please help to identify rear dérailleur size

aripallaris

Hi all. so I have been having problems with my rear derailleur. My chain drops out of the jocket wheels. I popped into a store today and the mechanic told me it was because i was running a 12-25 with a medium rear mech. He checked and re-adressed a slight misalignment in the hanger. Ultimately he said i needed to get a smaller derailleur or larger range in the cassette. I like my 12-25. has all the gears i need for speed and climbing. before i spend another £60 + £15 fitting (also need it done before sundays london to southend ride) i need a little advice.

Now i know i specifically ordered a short rear dérailleur with my groupset. Is there a way to check which one i have installed? I think i may have had the wrong one shipped out and its gone un-noticed.

gozzy

Was he a salesman or a mechanic? Running a 12-25 and a medium rear mech is fine. As long as your chain is the right length, and it's all set up right it should work.

To see what size mech you've got have a look on the body of it for a model number and then google the model number and see what it says. Shimano are GS and SS for long / short cage

aripallaris

Can't find any model number. It just says ultegra 6700 .

keef66

Look at the exploded diagrams on Shimano Techdocs, you should be able to see the 2 different cage designs and work out which you have.

http://techdocs.shimano.com/media/techd ... 753764.pdf

Having said that, I'm running a 12-25 cassette with a long cage 105 mech and a triple chainset, and my shifting is spot on.

Your LBS bloke isn't talking complete rubbish; you do get slightly slicker shifting if you use a shorter rear mech. But it doesn't explain your chain dropping off the jockey wheels (?? How is that even possible??)