Bicycle Mechanics - jockey pulley pops chain off when moving backwards

Hey all! I recently have begun to commute to work on my road bike. I love it and I am really happy with my decision, but it's been a little frustrating as far as maintenance goes. I am not at all mechanically inclined, but I am willing to learn and have thus far been ok. However, recently, I've had problems with my jockey pulley. I tried to search the forums, but I got completely overwhelmed. Also, I didn't see anything about chains slipping when the bike moves backwards. Here are the symptoms:

- jockey pulley cog/wheel shows some signs of stress (there's some wear and tear) - but it's NOT new.
- chain pops off ONLY when I move backwards
- shifting gears is loud and a bit crunchy
- I'm not exactly sure if the derailer lines up because I'm not sure what exactly it should look like when it is "lined up" - that probably means it's not
- won't stay in gear on hills (but I REALLY think that's a different problem; i.e., I need to tighten the shifter wheel doohickies - but it's worth mentioning)


Any ideas? This weekend I was going to take the chain off and clean it really good, check my cable tension, and make sure my shifters aren't on the loose side. I'm pretty intimidated about taking off my derailer, but I guess I gotta learn sometime... Any help would be *really* appreciated.

I'm sure others will add comments, but when I buy a used bike and the chain is gummed up from dried out lubricants and dirt, it exhibits all the symptoms you described. If you have not cleaned the chain, I would thoroughly clean it, off the bike, before making any adjustments or other changes. Also, check the chain to be sure it is not stretched and out of spec.

that is exactly the kind of answer I want to hear. that's what I'll do first thing.

Any recommendations for a good degreaser?

A picture would tell us a thousand words to go with yer description. Wouldnt be suprised if the der. hanger is bent. Might be helpful to know if it happens in all gear combos or just a few choice ones. As far as checking alignment without tools, site vertically fom directly behind the gears. The pulleys should be straight in relation to the cog the chain is riding on.

I would check your derailleur alignment. Correcting any mis-alignment requires a special tool, but you can
usually tell if your derailleur and/or hanger (that's the thing attached to the frame that your derailer bolts
to) is staight by looking at it from behind the bike. The pulley cage should hang straight down and be
parallel to the wheel both on the vertical and horizontal plane. If you see any mis-alignment you should
take your bike to a good shop. Most bike shops will charge around 15 dollars to align a bent hanger. If you
have a bolt-on aluminum hanger it would be better to replace it since aluminum does'nt bend very well.

Other thing to check (did the mistake once, so still clear in my mind): the back plate that holds the jockey pulleys onto the derailleur can be mounted upside down, i.e. the top pulley screwed in the hole intended for the bottom pulley, and vice-versa. Net effect is that the tab on the back plate that prevents the chain from moving off the bottom pulley is lost somewhere around the top one - giving exactly the symptoms you describe.

The derailleur alignment is the other potential culprit.