ammarolli

I got new 9 speed shimano altus rear derailleur in the beginning of May at one of my LBS.
I went to both the LBS who put the derailleur on the bike and the bike dealer.
I still have this problem that the chain is at least slipping off the lower jockey wheel in gears that I should not be using 1x8 and 1x9. You can clearly see this problem when backpedaling but only noticing that right now that I see this while backpedaling.

The LBS who put the derailleur on the bike told me that the derailleur was little bent but they told me that they manage to get it straight. They also told me that the derailleur hanger was bent and I needed a new one. I went to the bike dealer to get them to change the derailleur hanger but they mange to bent it back.
I went to the dealer today cause of this problem and they adjusted the derailleur and I still have this problem.

Anyone got any idea what could be the problem?

corrado33

If it's new then why is it bent? Have you wrecked a bunch?

There's no reason to be in 1-8 and 1-9. I wouldn't care if my derailleur didn't work in those gears. Shifting often gets finicky if you cross chain that much anyway.

ammarolli

The bike fell down on the drivetrain side once while storing the bike outside of a shop I was visiting but that was in May. I also notice that the paint on the bike on the drivetrain side got damage few days ago but I have don't know how that happen. I usually don't cross train and kind of only use 1x in the winter time.

corrado33

Well, I would look at the bent(?) derailleur and bent(?) derailleur hanger first. Those are likely the culprits. I would say that possibly the jockey wheels (plastic) are worn down, but considering this derailleur was new in may, I doubt that.

ammarolli

The guy who adjusted the gears on the bike today checked weather the hanger was bent but did not say anything about it being off. The derailleur might be though bent.