gears help

[jann71]

Video of the issue - http://tinypic.com/r/v8fslt/4

Anyone know how to fix this?

LBS have just replaced rear cassette and new chain. If I push the rear mech back slightly it seems to be just far away not to catch.
If its something that just needs a tweak then I don't want to have to drag the bike back to LBS.

thanks

 

[Gerry Attrick]

It's difficult to see what's going on here as the video is so slow to buffer and does not show the chainset. However, I assume you are concerned because the upper jockey wheel is contacting the largest rear sprocket.

This occurs due to one or a combination of the following:

a) the "b" screw adjustment is incorrect;
b) the chain is too short;
c) you are using an impractical gear, e.g. the largest front sprocket in conjunction with the largest rear sprocket. This should not be used as the stress placed on the chain is excessive and causes rapid wear to your transmission;
d) incorrect derailleur cage size for the cassette you are using.

The "b" adjustment screw is the small, usually crosshead screw immediately beneath the derailleur pivot facing the rear of the bike.

Have a look here and here for help.

However, I would strongly advise you to take the bike back to your lbs as if you change anything and cause damage, they will gracefully bow out and leave you to pick up the bill.