Deore m5100 B tension oddness

Hi all,

Installing a Shimano M5100 Deore 11 Spd mech on my daughters build and the B tension seems way off. the current gap between the 42T cassette and jockey wheel in the largest cog is ~40mm whereas it should be about 5-6mm according to various videos?? The B tension screw is wound all the way out so it isn’t currently touching the stopper, winding it in any more moves the user jockey further away from the cassette?

The moveable bit of the stopper on the Mech is currently between the B tension screw and the hanger, which is as I think it should be? I’m missing something, but unsure what at the moment.

Pics:

It doesn’t work on cassettes with such small cogs, it is for a 51t biggest cog

Ah, that’s annoying!

which version should I be looking for with a 42T cassette then?

Shimano Deore RD-M5120 Deore rear derailleur; 10/11-speed; Shadow+ SGS long cage

It will sort of work on smaller cassettes (I run a 46t ok, 42t might be pushing it). But what you do need is use a longer chain – enough to suit the 51t which isn’t actually there. Basically it uses the swing of the mech due to tensioning the chain to move the top jockey closer to the sprocket. If you look the top jockey wheel is a long way behind the top pivot, so the distance between jockey and cassette is massively changed by fore-aft cage angle.

As above – mine was even a bit tricky setting up on a 46t cassette. Needed a fair bit extra length than I originally used.

Ask me why my chain has two quick links in 😁

Hmmm, only have about 5 additional links spare but I’ll pop those in and see if it makes a difference.

She really needs another growth spurt to be comfortable on it anyways so not in a massive rush.

Cheers all.