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I'm having issues indexing my gears. I'm not new to this - have been indexing gears since I got rid of thumb shifters in the last century - but I've not seen this one before.
It's fine going 'up' the cassette i.e. to the bigger sprockets but when I go down there's a lag. If I want to drop down a gear I have to drop two and go up one.
I've cleaned everything, changed the chain (was due one) and used a new cable, set it all up again from scratch and it's still doing it. 12 sp XT mech and SLX shifter. As far as I can tell the mech hanger is straight - it looks straight and I haven't crashed recently. Bike is an Orbea Occam if that makes a difference - when I got it I removed the groupset, rebuilt it and it was fine when I rebuilt it and for ages afterwards.
I don't know what's changed or how to fix it.
Any suggestions?
As far as I can tell the mech hanger is straight – it looks straight and I haven’t crashed recently.
I'd still get a hanger adjustment tool and check it. So often it's the hanger.
In no particular order.
Tension too high?- you need micro adjustments on 12sp Shimano, so go easy, it doesn't respond well to big turns of the cable adjuster
Mech hanger - it's critical on 12 speed, more than anything else.
jockey wheel float -make sure the top jockey wheel is free, there's not as much float on 12sp that there was on say 10 or 11 sp, but there does need to be some
Clutch - does it need a service, can you switch it off and does that improve things?
B tension set all OK?
How old's the cassette? is it just not playing nice with the new chain?
How old's the outer cable? Sometimes they just wear out and the inner sticks a bit in the bends.
Hiya,
As @nickc said tension too high I suspect. It's an easy mistake to make and critical from my own experiences too.
BR
JeZ
I'll have another go at re-tensioning it.
The mach is newish but it's behaving the same as the previous SLX mech (I had a spare XT mech detsined for another bike so have swapped them over) so I don't think the jockey wheel or clutch are the issue (clutch is off).
Cassette is also newish - I bent the biggest sprocket on the previous one through sheer power!
admission: I have never understood what the b-screw does and have never touched it on any bike!
I'll have a look into a mech hanger adjustment tool (or possibly just buy a new mech hanger).
Cable outer is original - 3 years old - so may also be worth looking at although I don't remember any issues sliding the inner through.
YouTube is your friend for things like setting up the B-screw
May as well swap the outer, what's the worst that can happen?
Orbea use/used cheap nasty outer as OEM, I changed mine to SP41 and it made the rear shifting immeasurably better and that was on a new bike. At 3 years old I imagine it's well past its best.
admission: I have never understood what the b-screw does and have never touched it on any bike!
B screw adjusts the distance of the derailleur from the sprockets. Or top jockey wheel, or something.
The amount of times I've spent a frustrating half hour trying to index gears and then remembered to check that screw is unbelievable.
Shifts ok going up, but not down
*tweak*
Shifts ok going down, but not up
*tweak*
Shifts ok in the middle of the cassette, but not in higher gears
*tweak*
Shifts ok at either end of the cassette, does weird things in the middle
*tweak*
Shifts ok going up, but not down
AAARRGH
Oh wait, let's check the B screw
*tweak*
*heavenly choir sings hallelujah* Glorious perfect shifting
Well sorry if this has turned out to be a non-event...
I've just popped it on the workstand to have a go at sorting it out and it's currently shifting up and down like a Shimano advert. The bike fixing pixies have been in my shed since the weekend.
How it works this evening when actually being ridden is another matter obviously. I've ordered some new outer anyway and will fit it when it arrives (and watch some b-screw videos in the interim).
What Cassette it it using?
I've managed to buy a duff Cassette recently a cheapo 'Bolany' which suffered this same sort issue with two completely different Mech/shifters. Fixed in both instances by fitting a different cassette having run through all the standard, fresh cables and hanger alignment, fixes first.
I eventually took a good look at the offending Cassette and I think the culprit was the second from top sprocket being a wee bit bent in the region of the shift gates (like ~0.3-0.5mm). What I think happened was that I was probably not needing to put so much tension into the cable for the down shift to go up the block, but coming the other way it was managing to cling onto the big sprocket until two clicks had been paid out, similarly.
Having played with it more the sheer bendiness of some of the sprockets was a definite issue, so I've shit-canned the Cassette, I don't trust it, I might give it a whirl on my Friction shifty winter bike just to see if it can be persuaded to work with that setup.
Oh and as ossify said B-screw makes a significant difference especially on wider range Cassettes, double check that before anything else.
Glad it's sorted, love it when the pixies come and fix your bike!
Can you send them my way as getting chainsuck currently.
I had similar. Ended up needing another link in the chain and a tweak of the b screw.
But I would absolutely buy a hanger alignment tool first. It will solve many shifting issues!
Agreed re chain length. Everything I thought I knew had to be binned when I actually read the chain installation instructions for Shimano 12.