First things I'd check:

• Chain length
• B-tension

=sParty

 

Length is perfect; Need to check B tension. Would that explain why it shifted perfectly with clutch off?

Check that the chain has Shimano writing towards the outside of the bike too.

why indeed it does

 

Check that the chain has Shimano writing towards the outside of the bike too.

 

I can't speak to 12 speed but on my 11s shimano I had a very similar issue. This was after going from an 11-46 to 11-42. A small adjustment of the b screw to bring the derailleur closer to the cassette made the shifting work flawlessly with the clutch on. As a bonus it also quieted down the chain slap a bit. Definitely worth tinkering around with if you haven't yet.

 

Thank you both, will mess with that tonight

 

Is the clutch sticky? A common issue with Shimano derailleurs. They are easy to lubricate and adjust.

 

I too had sluggish shifting from the biggest cogs to smaller cogs with my 1x12 drivetrain (SLX shifter and rear derailleur, deore 10-51 cassette. Like other have mentioned, b-tension is critical with this setup. I found that adjusting the b-tension per Shimano's guidelines (longest tooth on the biggest cog even with the line etched on the derailleur) left the upper jockey wheel much too far away from the cassette for crisp shifting.

I now adjust the b-tension using Kyle Warner's setup guide (see link). In a nutshell, I first remove the droop from the chain when it is in the biggest gear (smallest cog) by tightening the b-tension bolt progressively. I then give it just a little more tightness to make sure the chain doesn't bounce excessively in the smallest cogs. Lastly, I check to make sure there is adequate clearance between the chain/upper jockey wheel and largest cassette cog teeth. This results in the cassette teeth a fair bit lower than the line etched on the derailleur...and much better shifting.

 

I too had sluggish shifting from the biggest cogs to smaller cogs with my 1x12 drivetrain (SLX shifter and rear derailleur, deore 10-51 cassette. Like other have mentioned, b-tension is critical with this setup. I found that adjusting the b-tension per Shimano's guidelines (longest tooth on the biggest cog even with the line etched on the derailleur) left the upper jockey wheel much too far away from the cassette for crisp shifting.

I now adjust the b-tension using Kyle Warner's setup guide (see link). In a nutshell, I first remove the droop from the chain when it is in the biggest gear (smallest cog) by tightening the b-tension bolt progressively. I then give it just a little more tightness to make sure the chain doesn't bounce excessively in the smallest cogs. Lastly, I check to make sure there is adequate clearance between the chain/upper jockey wheel and largest cassette cog teeth. This results in the cassette teeth a fair bit lower than the line etched on the derailleur...and much better shifting.

I’ll check this out, thanks

Sounds like you need to service the clutch. How is the movement of the cage when you press it with your hand? It should be smooth and not jerky with the clutch on. There are a lot of videos how to do it, just make sure that you don't lubricate the roller bearings inside the clutch, they should be dry. Take a picture and be careful to assemble it correctly.

If/when the b tension doesn't fix this will be next!

 

Sounds like you need to service the clutch. How is the movement of the cage when you press it with your hand? It should be smooth and not jerky with the clutch on. There are a lot of videos how to do it, just make sure that you don't lubricate the roller bearings inside the clutch, they should be dry. Take a picture and be careful to assemble it correctly.

 

I had this happen with my bike, also with an SLX transmission.

It was a misaligned derailleur hanger. Bent it the correct way, and the issue went away.

The problem had nothing to do with the clutch. If the hanger is only slightly out of alignment, the clutch just makes it a bit harder to shift because of the added tension, and that is enough to cause the issue.

 

Know this might sound useless but, have you tried adjusting the tension of the clutch? Too tight and it starts to shift badly

 

^^ Bingo!

I found Shimano clutch is over-tensioned from the factory. My SLX and two XT clutches were on the stiffer side and it was also not very smooth to rotate the cage with the clutch engaged. I backed off the tension screw a 1/2 turn and tried it on the street and it was shifting night and day better. One of them I had to back off the tension around 3/4 turn and now they all shift smoothly with the clutch engaged. I believe the clutch tension (NOT to be confused with the clutch's tension screw) is supposed to be set around 3-4Nm. You can also add a dab of grease to clutch at the pinch spring (NOT the inner part of the clutch) so that the cage operates smoothly with the clutch engaged.

 

Id try using a tiny bit of grease around the outer clutch barrel, between the barrel and the tension band that surrounds it, had some mad issues with a new XT clutch sticking

 

Agree that that's a possibility too.

