Gears jumping.

andyrr

Just wanted some pointers :
Commuting bike has had a fair bit of use through the winter, chain was well worn so far so I decided, just as the bad weather hit, to renew the transmision :
New chain, cassette and chainring.
It's running Tiagra 7 speed, chainring is a TA one.
Also greased the rear wheel bearings.
Since doing all that the bike hasn't been outside but has done a good few spells on the turbo - a different wheel used with a TT specific tyre.
Riding to work this am and the chain jumps like hell on the cassette, only a couple of sprockets has it running ok - 3rd largest and maybe smallest ones, even then it seems to 'tick' away but at least I can put pressure on the pedals without it jumping badly. It seems as if I can 'hold' it in a gear with the RH STI lever and it then runs ok.
Puzzle then - I'm pretty certain the chain is the correct type, it was a new Shimano one I think (with normal pin, not quick link).
A click on the lever doesn't always result in a change of sprocket at the rear it is adjustment / cable no? One thing is the rear mech jockey wheels are pretty worn - not quite sure if these could cause such behaviour ? I've had problems with the rear mech not pivoting properly (seizing up) but it seems to move smoothly enough.

simonaspinall

Just try resetting the cable tension first.
Stick in in top gear on the cassette/crank
Undo the rear derailleur cable
Screw/Unscrew the barrel adjuster so it has about 5-6 threads showing
Pull hand-tight (pull so it's tense but not too tight)
Tighten the cable holding screw

To test and fine-tune (Assuming your drive side of the bike)
Put the bike in a stand
Turn the crank and change the cassette gear to the 2nd smallest cog.
If it doesn't change try turning the barrell adjuster away from you to loosen it, about 1/2 turn.
If it still doesn't change, slowly turn it until the chain moves.
If it struggles going further up the cassette just do incremental turns away from you
If it struggles going back down the cassette turn the barrel towards you slightly (like fine tuning a guitar)

You're aiming to get the tension correct so that the cage sits directly under the cassette cog. Watch the allignment as you turn it and you'll see it move, this should help.

I'm sure there is a youtube vid or something to help you if you get stuck.

Apologies if it sounds like im teaching you to suck eggs. :-)

skellator3

sounds like you need to re index the gears

andyrr

Yeah, it did appear like bad cable tension/indexing/cable not free so I'll give it a look tonight, just wondered why it was ok on the turbo (different wheel) and not on the road, plus if the worn jockeys coudl be influencing the behaviour.

simonaspinall

Prob best to try that first...if it doesn't then jocket wheels are pretty cheap and it never hurts to replace them.

If it STILL doesn't work then it's either the derailleur itself (could be bent?), worn cassette (unlikely) or chain (unlikely).

Even if you had to replace everything, with the level of drivetrain you're running it shouldn't be a costly business - And it will be shiny and new!

Meds1962

While you're at it it would not take much to change the mech cable and make sure there's no gunge in the small section of outer next to the mech.

andyrr

Fettling last night has improved things so it is about 80% ok. Added difficulty is that the adjuster on the mech is seized into the mech (result of a plastic bag getting tangled in it one day) so it's a case of loosening the clamp bolt then pull some cable through)
Still get the occasional nasty 'jump' from the rear but way better then yesterday.
Will investigate possiible remaining issues inc new inner and outer cable (think these are fairly new, can't recall for sure) plus I want to double check that the chain is a 7-speed compatible one in case I've used a 9-speed that I had in the wrong box in my store of bits.
Other thing is that the hub/freehub seems to be 'dragging' as when I lift the rear of the bike and turn the pedals to spin the wheel then I stop pedaling, the wheel seems to not spin totally freely and pulls the cassette around and hence the chain which causes the pedals to continue to turn slowly. Not sure if that's due to using wrong grease in the hub itself (white lithium I think) or maybe the freehub is knacked/needs greased.

darren H

look at the deralleur from the back. If its angled a bit it could have been bent. Easily done. Usually bent inwards
If it is try just bending it outwards so its level.

Sorting out gear indexing can be a saga