Trigger Gear set up gears wont index.

[markharry66]

I have an old bh bike. Neglected its hybrid with shimano gear set up. I cant seem to get the gears to index. Never had a problem with indexing gears in the past. Gears will index for first four on all three cogs going from top to bottom. But keep skipping gears straight down to the bottom its eight speed the middle gears will not index at all.
Where the chain feeds through not sure what that part is called two cogs at one point in the top cog of the triple it was hitting spokes. In bottom cog in lower gears chain is rubbing is this time for a new derailer.

 

[mjr]

Probably new derailleur time. It sounds like the spring that pushess it away from the rear cogs has failed. The part with two small wheels is the jockey wheels, I think. Some derailleurs have a screw on the back to adjust B tension but I'm not sure that's the problem. I'd take it apart, clean it in case there's muck blocking its expansion, reassemble, then replace if it persists.

 

[raleighnut]

If you decide to get a new derailleur get the shop to check hanger alignment, only takes 5 minutes.