Ok think im just doing something silly here, probably staring my right in the face but i just cant work it out. Basically all ive done is change from an slx medium cage rear mech to a deore xt rear mech and shifter. shifting up the gears is finebut when shifting down the chain catches the derailleur and stops it shifting down or just locks it all up.

I have a 40t cassette ring so my btension screw is wound quite the way in to allow for this… but even adjusting it still looks a bit close for comfort. Anyone else had this issue? or tell me what im doing wrong? 🙂 thanks in advance!

Is it a longer B tension screw (like you get with a Hope 40 t-rex) or a standard length one?

When you installed the XT mech, have you made sure the “stopper” (for want of a better description) that holds the mech against the mech hanger is flush?

Best way to check is, with the drivetrain still assembled & the chain in place, undo the mech bolt slightly; the tension will pull the stopper round to meet the mech hanger. If not, B tension screw.

Thanks guys, yep i checked the “stopper” infact when i checked that early on it did drop and sit flush and thought id got it but no such joy just been out there playing again. sets up nicely if i exclude the hope 40trex…

when thats included i can get it to work… sort of! it either catches slightly or isnt a smooth shift into or out of the 40T-rex

Wondering if chain length has anything to do with it? taking a link or 2 out may help? or just make things worse :/

Seems a bit extreme to take a file to the derailleur

Have you fitted the longer B tension screw when using the t-rex?
If not it would be a good place to start.

Is it a longer mech? Not unknown for the wrong size to be boxed up and labelled as something else? Is it a clutch also?

I’m running a shorted than perhaps ideal chain on my 1×10 42T one-up

I had to reverse my b tension screw as even with it wound all the way in, the cahe of my mech would catch on the 42T on the downshift.

It wasn’t the cable or chain catching but the cage itself.

fitted the longer b-tension. its defintly the medium cage and yes it has the clutch. Will go back to it 2moro and see how it goes with a fresh head and hopefully have more luck…. if not good bye t-rex

So turns out i went back out there and got it sorted in 10 minutes…. bit embarrasing really but the derailleur hanger was ever so slightly bent althought it didnt look it, but its all sorted now 🙂