There must be a technique to attaching the pitman arm to the knuckle (ball) on the sickle mower. I would imagine some technique to compress the spring, but haven't any luck yet. Lonnie
The picture up above is an "x-ray" view of the end of the pitman. It shows the coil spring pushing against the fork that keeps the "ball socket" closed. This automatically takes up the wear on the "ball" portion of the connection to the knife bar. The "secret" is part number 3, shown in the exploded drawing on the left. THAT part is called the "spring release", and if it is MISSING, you will have a hard time installing or removing the pitman.
The spring release is only held on by ONE bolt, and it sometimes gets LOST. (Remind me to check and see if this part is still available from the John Deere dealer). To attach the pitman, hold it down with your foot and insert a punch or a drift pin into the hole in the top of the spring release. Pry against the spring. This will release the tension on the two halves of the socket, and at the same time will force the wedge-shaped end between the two halves, spreading them apart. The pressure of your foot should snap the two halves over the ball.
To remove the pitman, insert a punch or pin through the hole in the spring and into the the yoke plunger. Force the yoke plunger back, and the end of the spring down between the straps (the two halves of the socket) to spread them. This will release them from the ball on the end of the knife bar.