Kent

One way to remove the yaw from a truck is to put a compression spring under the head of the screw holding one truck.   Use a very light spring.  Kadee is your best source for very light compression springs, making a wide variety for their many couplers, but I am not sure which ones I have used.  Possibly the O-scale knuckle spring.  It needs to be a loose fit over the screw, but these springs can be expanded by pushing onto a tapered mandrel.  I cut them in half, and bend the cut end in enough that it holds tight on the screw when the truck is removed.  Tighten the screw just enough to eliminate car body wobble.

John Stutz