I’ve got a 10spd X9 rear mech on my bike and today for the first time I was having issues shifting off through biggest two cogs at the back, a 40t expander and the normal 36t one.

It’s like the mech was jamming, a quick bounce of the rear wheel and down the mech & chain came.

It was alright in smallest to the 3rd biggest both up & down.

Bike has done 350km and never had this issue before.

Any clues?

Downshifting? Could be a sticky cable or even a dodgy shifter rather than the mech

The shifter is releasing ok, I’ll try a new cable. Seems strange it’s knackered about such a short time on a full inner internally routed system

Bit of chain growth then or even a slightly bent hanger? I would tick off the usual suspects first.

One thing I found with SRAM mechs was that they were sensitive to cable routing but I assume you haven’t changed that?

Guide pulley sticking on the sprocket? Add some b-tension for more clearance and see if that fixes it before throwing money at it?

Check inner hasn’t frayed where it enters/rubs the rear mechs cable guide, inners have a habit of snapping here, especially when used in dirty conditions.

Cheers chaps, I shall investigate.

Never had this issue with a shimano machine and this is my first sram drive train in eons