I have a 2021 nukeproof reactor with full SLX drivetrain. I am struggling to get it to shift smoothly and have run out if ideas. The bike shifts from large to small cogs great but when shifting to larger cogs it struggles in a few places (5th to 4th largest, 3rd to 2nd largest and 2nd to 1st largest). The chain will skip a bit until it finds the right tooth on the cog to allow it to shift (tick,tick,tick, tick shift) unless I get lucky and shift at the exact point the right part of the cog comes round. The only thing that seems to help is reducing the chain tension but then I can't shift properly in the smaller cogs.
This would suggest to me that the hanger is bent but I have checked it and it is perfectly straight, the derailleur cage appears not to be bent also. I have also played around with every possible position for the b screw and have not been able to find a sweet spot. I have set up the RD from scratch using the Shimano manual and still it won't shift smooth. The chain was 2 links longer than Shimano recommends but shortening it has not helped.
I went back to my LBS as it is only about 5 weeks old and done 50 miles and was told that this is normal. This doesn't seem right to me and must be causing unecessary ware on the cassette.
Any suggestions or am I expecting too much from a 12 speed RD.
Cheers
It's definitely not normal and is more than likely either poor routing or poor set up, 1/4 or 1/8th turn more tension on the barrel adjuster should sort it as that will help pull the mech up against the spring to shift from small to next largest.
You say you've checked the hanger and it is perfectly straight, is it perfectly aligned?
FWIW my 12 speed XTR is absolutely flawless and has been for over a year and a couple of thousand km's
Is the mech straight? - yes
Is the mech aligned? (1st and 12th does the mech sit directly below the teeth of the cassette - use H/L screws to set limit of movement) and using the B screw to set distance/ allow movement across the cassette.
Adjust the gears by starting in the middle of your range.
Still jumping? Is the chain line correct? (A spacer missing or not present on the bottom bracket, front crank shonky).
The derailleur should have a mark on the side of the derailleur cage (facing the wheel) that you use to set the b tension.
I have found 12 speed to be more sensitive than 11 speed and have had various problems. Sometimes only one single click on the barrel adjuster will do, and they're sensitive to small alignment issues. I also think the bigger gaps between gears generally make them a bit more clunky. B tension can seem like a dark art too. In your situation I'd set everything per instructions and start with adjusting indexing just one click at a time, while riding. I find if I set it in the stand it still needs a tweak to work right in actual use. I've recently fitted new cassette and mech and it has taken me a similar mileage to get it anywhere near.
When you say you've checked your hanger is straight, is that with an alignment tool? One of those can make the difference.
Have you tried unscrewing the cable screw so its slack and dialling in the limits? Eg turn the limit screw as you turn the cranks until it’s rubbing and loud then back it off just enough to stop that. 12 speed has less tolerance so if it’s out the chain can try to climb a gear etc.
I've got a XT 12 speed and just one gear that skips (7th), how is this possible when the rest work right? I can't see any damage to that cog.
Mugboo
Full MemberI’ve got a XT 12 speed and just one gear that skips (7th), how is this possible when the rest work right? I can’t see any damage to that cog.
I'm tearing my hair out on a similar issue, 9 cogs are just 'ok' but shifting between the largest 3 is all over the place. Think the hanger is ok but have a spare on the way to compare against
Yeah, I have one cog in the middle of the cassette that is either slow to move up to, or slow to drop down from, depending on cable tension. Hanger has been checked recently. I could try fiddling with b-screw, but normally end up making things worse!
Went out on my old 9-speed last week. Shifts beautifully...
I would check to make sure that the cable is correctly routed onto the mech itself. If you get it the wrong way round you can see the symptoms you describe..
I've got an XT 12 speed and it needed to be set up exactly as described in the manual.
Went out on my old 9-speed last week. Shifts beautifully…
9 speed b-tension guide: "Does the mech crash into the gears? Yes - move it away, No - go riding"
I would check to make sure that the cable is correctly routed onto the mech itself. If you get it the wrong way round you can see the symptoms you describe..
I had the exact same issue on my 12 speed SLX groupset and as above i had the cable routed wrongly into the rear mech, once routed the correct way the shifting was spot on
I’ve got a XT 12 speed and just one gear that skips (7th), how is this possible when the rest work right? I can’t see any damage to that cog.
