John Deere 830 (1974) won't move

My JD 830 will not move when gear is engage(forward or reverse), however if I engage the differential lock the tractor will move in forward or reverse. Can someone diagnose this particular problem?
Thanks
Carri

Sounds like a broken axle. Normally, only 1 wheel pulls, which allows different speeds of the rear tires during a turn. The differential lock locks both sides together, where they both turn the same speed & power, this is what gets you out of trouble when 1 side starts to spin in the mud.
Good luck with it.

Good guess Redneck.

Tear into it now before you contaminate bearings with metal filings. Should have a clip or a pinch bolt keeping it from sliding out.