Sram Eagle NX Rear Derailleur not reacting to cable tension

Question

Have had a SRAM NX Eagle rear derailleur (bike is a 1x) on my YT Jeffsy for about a year and a half. For about the first year, worked awesome, indexed the gears a few times and all was good. Last half a year its been a disaster.

I can't seem to get it shifting properly in either direction. I replaced the shifter cable AND housing (i know some people will just replace then shifter cable) and still having issues. What i've diagnosed is that it will shift up (or into high gears) and then the derailleur will get "stuck" when trying to shift back down to low gears. I can see the cable going slack and removing tension (i'll shift down ~3 gears) but the rear derailleur won't move from the highest gear. If i lightly move the rear derailleur back and forth it will overcome whatever is causing it to stick and then shift down into the intended 3 gears down all at once. Usually if i get up to 5 gears or so it will start shifting down without me touching it. Any ideas?

Answer 1

If you've replaced the cabling and you see it slackening off with no derailleur response, there must be some added resistance in the movement of the derailleur itself.

I suspect it is simply the pivots of the derailleur which need some lubrication. Either a spray of teflon lube on each pivot point or a drop of oil. Then, if you have the wheel off the ground, you can move the derailleur up and down the cassette while spinning the pedals, to exercise the pivots and free them up. Just mind your fingers.

Double check the guide pulley is far enough away from the cogs, something like 13mm from the largest cog for Eagle, so a decent gap.

I can't think what else would resist the return force of the derailleur spring, except a lack of spring tension... if you handle the mech and it still has finger-crushing spring tension then all good, but check the spring for any defects.

Answer 2

In my case the pivot screw for the swing-arm was fastened with too much torque. Lubrication of the moving joint of the swing-arm did not help. The hex-socket screw holding it together is accessible BETWEEN the swing-arm and the wheel. I had to find a small enough allen-key that could fit in in that space and loosen it one quarter-turn. Be careful to get your clockwise / anti-clockwise direction correct given you'll be standing on the other side of the swing-arm. Not sure why the factory fit it so tightly :(