Rear mech issues

[finch]

XT 10s rear mech with 5700( old style cable runs ) shifters

Shifting down the gears ( to larger sprockets ) beautifully - nice and quiet

Not coming up the gears at all - 5 maybe 6 shifts and it drops some sprockets but won’t “release” one at at a time or even all the way - cable is running smoothly through the housing so I’m sure it’s a mech issue but I don’t know what it could be

My 4700 rear mech won’t do because it has a different pull ratio apparently

[ElyDave]

I have a similar issue with mine running the same set up on my Fairlight.  Although they are the same pull ratio, I find I can set it up to work well on most but not all gears, so I accept that I need the middle to work all of the time and can accept that I need to trim manually at either end.

I suspect that it could be overcome with a thin shim, but have not tried that yet.

[finch]

See that’s the kind of thing I get fixated upon if I’m out cycling

I have a “spare” 6700 rear mech in my box that I was keeping in case I ever needed it for my bestest bike but I’m probably going to have to use it - don’t really want to put it on my winter hack because they’re getting hard to find but it seems to me that the XT rear mech just has a weak spring out the factory

[grams]

Are you sure that’s what you have? 10 speed road and MTB mechs have completely different pull ratios and shouldn’t work at all. Maybe it’s a 9 speed mech?

(Also if you have flying gear cables that’s 5600)

[finch]

Could be a 9sp rear mech and yeah it’s 5600

Anyway the 6700 rear mech has sorted the problem but I might try and find a 5600/5700 rear mech so I can stick it back in the parts box

[ElyDave]

Are you sure that’s what you have? 10 speed road and MTB mechs have completely different pull ratios and shouldn’t work at all. Maybe it’s a 9 speed mech?

(Also if you have flying gear cables that’s 5600)

5700 10sp is the last cross-compatible with the MTB rear mechs as I understand it.  Mine is definitely 10sp

[Dickyelsdon]

10 speed MTB, branded 'DYNASYS' have a different pull ratio so not compatible with 10s Road stuff as mentioned above. However likely not the issue here if it shifted up the gears ok.

Why is it hanging shifts? 
Could be excess chain wrap or a stiff new chain.  A stiff chain and derailleur designed for a wider range cassette can end up held in gear if the top jockey wheel ends up more in-front of the cassette rather than under it, leading to a lot of chain wrap and leaving the derailleur in a place where the spring doesnt quite have the leverage needed to fight the chain down to the next gear.  Adding B-tension or removing a link from the chain can help.  A mech designed for a wider range cassette than its being used on can result in the installer reducing b-tension to bring the jockey wheel closer to the cassette. 

All or none of these may apply depending on the details of the set-up, cant say for sure.