Rear Derailluer Jumps sprokets under load

[antnee]

Hello Since getting the Winter bike out I've had some experience of the Rear derailleur Jumping up to a larger tooth sprocket on the Cassette. At the moment it seems that what ever I do when out on a ride R.e turning the adjuster screw to adjust tension on the cable in or out it makes no difference whereas when I put bike in work stand and set up it can be adjusted fine and changes gears correctly. the chain was new last winter and only saw minimum miles till end of last March The 9 speed cassette isn't worn though has done about 1,000 miles so that really wouldn't be a problem I wouldn't have thought, I haven't tested the cable tension as it seems tight enough. This is something that I need to address for sure, but Its surely not the derailleur itself though its an old Shimano Tiagra 9 speed I put on when I up graded the cassette from 8 speed to 9 last year. I can't think of anything else to tell you all other than Happy Christmas and I would appreciate any thoughts you might have on this matter.
Thanks very much

 

[cyberknight]

Have you tired adjusting it when riding ?
Mine always shifts slightly differently under load when riding compared to on the stand .

 

[antnee]

Yes did that yesterday But it was rather cold and fingers were a bit chilled so perhaps I didn't persevere as much as I would have it if it had been a bit warmer!

 

[screenman]

I take it that you have done step one and checked rear mech alignment, if not start there. Mine never jump regardless of set up on stand or riding hard.

 

[antnee]

Well I thought I had but I am always willing to start again with the whole process Will try that Tomorrow Thanks for that

 

[antnee]

So having been warm now and cleaned all the road muck off the bike got it out in the bit of sun we had the other day and up in the workstand, loosened off gear cable, refixed and then found the cable must have been to tight when in the top gear the 11 to 50 combination so was trying to drop to lower gear So have adjusted and been round the block a couple of times and so far seems ok but we will see. Meanwhile thanks for your input and wish all the people here a good Christmas and happy new year

 

[Globalti]

Good news but... that doesn't make sense! When on the 11th cog the cable is at its tightest and only the limit screw is preventing the derailleur from travelling further outwards. A slacker cable will allow the derailleur to move in to the next largest gear.

If you are having trouble indexing the gears the most likely reason is that the short length of cable outer curving round to the rear derailleur is rusted and crudded up and needs replacing. Get your LBS to cut you a few pieces to the same length and replace it regularly; giving the inner a good clean and some very light waxy lubricant at the same time. You'll be shocked at how badly the shifting has deteriorated without you noticing.

 

[antnee]

Thanks for the reply Globalti But I perhaps didn't word that sentence correctly What I meant to say was it was on the the 11 toothed sprocket on the cassette which has the least tension on it , we it does on the derailleur I have. Hence when on the largest sprocket i.e the 30 its at it's tightest

 

[Globalti]

OK but change that cable outer!

 

[antnee]

Yes I will it must grungy inside as it the same one from new in 2013. But I did put new cable in when I up graded the cassette from 8-speed to 9-speed and seem to think I must have lubricated it then. Cheers

 

[cyberknight]

I plan to put new jockey wheels on mine over x mas , they are very dirty and a bit noisy now .