David Maynard said:
Yea, when my Heartland 0-4-4 did that (climbed the frog) I found that the drivers on that locomotive were under gauge, and the trailing truck was over gauge. Checking and properly setting the gauge on my rolling stock has solved a lot of problems.
Checking should apply to every piece of rolling stock regardless of scale. Even the product from a very well respected HOm manufacturer had “amazing” variations in wheel gauge. For that scale/gauge I machined a number of sets of setting gauges which are very easy to use. Basic additional equipment required: a small bench vise. Correct gauge and no wobble.
PS many clubs won’t let rolling stock onto the layout unless it passes their QC.