45 day old SRAM rear derailleurs jumps gears have a 1x12 SRAM NX drivetrain on a fairly new full suspension MTB.
Been feeling great but yesterday it began skipping a gear when I shift. That is, if I start in 1 and click 4 times I wind up in 6th ring rather than the expected 5th.
The top and bottom limits seem ok because when I shift all the way through I do wind up on 12.
I know cables can stretch and I could bring in to a LBS but trying to avoid that.
I’m pretty handy with my bikes but derailleurs remain magic to me. Can anyone point me to a some easy advice or a great YouTube video.
When the shifting skips over a cog on the cassette gears, this is because the derailleur hanger (or less often, the derailleur cage) is misaligned. That is, the small sacrificial tab of aluminium which is between the frame and the derailleur proper. This can happen easily on any bike if it is mishandled or the mech strikes a rock etc., the age of the bike isn't a big factor.
The solution is a derailleur alignment gauge, which a shop will have and can check the alignment for you quickly and easily. You could buy one yourself but they aren't the most common home tool because they're pricey and hopefully you need one only rarely.
Cable stretch would affect each shift equally, the cable loses tension and it is sluggish to change into every gear, because the start point of the indexing is out and the error carries over to all shifts equally.
Your problem is that it skips past just one cog completely, part way up the cassette, which is an indication of misalignment. Playing with the cable tension could bring a little improvement, but if you are not proficient with indexing adjustments, the misalignment will cause you added frustration, even if you follow the instructions correctly. In this case it's well worth checking the hanger alignment at the same time as any indexing adjustments.