Another really elegant solution, Peter. I must try something similar on a couple of wagons which have a longer wheelbase and sometimes struggle over my rather poorly laid trackwork.
I have used a similar approach to solve a problem I had with my double ended (ford-ish) railmotor bashed from a couple of early Andel coaches.
I seldom used them for around a couple of years after I had constructed them because they were so unreliable. They would leave the track at regular intervals. I tried replacing the wheels several times and adjusted the back to backs on numerous occasions without success. Eventually, after lying on my stomach and carefully scrutinising her negotiating a notorious black spot, I figured her long wheelbase and fixed chassis was the problem.
Fortunately, the wheels were attached to the body with GRS brass U-brackets.
It was a fairly simple process to solder a short length of brass rod along the centre line of one bracket on each coach and drill a hole at either end of the rod.
The brackets were then re-attached to the body with a couple of self-tappers, not fully tightened, so the brackets could wiggle.
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She is now one of my most reliable runners and I'll often get her out to run a quick passenger service when the fancy takes me.
Rik