Shimano Clutches require servicing them to keep them working well. Otherwise they start to stick.

 

Check the clutch band for grease. Dang it, I'm late for the party again.

 

Check if you derailleur moves at all when you downshift from the biggest cog.

If it jams in one position, when there are several possibilities:

1. Old and rusty cable and housing. The derailleur spring is too soft to overcome high friction and pull the cable back from the shifter. Replace the cable and the housing.

2. Dry parallelogram pivots (my case was that). If you ride in very wet conditions or spray your bike with soap or degreaser, the grease from the pivots washes away and the derailleur becomes sticky. The upshifting is ok, because you pull it by the shifter, but downshifting suffers from the friction. Drop some chain lube in the pivots and move the derailleur by hand to distribute it. Strangely, but somehow the clutch affects it. My derailleur was more eager to jam with the clutch on. If it is the case, also clean and regrease the cage axle.

3. Rusty or worn out clutch. Normally, it should not affect downshifting, but in the worst case it can. Try cleaning and greasing it. If it does not help, replace it. Shimano part no. is Y3GF98040.

Here is a good disassembly guide: NSMB.com - Shimano Derailleur Clutch Service

 

In between dad duty, I've done some moderate testing on this - it seems to be option 2 here. The derailleur moves fine and smoothly with clutch on when I push on it, so it didn't seem to be the clutch. But adjusting the B-Tension was so tight that I started to lube the pivots. This immediately changed the shifting performance with the clutch on, specifically from the largest cog to the next 2-3.

I'm not ruling out another variable, and will continue testing but this one simple tweak immediately got things back to like new. Great suggestion!

 

Last bike I had , had the same problem. I even replaced the shifter cable and housing too. I spray lube the linkage. Gone

 

I had the same issue with a deore 12s. I re lubed clutch and played with b screw which didnt help. What ended up being the fix for me was making the L screw a little tighter - even though it had seemed perfect already. Hope this helps

 

Oh... check another thing: make sure that the cable is clean and slides well in the housing. I once had a problem where the derailleur would upshift really slowly while on the bigger cogs. I finally discovered that a portion of the cable didn't slide properly although it was apparently clean.

I sprayed a bit of silicone oil on it, cleaned with a rag, and it kept working as usual.

 

This was just replaced and slid very well in the housing, so it's at the bottom of my list to check...for now. Thanks!

 

Bike Radar also tested the Shimano Deore M6100 groupset and they too concluded that setting up the b-tension according to Shimano's recommendation netted less than optimal results (see the Installation and Setup section of this article). They also list further ways to improve shifting further down in the article.

As for b-tension affecting chain retention, I did not see a correlation. I adjust the low gear limit screw by putting the chain on the lowest gear (biggest cog) and tighten the limit screw a half turn at a time until it starts making noise. I then loosen the limit screw a quarter turn at a time until the noise stops. Park Tool recommends setting the low gear limit screw this way and says this gives the most protection against chain drop into the spokes. Using this technique results in the upper pulley not directly under the lowest cog but just a tiny bit further towards the next cog.

 

Bike Radar also tested the Shimano Deore M6100 groupset and they too concluded that setting up the b-tension according to Shimano's recommendation netted less than optimal results (see the Installation and Setup section of this article). They also list further ways to improve shifting further down in the article.

As for b-tension affecting chain retention, I did not see a correlation. I adjust the low gear limit screw by putting the chain on the lowest gear (biggest cog) and tighten the limit screw a half turn at a time until it starts making noise. I then loosen the limit screw a quarter turn at a time until the noise stops. Park Tool recommends setting the low gear limit screw this way and says this gives the most protection against chain drop into the spokes. Using this technique results in the upper pulley not directly under the lowest cog but just a tiny bit further towards the next cog.

Thanks for this - I did a race last weekend so kept it on Shimano's recs (after re-setting low limit screw). No chain drops and pretty solid shifting throughout. I will try out this way vs. Shimano's recs as well.

 

Sorry forgot to include the Bike Radar article.

Shimano Deore M6100 groupset review

Shimano’s latest 12-speed M6100 Deore drivetrain represents incredible performance for the cash

www.bikeradar.com

 

I'm back to the stock B screw position on my Shimano XT. I agree closing the gap does make for some crisper shifting, but I can see rubbing marks on the jockey wheel and cage, so the derailleur is definitely contacting the cassette on larger hits. There is a reason Shimano has it set where they do.