Gear change problems

[helston90]

For the sake of argument I'm looking for help on my rear cassette and will simply refer to them as smaller or larger cogs.

I watched a You tube on setting up my index shifting Shinamo gears, did as it said removing cable, adjusting to centre on small cog and reattach cable, shift to a next cog up and adjust tension until it shifts- and it works- it's amazing, it flies up, and when I shift to next big cog it flies up again- success...I thought.

It now won't go back down predictably, I sometimes have to change twice and go back up, or change gear and spin until it drops.
Any one got anything thoughtful hints or tips on what's causing this? Or am I just a bit rubbish at setting up my gearing?

 

[MrJamie]

My understanding is that when you shift to a bigger sprocket it pulls the cable hence derailleur directly into that position, when you shift to a smaller sprocket it just releases a teeny bit of cable allowing the spring to pull it back to the next smallest sprocket. It could be that theres a little too much tension so its very eagerly being moved up, but isnt quite released enough to move back down, or it could be that theres some resistance somewhere in the cables, like if its routed under the bottom bracket and all crapped up or if the cable outers have become unseated somewhere when you released the cable.

Reminds me I've had brand new rear cable sat on my desk for about a month and havent got round to replacing it yet

 

[lpretro1]

Fit new cable inner and outer - it is almost certainly dragging somewhere between shifter and mech

 

[accountantpete]

Shifting down at the rear relies on the rear mech spring. Give that a good squirt of WD40 and make sure it is moving freely by itself.

The shifter should be ok - there is a small spring inside which gives the cable a nudge in the right direction.

So that leaves the cable - inner and outer.

The outer should be smooth flowing with no sudden curves. Also the ends should be cut square and with no squashing and I pop a little ferrule on each end of every segment to make the chain of contact that bit more firmer. Make sure that the outer cable runs firmly and fully into the shifter.

The inner should be clean with no strands of frayed wire - a dab of oil iside the outer cable does no harm either.

 

[HovR]

For the sake of argument I'm looking for help on my rear cassette and will simply refer to them as smaller or larger cogs.

I watched a You tube on setting up my index shifting Shinamo gears, did as it said removing cable, adjusting to centre on small cog and reattach cable, shift to a next cog up and adjust tension until it shifts- and it works- it's amazing, it flies up, and when I shift to next big cog it flies up again- success...I thought.

It now won't go back down predictably, I sometimes have to change twice and go back up, or change gear and spin until it drops.
Any one got anything thoughtful hints or tips on what's causing this? Or am I just a bit rubbish at setting up my gearing?

Start by winding in the barrel adjuster a small amount at a time (removing tension from the cable) until the derailleur predictably shifts down the block. If at this point it will no longer shift up the block predictably, or you just can't get it to shift down predictably at all, then see below. If this has fixed the issue, all good!

Check your cable. Remove the cable from the rear derailleur and check that the inner slides freely with little friction inside the outer cable housing. If there is an issue with the cable, it is most likely to be the section of cable where it bends around from the frame to the derailleur.

If this is full of gunk/rust it creates too much friction causing poor shifting, simply replace your gear cable (both inner and outer, although the outer nearer the handle bars will most likely be fine - worth checking anyway though).