Okay I'm stymied.

I am doing some work on my touring bike that involved removing my shimano 8 speed indexed bar end shifters. When I put everything back together I can't shift onto the lowest gears - biggest cogs- on my cassette. I tried setting up my shifting from scratch, loosening and re-tightening the shifter cable, checking the limit stops on the derailleur, but it seems like the shifter isn't pulling enough cable to shift onto the big sprocket, even in friction mode. If I push the derailleur with my hand I can easily get it to shift onto the biggest cogs. I thought I might have re assembled the shifter wrong, but as far as I can tell there is only one way it can go back together. But maybe I am wrong.

This is driving me crazy as it shifted perfectly before I started working on it. (I know, I know, if it ain't broke...)

Any help would be much appreciated.