I had that on my SRAM Force AXS 12sp drivechain. Turned out the derailleur was a bit loose in the hanger. I was convinced I'd managed to knacker the cassette. It was perfect in every cog except one.
Thanks for all the suggestions.
High and low limits have been set as recommended by Shimano.
B screw aligned with line on the back of derailleur. I have also made micro adjustments either side of the line.
Chain line looks good. Spacers on BB are correct.
Cable attached to derailleur as per Shimano instructions.
Hanger straightened with alignment tool. It is a homemade one but has zero play and I can't see why it wouldn't give accurate results.
Adding tension doesn't help. If anything it makes it worse. The guide pulley is far enough over the chain is just catching on teeth that it shouldn't. Removing tension helps but then the shifting in the smaller cogs is all buggered.
I have also checked the spacers in the cassette are in the right places.
I have a new mech hanger arriving today so will go back to square one to see if I can get it working better.
Sounds like your fight is exactly the same as mine Goopy. Only difference is that my cassette and chainset are Deore - which shouldn't make any difference. I've also got a new hanger on the way, so if I find a magic bullet I'll report back
Just to confirm I’m not losing it - there’s not an issue here (bar lack of wheel/cassette)?
As Imgur linking no longer seems to work: https://imgur.com/a/VLYXx7K
That's what mine looks like..so maybe we're both wrong 😁
It's not the clutch is it??
Happens with both the clutch on and off
Can you get a video of it shifting?
p.15. Assuming the tense-looking cable in your pic is the cable entering the mech...I'd say it's the wrong way round. My XTR rear is fine and has the cable entering as per the manual.
Odd that there's room for error though really - Shimano usually make this stuff really obvious with little or no need to RTFM.
I don't think it is the wrong way round. In the OP's pic the mech is at its slackest with zero tension.
I don’t think it is the wrong way round. In the OP’s pic the mech is at its slackest with zero tension.
Well, yeah, hard to tell. Worth a check though since there's some doubt.
I think your cables routed the wrong way round. I had exactly the same issues you describe after I'd changed a cable.. took me ages to diagnose it.
12 speed is a bit weird in so much as when its routed correctly it looks wrong.
Try reversing that routing and see if it improves..
Oh and its REALLY sensitive to the end stops being set correctly
Worth a check though since there’s some doubt.
Yeah it is deffo worth checking.
Actually I was assuming the top bit came from the cable housing.
OP if the top part of the cable in your pic is the bit with the cable end cap then it is the wrong way round.
OP if the top part of the cable in your pic is the bit with the cable end cap then it is the wrong way round.
Assuming we’re talking about my pic, the cable is coming in from the top and the bottom is the loose end. So correct per the manual, which is one of things making it particularly infuriating
So the bit that looks a bit loose is actually the bit from the cable housing/end stop? if so that is the right way round.
I'd go back and double check the limits top and bottom in that case, also check the mech is tight on the hanger, other than that, no idea. My 12 speed shifts fine in every gear. (well it did, cables a bit knackered now, but its definitely not normal)
So the bit that looks a bit loose is actually the bit from the cable housing/end stop? if so that is the right way round.
Yup
Limits checked, b-tension checked, mech has been off the hanger. All very odd
I just finished fitting a new hanger and setting the deraileur exactly as described in the Shimano dealers manual. I still get the same result. Here's a video. I'm I just expecting too much or should I be demanding that my LBS do more to try and resolve it
http://imgur.com/gallery/bIOxOTP
I’d be ok with that. Probably just because this is what mine is like by comparison
https://imgur.com/gallery/8fIWnMH
No idea why it’s not uploading with sound 🙄 You can see how ****y things get in the three largest cogs anyway
OP - my XT is the same as that. I think that is as good as you are going to get. I’ll video mine tomorrow when I can get it on the stand….
@mashr - yours deffo needs some tweaking….
Agreed. New hanger will be here tomorrow, hopefully it makes some kind of difference. What the video (without sound if nobody is getting it) doesn’t really show it that the bottom cogs are “push and hold” to move up, whereas the top ones are over shifting - you can see it basically jump straight past the second biggest cog.
