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SRAM 8 Speed chain and cassette issue

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SRAM 8 Speed chain and cassette issue

Old 06-22-09, 06:39 AM
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DaJMasta
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SRAM 8 Speed chain and cassette issue

This is something I only recently became aware of, on a long ride through relatively poor trail conditions, using a PG-850 cassette and a PC-850 chain. Both SRAM, both 8 speed, but I've been having problems with one gear: the 11 tooth high gear.

Basically, because the 11t ring is so small, any dirt or gunk between the 11t and 12t gear will cause the chain to skip in 8th gear intermittently, and I'm ok with that because I'm not sure there's anything that can be done about it, but after cleaning it I noticed that there are marks from where the rollers contact the inner shell of the cassette, which is obviously not a good thing for the chain, for the cassette, or for fixing my top-gear chain skips.

So basically, has anyone else had this happen and do you have a solution? The only thing I've been able to think up would be moving to a 9 speed chain (they're a little thinner, so the rollers could be a little smaller and thus not contact the cassette inner shell), but I don't know if the reduced width of the 9 speed chain would work as well with my 8 speed setup. My front chainrings would be fine, but the cassette teeth may be too wide.

And finally, why would they build parts which are not compatible with their own matching-series parts? Sure the 12t variants work fine, but this is rather annoying....
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Old 06-22-09, 11:27 AM
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When's the last time you replaced your chain/cassette? Have you measured your chain to check the wear? I've used a variety of 8 speed SRAM chains and cassettes and have never had a problem.
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Old 06-22-09, 04:38 PM
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Sounds like a B-screw issue.
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Old 06-22-09, 06:33 PM
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The chain and cassette are both about 2months old, maybe a bit more than 500 miles on them. And by B screw do you mean the High limit screw on the rear derailleur? I've got that backed out quite a bit and have tried it with many settings from almost low enough to down-shift to far off in the other direction.
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Old 06-22-09, 07:22 PM
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Here's a good start (and finish I hope):

https://www.parktool.com/repair/readhowto.asp?id=64

And...

https://bicycletutor.com/adjust-rear-derailleur/

From your description I think we can safely rule out the chain & cassette. And don't get a 9-spd. chain - this will just give you a new set of problems. So something directly pertaining to the rear-derailleur (RD) is out of adjustment. How is your cable-tension going to the RD? If it won't shift to your smallest cog - 11T - this could indicate that the cable-tension is too high. So try undoing the pinch-bolt on the RD and relax the cable a bit. Not too much - it needs to be taut just not too tight. Then tighten the pinch-bolt - 48 - 60 inch pounds - and run it through it full range. First read below here:

If this works - be careful. If you have been playing with the hi-low screws, you may need to re-set these so your chain doesn't get led to either fall off the cassette and get stuck in the frame - or get thrown into the spokes.
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Old 06-22-09, 07:55 PM
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Originally Posted by DaJMasta View Post
The chain and cassette are both about 2months old, maybe a bit more than 500 miles on them. And by B screw do you mean the High limit screw on the rear derailleur? I've got that backed out quite a bit and have tried it with many settings from almost low enough to down-shift to far off in the other direction.
You need to learn how to do a proper rear derailleur adjustment instead of winging it. See above post.
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Old 06-22-09, 08:04 PM
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Well if there was any doubt before, I am a semi-competent mechanic and while I appreciate the help, I have tried tuning and retuning my derailleur (was done several times before I even noticed the wear). In it's current state, it properly shifts between all gears (though the tension is somewhat slack so it shifts up a bit faster than down usually) and the high and low limit screws are set so that it will stay in gear.

The chain slip problem I am having with the 11t gear is infrequent and only happens when pedaling extremely hard (up a hill or from a stop, and only in top gear). I know it has something to do with the depth because of dramatic changes in frequency when something was caught in there to when it was comparatively cleaner. Perhaps I can clarify with a picture:



You can see between the 11t and 12t cog indentations where each roller contacts the central shell and a line where the sides of the link seem to be touching it as well (did not see that earlier...). It's not terribly clean, and I will relube it when I put it on the bike (still getting the trail dirt out from my last ride), but I know this shouldn't be happening.
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Old 06-22-09, 08:08 PM
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You don't seem to understand what we're trying to tell you. From your description, you have no idea how to do a proper rear derailleur adjustment. Follow the parktool instructions and go top to bottom without skipping steps. It is possible your B-tension screw isn't adjusted properly, you have a bent derailleur hanger or the chain and cog combo is actually worn enough to cause skipping. Another possible cause is too long chain length.

It would also be easier to show us a picture from the side of the cogset. The top down view doesn't tell you anything. The other question is why the heck are you pedalling up a hill or starting from a stop in the 11t? You're either extreme cross chaining or put out more wattage than hoy.
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Old 06-22-09, 10:03 PM
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Originally Posted by operator View Post
You don't seem to understand what we're trying to tell you. From your description, you have no idea how to do a proper rear derailleur adjustment. Follow the parktool instructions and go top to bottom without skipping steps. It is possible your B-tension screw isn't adjusted properly, you have a bent derailleur hanger or the chain and cog combo is actually worn enough to cause skipping. Another possible cause is too long chain length.

