Morris Minor Owners Club

I have a 3:9 diff which was a recon unit about 10 years ago according to the bills I have with the car. It's done about 5000 miles but is now getting very noisy at 50 and above. They seems to be a lot
Of play at the pinion end if you rotate the prop. Does anyone know how much backlash there should be on these diff's? Was wondering if it hasn't been set up properly

Thanks

Try tightening the pinion nut......