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What's wrong with my shifting?!

by freetime101
Wed, May 26, 2021 20:33
11

Hi All,

I'm hoping somebody can help me here as I'm running out of ideas... I just cannot get my shifting right! Some time ago I leant the bike against a wall and it fell over onto the gear side... The shiftings not been right since!

For reference this is a 12 speed slx mountain bike and gets a lot more abuse than the road bike but the principle is the same...

Shifting up from the 1st (smallest) cog to the 2nd just clicks like a badly aligned gear, shifting again jumps up to 3 as expected. Shifting up the rest of the cassette works fine but then shifting down again from 8-7 doesn't work then shifting again skips down to 6...

I've fiddled endlessly with the cable adjustment, aligned the hanger with a park tool DAG3 (it was bent...), replaced the hanger with a brand new one, and now replaced the whole cable and outer... Shifting is better but still nowhere near what it was pre-drop...
Is there anything else I can try or is it time for a new derailleur?

TIA!

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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11 comments

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AfterPeak | 3 years ago
0 likes

Sounds like you have bent your derailleur hanger to me. You can either replace that or get the shop to straighten it for you

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freetime101 | 3 years ago
1 like

Well, I've fiddled and faffed and the shifting is now as good as it's gonna get... Maybe I'm expecting too much... Shifting on my road bikes has always been perfect (even with cheapy microshift) but I can never get my mtbs quite right...
I've thoroughly cleaned and degreased the whole chain, cassette and derailleur, then sprayed liberally with bike spray, wiped down then lubed the chain. You could eat your dinner off it now!

Shifting is pretty good throughout most of the casette, the cable is within 1/8 of a turn of being perfect (1/4 of a turn in either direction and shifting gets worse, damn these things are finicky!). However, it's still gears 1-2 that are being a pain!
Tightening the limit screw helped massively, thanks! 3/4 of a turn and now it shifts if I push the shifter just past the gear, almost to the point of shifting again. Tighten the limit screw any more and it won't shift back down.
All other gears shift on the click, its only 1-2 that needs an extra push, shifting back down comes with a clunk but at least the other 11 are fine!
Thanks again for the tips!

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kil0ran replied to freetime101 | 3 years ago
0 likes

Yeah, MTB is very precise. Those rear mechs are a masterpiece of compact engineering if you think about the range they typically have to handle. I've got Deore 5100 on mine - clutch, shadow, handles an 11-51T cassette with a frankly ridiculously bad chainline, gets covered in slop every ride, still works. 

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hbeevers | 3 years ago
1 like

Had a similar issue recently, turned out to be the anchor screw for the gear cable. There is a correct orientation that has a groove for the cable. It creates the correct "parallelogram" for the shifting without which it will skip gears.

Perhaps yours is something similar?

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Dave Dave | 3 years ago
0 likes

Sounds like the cable tension is off. Tighten it with the barrel adjuster.

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Dnnnnnn | 3 years ago
0 likes

For shifts at either end of the cassette, it could be that the limit screws need adjustment (esp. going from sprockets 1 to 2). Not clear why falling over would have affected their settings (assuming the hanger, mech, etc. are still/again in the proper positions) but tightening up the 'High' limit screw a little can help get the chain up to the next sprocket without having to overtension the cable (which would knock the other shifts out).

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freetime101 | 3 years ago
0 likes

Thanks for the replies, it's a Shimano SLX 12 speed (mtb) groupset. Shifting was perfect before I dropped it so unfortunatley it's something I've done. I've ridden it since the drop so it's possible I've added to the damage 2 

Cable and outer are brand new and move smoothly - though after taking it apart it seems there was nothing wrong with the original. 

Chain is fairly new and showing no signs of wear, could be a bent link I guess but the issue is with a specifc gear not the chain - I'll have a closer inspection. It's well lubed but admittedly a bit dirty - will give it a proper clean and try again. 

The shifting issue is the same whether the clutch is on or off. The mech moves freely end to end and once in the highest or lowest gear there is no rubbing and the chain doesn't try to jump off. Jockey wheels line up by eye - I'll have a closer look and report back. 

I'll start again and follow all suggestions this evening then report back. 

If I have bent the B axle or mech lower, how do I tell, and are these parts replacable or is it time for a whole new mech?

At least my road bike shifts perfectly... maybe it's just mtbs yes

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kil0ran replied to freetime101 | 3 years ago
0 likes

Pop the bike in a work stand, shift to the biggest cog, and back pedal the cranks slowly. Any kicking from the derailleur? Does it drop off the big cog?

Everything is serviceable on Shimano mechs but unfortunately they're such precise devices it's probably easier to buy a new one (assuming you can find stock) See https://si.shimano.com/pdfs/ev/EV-RD-M7100-4607.pdf

I can't see how this would be a possible cause, or how it would have happened from a drop, but maybe just pop the cassette off and re-seat everything on the freehub. Also makes it easier to check if there are any bent teeth on the cassette. As you're probably aware the cassette is split into three or four sections with spacers, maybe something is slightly out of alignment. 

I'm assuming you're running a thru-axle? Just ruling out anything to do with a damaged QR.

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kil0ran | 3 years ago
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Have you read the Shimano manual? The alignment and indexing steps for 12sp are a bit different to what you might have learnt on 10 or 11sp.

https://si.shimano.com/pdfs/dm/DM-MARD001-02-ENG.pdf

I'd go back to scratch and do the following:

1. Undo the cable from the mech

2. Check that the mech moves freely from limit to limit, and that the jockey wheels line up with the extremes of the cassette.

3. Click the cable out of the shifter as far as it will go

4. Connect cable to mech and do the initial tension setting 

5. Do the big cog limit alignment

6. Do the B-Screw (end screw) alignment - see pages 19 & 20 - this bit is the biggest change to the usual way of doing indexing/alignment

7. Switch the clutch off, move the chain to the middle of the cassette (5th smallest cog will do) and do the usual SIS indexing procedure with the barrel adjuster.

Wondering - and this is a long shot - but might you have bent the B-axle? The bit that connects the mech to the hanger? Or maybe it's not torqued up right.

 

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andystow | 3 years ago
0 likes

What groupset is it? If it's a BSO with a mech that just says "Shimano" on it, it's below even Tourney and SIS. I volunteer at a Co-op and find a large proportion just can't be made to shift properly at all. The best I can sometimes do is some gears get missed, but minimize the annoying ghost shifting.

If it's Tourney, Acera, or above, then other ideas:

  • Worn chain
  • Bent link on the chain
  • Does the mech move freely when the cable is disconnected and the wheel is off? The spring should snap it right to the outside.
  • Does the cable move smoothly in the housing all the way to the mech?
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Compact Corned Beef replied to andystow | 3 years ago
0 likes

Says SLX in the post. Misaligned jockey wheels if the mech lower is out of whack?

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