Solved the original problem which started me on this thread. Brakes need constant checking. Last year I replaced the hub assembles making the balancing easier as everything is new except the drums themselves. To start with the adjustment is quite difficult until the new shoes are bedded in. I also found this weekend that the thread on the star adjusters were the reverse of the old ones and the ones described in the owners manual! I also took off the drums and cleaned them out with a mild detergent to make sure everything was clean and dust/grease free.
To get the balance, I spin each of the four wheels as fast as I can. I find that there is a maximum that I can achieve each time. I then get my partner to push the lever on the controller to a minimum voltage (1.7V on my Prodigy) so the brake doesn't just slam on but stops quickly with a quick scrape sound of about one second. I also check at different voltages so I feel sure they are giving me a similar response. I raise two opposite wheels at a time. I also find tyre pressures must also be exactly the same. Then after driving for half an hour or so with plenty of brake action, I put my hand behind the tyre to feel the side of the drums for variations in temperature.
Somebody once told me an infrared thermometer was a good way to check and read the temperatures for final adjustments. I'm happy if all drums feel warm and I don't have one too hot to touch or too cold to show signs of braking.