The circle on the 1982 JD 570A wouldn’t turn smoothly and locked up where it wouldn't move and had to back it up to free it. We opened the circle drive and found the vertical shaft to be worn so bad the large gear would tip up and cause the worm gear to bind. The picture don’t show it well however the housing was worn egg shaped.

The shaft was actually worn very little.

So we bored the housing out and installed bronze bushings a cleaned the shaft.