I got a new rear derailleur for my wife's bike after a stick turned the original one into a twisted mess of metal. The derailleur is a Shimano Acera, the cage is slightly longer than the original.
The rear cassette is a Shimano MegaRange with 7 cogs, the largest being 34T and quite a bit larger than 2nd.
When engaged on the second cog, the inner cage plate begins to rub on the largest cog. Getting into the largest cog isn't possible due to interference with the cage. I tightened down the B screw all the way, but there just isn't enough room.
The inner part of the cage on the original derailleur is a bit shorter than the upper jockey wheel. On the new one, the inner cage goes a bit beyond the jockey wheel.
Is there some adjust I'm missing or a different part I should have gotten? Worst case, could I cut the inner cage plate back a bit for clearance?
I found the tiny stamping on the old deraileur, its a RD-M340. The new on is a RD-M360. Both claim to handle a 34T rear.
With a little manual intervention, I can get the chain up on the top cog and it turns smoothly.