Speedometer

[57halfton]

The speedometer in my 57 Chevy pickup hasn't worked for sometime now, i have checked the cable and the speedo gear in the trans and everything looked ok so today I swapped out the speedo cluster for another one I had.
After I got everything back together I drove it around the block and still nothing worked so I took the cable off of trans and put a drill motor on it and the speedo went up too about 45 mph, I then took the speedo gear out of the trans and it looked ok so I put everything back together again and drove around the block again this time the odometer seams to be working right but the speedo is reading slow, like 8 mph and 30 mph according to a sign that tells you how fast you are going when you go past it.
Anyone got any ideas? All the running gear (trans, speedo gear, and the rearend gear raito is all the same as it was before the old speedometer quit working.
Thanks , Gene