85 Delta 88.

OK how hard is it to do?

Should I buy the cable, or can I get away with just buying the "core" (Thinking is might be easier to install)

My speedo needle is jumping like crazy the faster I go. I heard a noise the other day (just thought because it was cold old) and ever since the speedo's been acting this way. It's really annoying

 

Not sure about the 85, but my 74 was a piece of cake.

Just pull the instrument panel forward, unhook old cable, remove panel at firewall bottom behind brake/gas pedal, disconnect cable at transmission and pull it through.

I replaced the whole cable. The core kits look like a PITA to me.