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So...
My sister wanted a new bike, her partner got her a second hand liv (giant) bliss 2 in almost brand new condition and dropped it to me for a 'quick' service.
Set the rear mech up, fine. Set the front mech up, fine. Checked the rear mech again and it wouldn't shift down smoothly. It appears that the rear mech is only aligned correctly when in the middle or top front ring but when i drop down to the small ring it wont shift correctly.
Any ideas what the hell is wrong? I've checked for damage, wear and tear, chain length and can set up the rear mech to work in the smallest front ring but it then doesn't work in the larger two!
Any help would be much appreciated!
Is the rear mech hanger straight? (or indeed frame)
Internal gear cables ?
I would probably try a new rear gear cable as a starter , if you are sure chain is not too long ..
If you have internally routed cables, i'd suggest one of the inners is wrapped around the other inside the downtube, so shifting the front mech up puts tension on the rear, shifting it down releases it. Ive experienced this countless times on Trek's earlier this year, thankfully they seem to have it sorted now.
Thanks for the suggestions! Replaced cable including adding a bigger loop of outer at the back as this seemed a little tight. No better. Hanger is straight. No internal cables.
Mech looks straight and is basically brand new but has a lot of side to side play. I'm thinking this is the issue. In the largest front ring everything runs fine, middle its ok but a bit rough, smallest ring its shite. Would this make sense? The extra tension the rear mech is under in the bigger rings is reducing the amount of play in the mech?
Play in the mech would usually result in poor shifting all round, but you might be right. You could try turning up the b-tension and see if that makes it any better. But, if it is caused by play then it will probably be because of the angle the chain comes onto the tension jockey pulling the mech over in the granny ring. Quite unusual, though.
If it is that, you could try putting loads of grease into the bushings and tightening up the pivots with vice grips, but your probably better off getting a new mech
Has it got bolt on cable guides? A mate had similar on his boardman and it turned out to be the bolt on guide pinching the outer on the boss.