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PostPosted: Sat Aug 03, 2013 2:49 am 
Retro Guru

Joined: Sat Jul 14, 2012 8:23 pm
Posts: 973
Location: Kent, UK
Hi to all

Am slightly perplexed as I've just built up first road bike for one of the kids, and it's running an 8spd Veloce groupset.

The cassette is a little worn looking, and is jumping on the smallest two cogs when pressure is applied (climbing type pressure) through the cranks. It doesn't jump in any other cog.

Is just that these two cogs are knackered and I should simply replace the cassette? Or could it be an adjustment issue? Spent quite a long time adjusting the rear mech and it shifts well, smoothly and accurately across the whole cassette.

Am running it with a virtually new 7700 Dura Ace chain which is a 9 speed I believe (just in case the change could possibly be the issue), which is virtually new and not stretched/knackered in any way.

Many thanks for any thoughts!


Last edited by rjsdavis on Tue Aug 27, 2013 1:44 pm, edited 2 times in total.

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PostPosted: Sat Aug 03, 2013 7:28 am 
rBoTM Winner
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Joined: Tue Apr 25, 2006 12:06 pm
Posts: 1443
Location: Vienna, Austria
Could be a number of issues....

1. Chainline, sometimes chains will struggle to sit on smaller cogs when front chnger is in higher outer-most setting due to poor chainline.
2. Lockring, if your smallest cog is a 11t then you will need a specific lockring, don't forget that lockrings usually come with hubs rather than cassettes.
3. Travel limit adjust, thisis the small screw which sets the spring fall rate of the cage on your derailleur, if this is set poorly it will prevent your chain sitting properly on the smaller cogs.


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PostPosted: Sat Aug 03, 2013 11:34 am 
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Joined: Tue Oct 16, 2012 4:16 pm
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Until last week I was having exactly the same issue - after playing with the limit screws etc it was working as should be apart from when climbing / out the saddle or really giving it some on the flats - brand new chain but I was using an oldish cassette - didn't look worn and had equal wear across all cogs. Installed a fresh out the box cassette and hey presto, all sorted. I've learnt that new chains don't work with 2nd hand cassettes or freewheels.


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PostPosted: Sat Aug 03, 2013 1:26 pm 
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Joined: Sat Jul 14, 2012 8:23 pm
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Location: Kent, UK
Thanks for these replies. Just to clarify my own vagueness, when I described the smallest two cogs, I actually meant the smallest two gears, ie the largest two cogs on the cassette or the 19 and 21 teeth cogs in this instance. They jump like crazy going up a small incline with moderate pressure and whilst in the saddle... the jump is so significant that you couldn't trust it to get out of the saddle without doing yourself a mischief!

The cassette is a fairly standard 12-21 8 speed affair, so I don't think it will be the locking suggestion above. Chain line looks as it should when viewed from behind the bike, and as mentioned it all shifts perfectly up and down the cassette, so would be confident that the derailleur adjustment screws are pretty much where they should be, otherwise there would be shifting issues at either end of the cassette range typically (ie not quite wanting to shift onto the final cogs properly, or worse wanting to jump off and extended range and go too far). At least that's what my gut is saying. My instinct is that the cassette is knackered, but still keen to explore any other potential issues that could be the cause.


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PostPosted: Sat Aug 03, 2013 6:42 pm 
Old School Grand Master
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Joined: Fri Oct 14, 2011 8:41 pm
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Location: Cumbria
Ah! Does it happen with the chain on the large chainring.........in a perfect world you should avoid "crossover" gears as the chainline is at quite an angle.

Shaun


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PostPosted: Sun Aug 04, 2013 12:17 pm 
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Joined: Mon Mar 26, 2012 5:21 pm
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My first thoughts, from your description, would be wear in the drivetrain.

A 9 speed chain on an 8 speed set-up won't help; I'd get rid of that for a start: Shimano chains don't have the best rep anyway, Wipperman/Connex would be my recommendation.

More likely to be the (alloy) chainrings, than the (steel) sprockets that have worn, especially if we are talking about the larger ones: obviously the smaller sprockets wear faster, assuming your cassette is well balanced and you're using all of it.

As ever, a picture paints a thousand words: chainrings and sprockets please.


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PostPosted: Sun Aug 04, 2013 5:10 pm 
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Joined: Sat Jul 14, 2012 8:23 pm
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Location: Kent, UK
Midlife wrote:
Ah! Does it happen with the chain on the large chainring.........in a perfect world you should avoid "crossover" gears as the chainline is at quite an angle.

Shaun


Thanks Shaun, but sadly occurs in both chain rings. Son is very frustrated as I can't let him out on it yet as he'll never climb anything steep with his smallest two gears out of action!


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PostPosted: Sun Aug 04, 2013 7:02 pm 
Old School Grand Master
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Joined: Fri Oct 14, 2011 8:41 pm
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Location: Cumbria
Bang goes my theory of a problem with chain "crossover".............next thing is slightly mismatched chain / casette due to wear or design.

Shaun


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PostPosted: Mon Aug 05, 2013 10:49 am 
Dirt Disciple

Joined: Mon Jul 15, 2013 6:48 pm
Posts: 65
I would have said worn chain (stretched), worn cogs or both.

If the chain is worn or stretched you may well see gaps between the links and the teeth of your chain wheel.
If that looks ok check for the same on the rear cogs you are having the issues with.
If you can see gaps between the links and the cogs teeth then the chances are the cogs are worn.

Also check wheel alignment.
I had this sort of issue on my MTB and mine was due to the wheel not being aligned correctly.


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PostPosted: Mon Aug 05, 2013 11:11 am 
Old School Hero
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Joined: Sat Mar 16, 2013 12:14 pm
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Location: Durham/Northumberland border
I've had this too, and I run 8 speed Campag on my Denton road bike, and a new cassette and chain together fixed this instantly.

Sticking me neck out here, but if you are using the original Campag 8 speed setup (top left in this link) http://branfordbike.com/articles/casset ... s-pg60.htm and not the later Exa Drive setup, then in theory you should be able to remove the cassette and reverse the largest 2 cogs so they are 'inside out'. Not the best technical fix I know, and it probably won't do anything for the smoothness of shifting, but if it makes a difference then you are closer to confirming the cause of the problem.

Just a thought...


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