peugeot 206 1.1 petrol 2001 speedo not working common problem help needed?

Hi guys i got told to come here for help as my speedo is not working, I have replaced the speedo sensor off the gearbox side from another car in the breakers yard and it still is not working.
I have also ran a cordless drill to the shaft of the sensor with the wired plug conected and had it spinning to see if the speedo works that way, and it sure does go up and down at high and low drill speed.
When i enter the speedo sensor wheel into the box start the car in gear on the ramp i can feel it turning in my fingers.
What the hell can it be now, clocks working, sensor spinning, wires ok as its getting a pulse.
The only possible thing i can think that it can be now is the cog in the gearbox side is worn and when its connected up under pressue its slipping which i can not feel.
Has anyone on this site or anywhere else had this problem and had it fixed or have any info.