A lot of adapters have a grease fitting on them; Give it a shot to keep the gears lubed.
I always grease the cable when I'm doing PM or installing a new one.
One end has a collar and won't shove through the housing. That end is the one that goes into the speedometer head.
Take a handful of grease and shove the opposite cable end through the grease and into the housing from the speedo end.
Continue to shove the cable through the grease and into the housing. If you run into a snag, look to see if the cable housing is kinked where it goes through a securing clamp. If so, loosen the clamp and straighten out as much of the kink as you can. (resecure when done).
When you've got all but the last inch or two into the housing you may have to turn the cable in order to get it threaded into the speed drive on the trans/transfer case.
You're done when the speedo head end of the cable is flush with the end of the housing. Reconnect the housing to the speedo head (again, you may have to wiggle the housing to get the speedo end into the head) and you're finished.