I have a 1986 VN750 Vulcan

The Odometer (distance/miles traveled) works but I can't tell how fast I am going. I have a brand new speedo cable and a brand new speedo sending unit (down by the front tire). The cable is securely connected on both ends.
The cable is also sufficiently greased but I can't figure out where the problem is

Here is an update, I took some compressed air and blew it into the hole where the speedo cable connects to gauge. now it registers a speed but the needle climbs very slowly. So by the time that i have reached 25mph the needle only says 10mph. While working on the bike, I noticed that the speedo gauge is cracked on the inside of the crome bucket, could this be the root of my speed problem??

sounds like the speedo unit itself took damage. the reason i say this is cause the odometer still works which to my knowledge gets its info from that input cable that you checked.

Are you the original owner. if its cracked inside it may have been dropped then "fixed" and became a time bomb till it quit working correctly. try e-bay or a kawa dealer for the part