I took the tailwheel apart again this week to study it more closely. I compared the JD Air Parts control arm to the original Vans arm I had used when I was using chains and springs. The tailwheel steering had worked perfectly with the original Vans arm, but I changed to the JD Air Parts Tail Link as the chains were hitting the bottom of the rudder. I had put some clear flexible hose over the chains to protect the rudder, but it seemed like it was just a matter of time before the paint got banged up.

I noted that the slot for the lock/unlock plunger was not quite as long on the JD Air Parts arm as it was on the Vans arm. Also, I noted that the sides of the slot on the JD Air Parts arm were not quite parallel - the slot was wider at the open end than it was at the closed end. Also, the corners of end of the plunger had a bit larger radius than optinum. The combination of these three things meant the plunger tended to retract when pushing left rudder.

The replacement plunger that I purchased from Flyboy Accessories arrived this week. It had smaller radii on the corners than my plunger, so I switched to the new one. I did a bunch of taxiing around and a short test flight, and the tailwheel worked perfectly.

Update - I reported the issues with the control arm to JD Air Parts. I just got a reply saying that they were aware of the problems, and that they expected to receive new, improved parts from their contract manufacturer this week. They will send me a new one to try out.