It might just be the cable. You can unhook it at the trans and spin it with an electric drill.
Have someone else look inside and see if the speedo is moving. Also see if the odometer is moving.
If nothing moves, unhook the speedo cable from the back of the speedo and see if the cable is turning.
If it is not, it's broken. I got a new cable from Napa.
If the cable does, and the odometer does, and the speedo doesn't, you need a new junk yard speedo.
If it all works, the problem is at the trans.
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OK, I'm over it. Where's the beer?