running rough in high gears

chatlow

Have just put in a brand new 12-27 cassette on my scott road bike (was 12-25)

Noticed that in gears 12-15 there's lots of vibration/grinding coming from the drive chain. The chain isn't rubbing on anything. Happens on both big and small chainrings.

Could it be that the new cassette needs 'running in'? I didn't replace the chain as it's in fairly good nic and, although I would normally, it's a cheaper winter bike.

Any ideas?

diamonddog

Try checking the chain for any stiff links.

sungod

did you re-index the shifting? might need a tweak

otherwise, did you measure the chain for wear? i had a shimano hg-50 chain wear shockingly fast, looked like new but it was so far gone it trashed the cassette in a few months commuting

chatlow

Yeah I've indexed them pretty well. Can't find any stiff links but will check for stretched chain at lbs next week.

One thing I did notice was that the old cassette had a spacer behind it.. the old one doesn't. Should I fit the spacer? It's on at the moment

Thanks

sungod

ahhhhhhhh

what make/speed/model cassette?

chatlow

sungod wrote:

ahhhhhhhh

what make/speed/model cassette?

Cheap Tiagra HG50 9 speed on my Scott Speedster S40

sungod

as above, no spacer

noise/shifting issues in one area of the cassette can be due to misalignment with the rear mech or sticking mech/cable

first try these...

stand on drive side of the bike, lean over it so you can put weight on the saddle as you reach down to undo the rear qr - your weight will ensure the wheel is fully seated in the dropouts - keep the weight on as you do up the qr

on the same cog, the 15 say, does it sound equally rough if you've shifted from 16 as it does when youy shifted from 14? - reason to check this is that if the cable or rear mec is sticking a bit, alignment in the 16->15 shift is more likely to suffer than when shifting 14->15, the former is done only under spring tension, the latter is higher force

if that makes no difference, i'd wonder if the rear mech has had a knock and the hanger is twisted, it only takes a tiny bit to affect things, easy enough to check/adjust with an alignment tool, if you don't have one then it's a few minute check at a decent lbs

chatlow

Little update on this - removed the spacer and found that when tightened, the cassette has some movement in it so have put it back.

To explain the problem further.. the rough running is a harsh vibration that is felt on every revolution of the crank. It starts in the 16t sprocket and gets worse as you go down to 12t. Occurs in both chainrings

Have screwed in the b set screw (to make sure its ok in the 27t gear and the jockey wheels can be ruled out.

The gears are shifting pretty well.

Any other suggestions before I go to LBS?

Thanks

sungod

if you hang the bike off the ground, then turn the crank by hand while peering/poking (and avoiding losing fingers in flying spokes) you might be able to narrow it down

some hubs do have a spacer even for 9-speed, mavic for instance, c. 2mm thick

either way, sound like spacer is nothing to do with it

if you take off the wheel, can you feel any play/grittiness in the bearings?

Superbalicious

I hope you find the answer to this, because I have the exact same issue on my Ultegra 6600 setup. The vibration is very pronounced when turning the cranks clockwise by hand, disappearing as I shift up through the cassette. My shifting performance is otherwise perfect and to be honest I hardly ever notice it when out on the road, but I'm still perplexed by it...!

chatlow

Thanks, tried everything above (got a repair stand which helps diagnose a few things)

Appears the chains movement over the problem sprockets in question is very lumpy which causes a harsh vibration.

Perhaps a new chain is in order.

Been too busy playing with my new tcr advanced tonight but will try a new chain asap and go to lbs if its the same