rear deraileurs and chain length

[jacksonpt]

I replaced my rear deraileur tonight... an 00 LX with an 03 LX, both long cage. When I got the new der bolted on, I noticed that my chain was waaaay to short. I could shift though all the cogs on my smallest ring no prob, but I couldn't get through them all on my middle ring. The big ring was a joke. I eyeballed everything, and the 2 der seem identical except for some aesthetics.

I have a spare chain, so the length isn't an issue, I just thought it was strange that there would be such a significant difference.

Is it normal for deraileurs to require different chain lengths? Or is this a signal that I might have done something wrong (even though it's shifting just fine)?

[Phatswalla]

There shouldn't be that big of a difference. Could you have grabbed the wrong chain to put back on?

[jacksonpt]

No... the other chain is in my pack in my truck. I was working on the bike in my kitchen. Maybe I'll throw the old der back on and do a quick compare.

[Repack]

Does the new derr have larger jockey wheels? That would do it. When did LX go 9S? The 9s stuff has larger pullies than the 8s stuff.