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.

andrewgturnbull

Hi there.

11-28???? Is that a mountain-bike cassette? I'm going to take a wild guess here, but maybe your rear derailleur isn't capable of changing across such a large range. Have you got a short or medium length cage? You'll probably need a long cage for that cassette.

If this is the problem, then there may be too much slack in the chain when you're in the 11 tooth.

I'd stick the 12-25 back on if I were you.

Cheers, Andy

maurice

Hi Andy,

The Tiagra rear mech is rated up to 27 teeth by shimano, but many people say this is conservative and Specialized themselves spec the 08 Allez with a 11-28 cassette, so it should bloody work!

08 Allez - http://www.specialized.com/bc/SBCBkModel.jsp?spid=33694
07 (mine) - http://www.specialized.com/bc/SBCBkMode ... spid=21890

According to their site its a Tiagra long cage on both.

I'm beginning to lose faith though, you may be right, Could do with that 28tooth rear for going up the Alps with panniers though :?

RichTL

My allez triple works fine with a 28 large cog on the rear cassette. Can only suggest two possibilities 1/chain length not correct or 2/wrong chain type ie 9 speed chain on a 8 speed cassette. Sorry I cant be of any more help.

maurice

The length is in the right range I think, looked at all the diagrams on sheldon/park/shimano etc.

You may have got something with the chain type though. Even though CRC said it was 8 speed, and it had 8 speed on the packet, it was an absolute bitch to get an 8 speed SRAM powerlink on it :?. Needed circlip pliers and plenty of abuse to get it snapped in.

I've never had an issue with powerlinks before.

RichTL

Hi Maurice
It could be the power link thats the problem. Have you checked that that particular link?
is it free and not too tight. If too tight it could be causing the problem.

Good luck

maurice

I thought that Rich but it was fine when in place. The chain will jump at any position on that 11tooth sprocket too, even if the powerlink is nowhere near.

andy advanced

how worn was your last chain? its possible that your old chain was worn to a degree that it started wearing your chainset so the new chain "slips" the teeth on the chainset..if you get me

always_tyred

You are going to need a new chain eventually, so invest in one now to see if it solves the problem.

Its not clear from your post (and often isn't clear per se) if the chain is skipping across the 11 tooth, or periodically trying to jump up to the 12. It feels the same, more or less, under load, but you should be able to see it as you ride (and just before you cycle into a tree - so be careful!)

If its going to the 12 it could well be one of the links or the range of the rear derailleur. You would expect it to be worse the smaller the ring used at the front.

A long shot - but check the cables where they run through the shifters. Sometimes they fray, the shifting seems fine but, under load you expose the additional stretch in the cable. Should manifest in different parts of the cassette as you adjust cable tension, which doesn't seem to be the case.

It does sound to me that your chain is just on the way out, though.

meagain

Long shot. Check the teeth on the 11: are they all "vertical"? One or two bent ones will I think cause such trouble.

maurice

Thanks for all the suggestions guys.

I was out of ideas so took it to the LBS first thing 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