All gears shift smoothly, but won’t shift into 1st gear/large cog. Help? So I was tuning my newly acquired bike today and working with all 8 gears on the rear derailleur. I managed to properly set the high limit screw as well as cable tension so all gears shift smoothly from 2-7. However, when I try to shift to 1st gear, the derailleur won’t move and neither will the shifter. The cable tension is too tight. I also tried manually pushing the derailleur by hand and I can jusssssttttttt get it to shift into first, but it requires a lot of pressure. The only effect adjusting the low limit screw has had is that if it is too loose, it won’t shift from 3rd to 2nd. Tightening it anymore doesn’t shift it from 2nd to first. 

I briefly inspected for alignment and from eyeballing it things look OK, but I am not too sure. 

What are some things I can do or try and what should I be looking at if something needs fixing?

Thank you guys for your help.
From what you describe, it seems that pushing the derailleur inwards manually to get it onto the largest sprocket was tightening the shifter cable - that is suspicious, it should have loosened the cable.

First thing to do is disconnect the shift cable from the derailleur and check three things:


The derailleur will swing through its full range
The shifter will click through all gears.
The cable travels freely. You should be able to get hold of the shifter and derailleur ends of the cable and pull it back and forth.


If anything is hanging up or jamming, that is where you need to look for problems. I'd also check the shifter cable routing and make sure there are no cable and housing are where they should be and there are no kinks.