Skipping new XT drivetrain

My new drivetrain is skipping in the smallest cog and nothing I’ve tried has worked. It’s 12 speed XT with M8100 derailleur, 10-51t cassette and can-m8100 chain. It’s on a Stumpjumper with the flex stays (not evo). Can you help?!

I’ve tried the following:

Staightened and aligned hanger

Checked wheel axle is tight

Setting limit screw by eye or by trial and error or just wound all the way out.

Chain has logos on the outside so is fitted with correct orientation. Quick link arrow in correct direction.

All cleaned and well oiled

B-tension wound out so chain is close to the cassette

Checked gear cable

Help!!

thought this was about postage….

sounds like you’ve done everything i would

to confirm, it’s a new chain and cassette? and its definitely chain skip and not the freewheel skipping?

it looks ok by eye? all in line?

got any pics of it just to idiot check?

did you fit it? if so sis you size the chain correctly?

also in bottom sprocket the cable should be a little slack – test by disconnecting the cable temporary

B- tension – use the alignment marks on the back of the derailleur cage, – only works properly if chain is correct length.

follow steps here:

https://si.shimano.com/en/dm/MARD001

of PDF here:

https://si.shimano.com/en/pdfs/dm/MARD001/DM-MARD001-05-ENG.pdf

Checked the 10T cog is on straight – the notches are wafer thin so it can be out of its slots and still look roughly right.

I’ll upload some photos later. Its only skipping in the smallest cog, so no issues in any other so I don’t think it’s the freehub (its a good condition DT240 hub).  The chain, sprocket and chainring are new. I’ve removed and refitted the cassette to check its on correctly.

B-tension wound out so chain is close to the cassette

Use the alignment marks on the back of the cage, not just ‘close’ by eye. MM or two in or out makes all the difference from my experience. Took me a lot of working out. The close ratio 10-45t cassette also does not play with the regular/common mid length mech either, you need to change the mech too for the shorter one to get clean shifting with the smaller casette – due to the B-tension as per above.

Chain length?

as above have a look at:

https://si.shimano.com/en/dm/MARD001

of PDF here:

https://si.shimano.com/en/pdfs/dm/MARD001/DM-MARD001-05-ENG.pdf

specific chain length:

https://si.shimano.com/en/dm/MARD001/Checking_the_chain_length

derailleur b setting

https://si.shimano.com/en/dm/MARD001/Adjusting_the_end_adjust_bolt

have to go through the steps on order and to start with don’t do by eye.

I had this exact problem earlier this year with a full new XT M8100 setup, it turned out to be chain length. It seems very sensitive to getting the exact number of links right.

also, if skipping only in smallest sprocket, check the lock ring is flush and not any little slivers  poking out – the crush washer can do this..

I had this exact problem earlier this year with a full new XT M8100 setup, it turned out to be chain length.

Same here. The ‘shimano way’ of setting chain length is not infallible, I think.

Is it a new chainring?

I checked the chain length and it’s actually two links too short, I’m not sure that would cause it to skip. 

I found the mech hanger was rotated slightly, so I adjusted it and checked everything again, including b-tension. 

Here are a couple of photos:

https://m.pinkbike.com/photo/25784026/

https://m.pinkbike.com/photo/25784024/

The rotated UDH will definitely be it, I got tripped up by this recently. It sounds so stupid, but coming from a world with fixed derailleur hangers you just don’t really think to expect it.

I had a Deore 11 speed that wouldn’t play the game on the smallest cog this year – replacing it with the old cog fixed it, so it may be a dodgy cog.

Abit of a while ago, but the fault was a recall issue on the dt 240 freehub. I ended up using a go pro pointed at the cassette to prove it wasn’t skipping and that the issue was the freehub!