually only a few cogs that are bad. If it skips equally in all gears something less seems more likely.
From memory it seemed that 4,5,6 did it but 7 was ok as were 1 - 3.
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Old 06-14-15, 05:59 PM
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Originally Posted by rodscot
From memory it seemed that 4,5,6 did it but 7 was ok as were 1 - 3.
Yes, time for new cassette. The middle of the cassette usually wears the fastest since you tend to ride more there and smaller cogs wear faster (fewer teeth to engage).
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Old 06-26-15, 09:49 AM
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Originally Posted by gsa103
Yes, time for new cassette. The middle of the cassette usually wears the fastest since you tend to ride more there and smaller cogs wear faster (fewer teeth to engage).
I've been running my commuter bike as a makeshift singlespeed (chain fixed on one cog in the existing cassette). Last night I installed a new rear derailleur and chain to convert to a 1x6 configuration. The cog I'd been using in the single speed setup is now skipping like crazy, but all others are fine. D'oh.
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Old 06-26-15, 11:15 AM
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Probably with normal riding, there are a couple of preferred gears that will wear faster than the others. Depending on your cassette, you may be able to source individual sprockets. I got a few singles (pairs) from Road Bike Mountain Bike Bikes on Sale Bike Parts, Bike Gear - CambriaBike.com for quite cheap. Or, perhaps E-Bay.

Did the new cassette fix the OP's problem?
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Old 06-26-15, 12:08 PM
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Can someone describe to me what chain skipping feels like? I am not sure if I'm experiencing it or not on my bike. Is the chain physically sliding over the edges of the cogs when you pressure hard?
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Old 06-26-15, 01:51 PM
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Originally Posted by mozad655
Can someone describe to me what chain skipping feels like? I am not sure if I'm experiencing it or not on my bike. Is the chain physically sliding over the edges of the cogs when you pressure hard?
You'll know when it skips. When you're pedaling smoothly, you'll feel a slight jump, a similar feel to when you're shifting gears. If you're under heavy pedal load, sometimes it will jerk forward abruptly. It's pretty annoying, much like a creaking bottom bracket or squealing brakes.
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Old 06-26-15, 03:15 PM
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Originally Posted by CliffordK

Did the new cassette fix the OP's problem?
Yes, the new cassette worked a treat for me.
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Old 06-26-15, 03:23 PM
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Originally Posted by rodscot
Yes, the new cassette worked a treat for me.

Great!

For me, I noticed immediately when my chain was worn. The ride felt... gritty, slippy? even after I cleaned the entire drive chain. I could just FEEL that there was something off with the chain. Sure enough, I tested it with a chain tester and it just cleared the .75 mark (or is it .075... i can never remember.) I replaced the chain and it felt 100x better. (And shifting improved.)
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