Help! Urgent chain jump problem

[maurice]

Sorry for a gearing question but I've searched high and low for an answer and can't fix it.

I have an 07 Allez Triple, it came with a Shimano 12-25 cassette. I'm going on a tour so have fitted a SRAM 11-28 cassette and a new shimano chain.

I fitted the cassette ok, put the chain on, set the length according to parktool, gear shifting works fine. But whenever ANY load is put on the chain when it's on the small cog (11 tooth), the chain jumps badly on that sprocket.

I've tried shortening the chain - no affect
Tried changing the high limit screw - no affect (it's perfectly aligned)
Tried every b-tension under the sun - still does it at both ends of adjustment and middle.
I've also taken the cassette off the wheel twice and put it back on, making sure it's tight - no affect.

Can anyone offer any help, I'm off touring in 36 hours, would be very grateful.

 

[fossyant]

Could it be that the SRAM isn't a perfect match - what's the grade of chain - i.e. make and model ?

 

[maurice]

SRAM Cassettes - MTB PG830 Cassette 8sp 11-28
Shimano Chains IG70 Chain 8 Speed

Just to mention the 11-28 should in theory work as specialized now fit an 11-28 to the 2008 Allez. (the rear Tiagra is rated by Shimano up to 27 teeth high, 11 teeth low)

 

[mickle]

Sticky linky methinky. Put the chain in small to small to minimise the rear mech tension and turn the chain backards, you'll spot the stiff link as it passes over the top jockey.

 

[maurice]

Well just took it to the LBS and they found the problem!

My cassette lock ring was too big. (I used the lock ring off my old cassette as ChainReactionCycles sent me the new cassette without a new lock ring). Didn't realise they were different sizes for different cassettes.

They were lifesavers, never would have spotted that myself.

 

[maurice]

Oh and just to say, thanks for all the suggestions and help, appreciated!

 

[yello]

They were lifesavers, never would have spotted that myself.

I'm not sure I would have either, truth told. You live and learn.

Glad you're sorted. Enjoy the touring!