It would also be easier to show us a picture from the side of the cogset. The top down view doesn't tell you anything. The other question is why the heck are you pedalling up a hill or starting from a stop in the 11t? You're either extreme cross chaining or put out more wattage than hoy.
Please don't just tell me I don't understand because we seem to be talking about different things. Yes, my B-tension screw was maladjusted, I have since fixed it, but that and to some extent the chain skips are a side note in the scope of the thread, what I'm concerned with is the wear on the cassette in a place a cassette should normally see no wear. I posted a picture of a side view because I am not concerned with wear on the teeth of the cog, but on the metal which holds the cogs together, between the 11t and 12t cog specifically. I only mentioned the high and low limit screws and my changes to their adjustments as a reply to indicate that I had tried reconfiguring them already, I know where they should be (and have them set up properly, even reading through the park directions to be sure), but I tried to move the high limit screw out when on a pit stop while riding to reduce the skips on the high gear, trying to perform a quick-fix to a problem I wasn't sure what was causing.... that's why one of my posts gave the impression of them being misadjusted.

And I am pedaling in my 11t because I like to go fast and I don't like to shift, somewhat just to push myself. Perhaps it's a single-speed mentality, but I try to stay in my highest gears and pump my legs accordingly; I am very much not a sit-and-spin rider.

Now, please, can anyone comment on the wear between the cogs?
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Old 06-23-09, 03:57 PM
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Chain bottoms out between the 11T and 12T on my 8sp sram too. I only use the 11T while hauling ass downhill, rarely ride through mud and have experienced no ghost shifting problems.
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Old 06-23-09, 06:49 PM
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Originally Posted by DaJMasta View Post
Now, please, can anyone comment on the wear between the cogs?
What part of, that picture doesn't tell us jack**** don't you understand? Measure your chain and post the results or seriously, what exactly are you expecting?
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Old 06-23-09, 07:08 PM
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Originally Posted by DaJMasta View Post
Now, please, can anyone comment on the wear between the cogs?
You've said yourself that you've had dirt and gunk in there. My guess is most of the wear is attributable to that alone. Also, if you do a lot of standing and pedaling while using the 11T cog, I can tell you from experience that you will wear out the cog teeth very quickly.
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Old 06-24-09, 12:29 AM
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Originally Posted by joejack951 View Post
You've said yourself that you've had dirt and gunk in there. My guess is most of the wear is attributable to that alone. Also, if you do a lot of standing and pedaling while using the 11T cog, I can tell you from experience that you will wear out the cog teeth very quickly.
Just seems like an odd place to find wear, I expect the sides of the cogs but I guess the fact that the chain fully contacts the inner wall is a bit alarming.

I will definitely keep an eye on the 11t cog for wear on the teeth though, it makes sense that it would wear out faster but given the conditions and my riding..... 'style' it's probably worth looking out for.

Anyone know if you can buy just the 11t cog? On both cassettes I've had the 11t has been separate from the rest of the cassette, is this specifically for replacing when worn or is it an ease of manufacturing/installation thing. Could be a nice affordable replacement when I see some wear on the sides or if I just run out of ideas and it's still slipping.
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Old 06-24-09, 06:28 AM
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Unfortunately, unless you run one of the higher dollar Shimano cassettes (XT/XTR) individual cogs are not readily available. It seems like a big waste but given that 8 speed MTB cassettes are so cheap, you might as well just replace the whole thing.
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Old 06-24-09, 12:21 PM
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Originally Posted by joejack951 View Post
Unfortunately, unless you run one of the higher dollar Shimano cassettes (XT/XTR) individual cogs are not readily available. It seems like a big waste but given that 8 speed MTB cassettes are so cheap, you might as well just replace the whole thing.
True enough
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Old 06-24-09, 12:46 PM
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It appears to me that the chain is contacting the spacer between the 11 and the next larger cog. This is not the hub shell. That should not be happening and can only mean the chain and the 11 cog are not compatible or worn out. If you have the wrong lockring on the cassette it could explain chainskip on the 11 but that would not explain the chain contacting the spacer. The 11t cog must have the special 11t lockring.

I do not think derailleur adjustment is the primary problem.

Be sure to measure the chain for stretch. A 24 pin interval of new chain measures exactly 12 inches. By the time any 24 pin interval measures 12 1/16 inches it should be replaced. If you replace the chain and the skipping continues you probably need a new cog and maybe a new cassette. Do you really need an 11?

Al
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Old 06-24-09, 03:05 PM
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An additional note to what Al said is to make sure your cassette lockring is fully tightened to the recommended (high) torque. I think it's 40Nm.
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