Dumb question about adding clutch fluid... and low shift point

[atarijake]

Hello all, I'm definitely no mechanic... just trying to save a few bucks on some repair bills.

I went four wheeling over the weekend and now my 85 sierra doesn't shift the same, the sweet spot is like an inch off the floor. I tried adding more fluid but it doesn't act like it needs any? I unscrew the cap and there's this rubber plunge cap type thing that presses all the fluid into the line below the fill cap.

Can I add fluid and then pump the clutch to get it take more?

Are there any diagnostics I can do to determine if something needs to be replaced or maybe just adjusted?

Thanks!