I’ve just fitted a new chain & cassette, swopping my old 11-42 for 11-46 cassette.
The top of the cage on the rear mech now fouls on the large sprocket & eventually the large sprocket gets stuck between the cage & top pulley so it won’t shift back down.

Shimano info suggests its compatable;
http://productinfo.shimano.com/#/spec/2.4/MTB/Rear%20Derailleur?q=RD-M8000&popup=1&from=ti

Anyone had this issue & cured it? Tried the B tension screw fully in without success.

I’m running that set up with a 32 ring up front. Sounds stupid but have you connected the cable yet? Mine fowled when pushing the mech to set the limits but didn’t fork when under cable tension if that makes sense?! B screw was mostly wound in but not fully

Fully compatible, thats what i’m running on my bike at the moment.

should work perfectly, you’ve done something wrong.

What frame? There have been issues when the mech hanger has the incorrect alignment, holding the mech at the wrong angle.

Its a Turner Czar. The mech hanger & receiving thread for the through axle are all one casting.

I took the wheel out, removed the 11-42 cassette, installed the 11-46, replaced the wheel in the frame, installed the new chain, slightly adjusted cable tension for quiet gears, but the mech clashes with the 46t sprocket.
Tried B tension screw in a variety of positions with no effect.

32t Oval chainring up front.

Tried B tension screw in a variety of positions with no effect.

No effect at all? As in mech not moving?

Should just have needed a bit if B tension if all you did was replace cassette. Sure you don’t just need to keep going, it can need a few turns…

I had it fully in but never saw it move at all while turning.

Is your chain short enough?

I’ve just come in from working on almost the same setup.

When roughly setting screws without a chain or cable, I noticed that the rotation angle of the cage (the dangly bit that tensions the chain) made a big difference to the clearance between top jockey and 46t sprocket. Pull the cage forward more (e.g shorter chain) increased the clearance.

B tension and limit screws are also in different locations / order compared to older mechs (i.e are you turning the correct screw).

I had it fully in but never saw it move at all while turning.

Something is wrong there then, you should see the mech visibly moving. I don’t want to insult your intelligence but are you sure you were adjusting the correct one and not a limit screw?

I don’t want to insult your intelligence but are you sure you were adjusting the correct one and not a limit screw?

Now look here!! I’ve built dozens of bikes over the years (but not in the last year or two). And I was rushing to do it while the wife was out with her mother & sister when I should have been preparing the ground for the 70 sq.m of turf that’s coming in the morning.

Of course I was turning the bl@@dy limit screw!!!!!
…….chuffin new style rear mechs!

THANKYOU!!! 😳

Haha! Glad you got to the bottom of it, happy shifting!