It’s a little better than that now (that was last night) but still crap
Yeah I can see it jumping on the biggest cogs. I think you need to start from scratch with the barrel adjuster nearly all the way out (clockwise) and then adjust the slack out of the cable again, make sure not to move the derailleur at all while taking out the slack. If in doubt leave it slacker rather than tighter….. then follow the Shimano guide for SIS adjustment exactly.
I am assuming the cassette has the spacers in correctly and it’s a Shimano chain…..?
Is this your first Shimano 12 speed setup? It could be your shifting technique. I had similar issues on my new SLX setup until I realised that I was still being a bit gentle on the pedals and controls while shifting as you have always had to be on 11/10/9 speed. The new 12 speed is designed to shift smoothly under load so is optimised for that scenario, the ramps and chain don't seem to be as happy when shifting when soft-loaded. If I'm a bit more positive on the shifter and keep the power on the pedals it shifts a fair amount easier and smoother. It's a very subtle but definite change I've found.
Oh and is your chain a Shimano one and the correct way round? The 12 speed chains are now directional.
Oh and is your chain a Shimano one and the correct way round? The 12 speed chains are now directional.
That’s a good point. Your chain looks like it either on the wrong way round or it’s not a Shimano one. The writing should be on the outside for a Shimano chain.
At that point the chain was back to front (not my doing, honest!). Switching it round made naff-all difference.
All the other stuff you suggest about starting from scratch has been done several times over now, but no doubt I’ll do it several more times tomorrow
It’s not shifting technique, it’s dog-shit in the workstand without even having to shift anywhere
Personally, I think 12 speed is just a step too far for reliable use in grubby conditions.
I have the issues as above with mine, just generally crappy shifting and endless clicking and light grinding when less than spotlessly clean.
By contrast, the 11 speed XX1 stuff, 10 speed Microshift Advent and 9 speed stuff I have on other bikes is fuss free. Two bikes with SRAM 11 have been dead reliable for years with easy setup and tweaking when required.
The ultimate is the 10 speed XTR now on my turbo bike, so slick...
Have you checked the chain length? It’s different to the old chainring + largest sprocket + two links. I found that if you can’t quite get the length right the b screw can compensate pretty well, but chain length is is better to fix.
I would say I’ve found 12s slx pretty easy to get shifting well, so may have got lucky. Done three now. *Keeping* it shifting well when the main pivot seizes up, that’s much harder.
Chain was too long on arrival - had hopes pinned that was going to be the instant fix!
Cable housing may have couple of strands sticking out or it might be broken near adjusters or derailleurs, even if it is quite new.
Always annoying to find it as final check.
Bloody mech hanger!!!
Could see a tiny difference between old and new. Haven’t fine tuned everything yet but bike is actually rideable now
🙄👍😎 Nice - glad you've resolved it.
🙄👍😎 Nice – glad you’ve resolved it.
+1
I went through similar last year. I variously cleaned, lubed, set the various mech settings, straightened hanger, replaced cables, replaced chain, replaced freehub bearings. Various of these changes seemed to make a small improvement, so I thought I'd cracked it. Multiple times. Eventually I replaced the not visibly bent mech. That did seem to solve it but to me this all just underlines how bloody sensitive 12 speed is. I'm now another replacement down the line on most of these bits and I still quite honestly wouldn't say the shifting is as I'd like it to be.
on a similar note, i changed from SRAM GX 12 speed mechanical to AXS in the Spring and had same issue. I could't sort it, neither could LBS. As a last resort I put on a new hanger and it was perfect.... Seems that even a tiny bit of hanger distortion can throw 12 speed shifting
'B' screw.....
Last time I had a head scratcher indexing niggle I changed my cables and made the outer a touch longer at the rear mech and fixed it, whether it was the new cables or a gentler bend entering the mech I'll never know.
- fixed chain length
- new inner cable
- new outer cable
- correct chain direction
- check cable routing
- new mech hanger
- setup as per manual x 34
Seemingly (just about) ‘ok’ in the stand, total crap out on the trails.
Bought a hanger alignment tool, was a little out so sorted that. Still not a massive improvement. Only things left to change are chain (no indication of issues) or the mech itself….. so I took no prisoners with the latter. After 5-10mins of hauling and checking I now have 12 actual fully functional gears! Definitely still a very sensitive setup, but 1 click up or down now does exactly as it should. That was definitely harder work than it should’ve been!