Chevrolet Repair: power steering gearbox, alignment shop, king pins

Question
I have  a 1955 chevy have had for 3 months,and was fine until the other day I made a left turn and the steering seemed to lockup when it should have returned I gave a firm yank on the wheel and it came out of the turn but made a klunk when I pulled over and had my son turn the wheel left and right you can see the gearbox jerk a little and stick but not all the time and only on the way back to center. The gearbox looks to be new any help would be great  THANKS
                                      Mike

Answer
There is an adjustment in it to eliminate slack, and it should have just a tiny bit of drag right at center, when the wheels are off the ground, or disconnected.
Yours may be too tight.
Could also be something in one of the wheel suspensions catching, which may explain why it has a new gearbox, which may not have cured the problem for the former owner.
That problem might not show up with the wheels off the ground. Some roller pads for the tires to sit on, like at an alignment shop would help in finding that.
That have king pins and bushings, or ball joints?

Van