swapping from a 11-30 to 12-21 cassette problem
stevephillips
Posts: 10
i've got a problem with the new cassette i bought which should be a direct swap
its an 8 speed hg40 shimano and i want to change from the stock 11-30 to a 12-21 but having done this i get a vibration and knocking from the 12 and 13 cogs which is really bad. i thought as the stock cassette was an 11 cog that the derailleur wouldnt need much adjustment but i cant get rid of the vibration. the chain only has around 200 miles usage so cant see that being the issue. any help would be greatly appreciated.
its an 8 speed hg40 shimano and i want to change from the stock 11-30 to a 12-21 but having done this i get a vibration and knocking from the 12 and 13 cogs which is really bad. i thought as the stock cassette was an 11 cog that the derailleur wouldnt need much adjustment but i cant get rid of the vibration. the chain only has around 200 miles usage so cant see that being the issue. any help would be greatly appreciated.
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Best guess is that the upper jockey wheel is hitting the sprockets, presupposing the cassette has been put on the freehub correctly.stevephillips wrote:i've got a problem with the new cassette i bought which should be a direct swap
its an 8 speed hg40 shimano and i want to change from the stock 11-30 to a 12-21 but having done this i get a vibration and knocking from the 12 and 13 cogs which is really bad. i thought as the stock cassette was an 11 cog that the derailleur wouldnt need much adjustment but i cant get rid of the vibration. the chain only has around 200 miles usage so cant see that being the issue. any help would be greatly appreciated.
Try adjusting the b screw and perhaps shorten the chain.0 -
ive tried adjusting the b screw but it made no difference and would i need to shorten the chain if i run an 11 already?0
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Do a thorough visual inspection of the 12 & 13 teeth to see if any are bent or deformed.
Also check / clean the gaps between the cogs to make sure there isn't something stuck in there.
Jay Kosta
Endwell NY USA0 -
Not because you are running an 11 but because you are not running a 30.stevephillips wrote:ive tried adjusting the b screw but it made no difference and would i need to shorten the chain if i run an 11 already?0 -
freezing77 wrote:
Not because you are running an 11 but because you are not running a 30.stevephillips wrote:ive tried adjusting the b screw but it made no difference and would i need to shorten the chain if i run an 11 already?
Exactly this, shortening the chain will sort this out .0 -
ok so if i need to shorten the chain how much do i remove is there a set amount or trial and error start with one link and work from there? its a brand new cassette so theres no wear on it at all.0
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I use the Park tool method, with the chain removed put the rear derailleur into the highest gear and the front derailleur onto the big ring. Wrap the chain around the largest sprocket at the back and the big ring at the front, chain should go through the FD but not the rd (which is out of the way), bring one end of the chain (adding the quick link if you use one) to the point on the other end of he chain so that all slack is removed, add two links and break the chain there making sure the cut leaves the inner link so it can be joined to the other end. If adding two links gives the outer link, just add another link, it won't make much difference.0
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See link, largest sprocket t larges chainring method.
http://www.parktool.com/blog/repair-hel ... gth-sizing0 -
Shortening the chain may not be the issue(maybe though) After all you were not having these issues before in the higher gears were you?
On Sunday I went from a 11-32 to a 11-25 and its exactly the same in the higher gears.ie perfect The chain tensions that is.
The above may help but running a mix of worn and new bits has potential as well. Just check the smaller sprockets are on right as well.0
