Rear mech issues

geoff93

Hi all, I’m having trouble with my Sora rear mech. It’s just not shifting well in the largest two sprockets. I can set the indexing perfectly for the others, however, if I adjust to get the top two working well, the rest are out of index. I’ve replaced the gear cable and outers, I’ve recently put on a new chain and cassette. The rear mech hanger is straight, I have checked with tool. Rear derailleur has been deep cleaned and relubed. Are we thinking rear worn mech?

pilot_pete

Is the B screw adjustment correct? Top jockey wheel is not too close on the big sprocket is it, partially jamming the chain?

redvision

You should only need to index the smallest sprocket on the cassette. When that's set up then shifting through the rest should be fine.

Have you checked the chain length is correct?

pilot_pete

Use the Shimano Dealer Manual for full instructions on how to set up correctly. If you follow all the steps from chain sizing to cable routing to indexing you should either get it working perfectly or have something that is worn out/ broken.

Then it is a process of elimination - the derailleur is dumb, it just moves in response to the cable pulling it. If with the cable removed, it moves freely in and out from stop to stop without excessive play and all the springs are working then it probably isn’t the derailleur at fault.

Is the loop of outer from the rear derailleur to the frame stop long enough? If that is too short it will affect shifting. Again follow the DM recommendation.

Is the cable clamped correctly? Just clamping it the wrong side of the clamp bolt can mess up shift pull and hence indexing.

If you remove the inner cable and fit a new one, did you feel resistance when pulling it out at any point? Is the old inner frayed or kinked anywhere along its length? Once removed, is the shifter dirty or gunked up inside? With the bar tape peeled back does the outer sit correctly in the shifter, and is it routing correctly with no excessively tight bend? If you pull it out of the shifter is there any wear around the shifter exit point or the entrance ferrule or outer cable end where it would sit in the shifter? This can show binding is occurring so treat the bike to new cables and use a proper cable cutter to get smooth/ square cable end cuts.

With just an inner threaded through the shifter with no outer cable, you can pull on the cable and operate the shifter through all the clicks. Can you feel resistance at any point or does it run through the right number of clicks up and down freely? This can prove/ disprove shifter operation.

Doing all this methodically can eliminate correctly working components and identify the faulty....good luck.

PP

thebigman

I have had this issue before.. have you made sure you secured the cable onto the rear derailleur the right way? If you don't route it correctly it will never index properly..