Red AXS dérailleur jumping/hunting problem

[tomato coupe]

Originally Posted by tootall

After the suggestion to test it on the bench, I took the chain off for a cleaning and tried the derailleur. It hunts worse! So either my derailleur is messed up, or that’s natural behavior when there’s no chain as the derailleur freaks out with no tension on it. See below. Pumps 7/8 times on one of the shifts. Would like to know if this is normal, but I don’t have any other AXS derailleurs laying around and no shops within an hour of here.

Your rear derailleur hasn't been wearing a helmet -- it appears to have a traumatic brain injury.

[m_sasso]

Looks like the position sensor is not reading properly.

Don't know what Sram uses to detect position, could be some type of light emitting diode. Try giving the derailleur a blast of compressed air, the sensor could have picked up some dust or dirt.

[KonaSS]

I think it is time to contact Sram on this one.

[sfo1]

I had a new eTap rear der go bad after a few months. I promptly received a new one.

Keep in mind that SRAM only takes warranty returns from authorized dealers (and unless you have a 'friendly' dealer, they will likely ask to see a receipt).

[oldpotatoe]

Originally Posted by Dave

The b gap isn't that critical, IMO. 12mm is a lot of gap, but it should only affect sprockets at the two extremes. I've run 10-36 cassettes with 33T capacity RDs and only 3mm of gap. Too much gap can cause the shifts to hesitate in the 10-11-12 range. It shouldn't affect the others a bit.

I always recommend trying a different RD. If the problem goes away, you may have a defective RD.

Pricey suggestion...Or warranty...maybe...

[Gman79]

Hope I'm not too late to the party here. I've been following this thread because I've been having almost the exact same issue with my Force AXS rd. I noticed within the past few months the rd is "jumping" when moving down the cassette into a smaller cog. Zero issues moving up the cassette.

I saw the comments concerning the B-Screw adjustment thinking if the motor is having over torque issues that could be the culprit. Now it must also be said that AXS has much more chain wrap on the cogs than any other mechanical groupset I use regularly. So much so I wonder if it's designed that way on purpose or if maybe it's the location of the rd hanger???

I did find a solution to the jumps by moving the B-screw all the way in then moving the derailleur thru the cassette while in the work stand. I'm not sure how this lines up with the official SRAM gap tool, but it worked. After I had everything indexed and the rd was moving without jumping I turned the B-Screw in 1/8 to 1/4 turns at a time until the jumping reappeared. When that happened I backed off 1/8 turn and so far things are much improved with shifting, noise, and jumping.

See the pictures below to see how my setup might assist your issues.




Bug Ring Big Cog combo. Yeah I know it looks like the chain is too short but there is still movement on the cage.



B-Srew setting



Big Ring Small Cog



Small Ring Big Cog

I also installed the firmware updates this afternoon before making any adjustments. Dunno if that helped or not.