speedometer cable question

Lube it. Lithium or graphite is the current "go to" lube, but I have used regular general purpose grease in the past. Anything is better than nothing.
Pull the cable out of the sheath and coat it with grease. Then I use the needle attachment on my grease gun to pump as much grease into the sheath as I can from both ends. Rin the cable back through it a couple of times to distribute the lube. You can even attach a drill to the cable and spin it a little to make sure it's worked in.