If the nut was too far on the threads then the washer wasn't thick enough. I went through this in 1996 with a '67 Barracuda that I bought. The car was overall in decent condition, but had a sloppy idler. There are no washer. Put a thick washer on and had no more problems with a sloppy idler
The problem with the old one was the ball joints were sloppy. I had to use a joint remover to pop the frame side and link side out. The tapered shaft on the new ball joints had a threaded section that was longer than it needed to be.
