Actually, a speedo cable problem usually results in the speedometer needle wildly going up and down.
But to lube the speedometer cable, you can pull the cable out of the housing from only one end or the other. If you can get under the car easily, it's easier to try that end first, just remove the lock bolt with a 10MM wrench and pull out the cable housing. Try to pull the cable out, if it is going to come out from out from that end it won't take much tugging with needle nose pliers.
If I remember correctly, it will probably come out from the top. Just take the hush panel from underneath the dash on the drivers side enough to reach up and push the instrument cluster out toward the steering wheel. Reach in and unscrew the cable housing with your thumb and forefinger. Then pull the cable out.
Once the cable is out lube it with speedometer cable lubricant from the auto supply store.